https://rflab.martinos.org/api.php?action=feedcontributions&user=Dstraney&feedformat=atomRF Coil Lab - User contributions [en]2024-03-28T14:51:37ZUser contributionsMediaWiki 1.35.1https://rflab.martinos.org/index.php?title=File:Heart_Stimulator_documentation.zip&diff=734File:Heart Stimulator documentation.zip2022-05-26T20:46:52Z<p>Dstraney: Full docs for heart stimulator: Operating/maintenance procedures, technical description, drawings, BOM, etc.</p>
<hr />
<div>== Summary ==<br />
Full docs for heart stimulator: Operating/maintenance procedures, technical description, drawings, BOM, etc.</div>Dstraneyhttps://rflab.martinos.org/index.php?title=PIN_Diode_Driver_(8-channel)&diff=591PIN Diode Driver (8-channel)2021-05-12T11:11:14Z<p>Dstraney: sense input current</p>
<hr />
<div>== Overview ==<br />
[[File:PIN_diode_driver_8x.JPG|1200px]]<br /><br />
This PIN diode driver is intended to allow new RF coil designs to use more PIN diode channels than the Siemens scanners provide, especially for high-channel-count coil designs. Mounted to an RF coil, it takes on/off input control from an existing PIN diode line from the scanner, and drives the 8 channels in sync with the scanner's PIN diode line.<br />
<br />
Work contributed by Don Straney, Staff Electrical Engineer for the Martinos Center<br />
<br />
== Using the drivers ==<br />
=== Connections and Power ===<br />
Power inputs are +5V @ 1A (for forward bias), and -15V @ 10 mA (for reverse-bias). Each output provides 100 mA (nominal) when on, and approx. -14.5V when off.<br />
* Protection consists of two SMT fuses, one for +5V and one for -15V, and "resettable" PTC fuses in the reverse-bias drivers.<br />
* The +5V fuse is a Schurter [https://www.digikey.com/product-detail/en/schurter-inc/3413-0219-22/486-1147-1-ND/1522979 3413.0219.22], but any 1206-size 2A fast-blow fuse will work. The -15V fuse is a Schurter [https://www.digikey.com/product-detail/en/schurter-inc/3413-0213-22/486-1141-1-ND/1522973 3413.0213.22], but any 1206-size 0.2A to 0.5A fast-blow fuse will work.<br />
* A red LED (one for each fuse) will light if power is applied and one of the power input fuses is blown. This can happen due to reversed power supply polarity/incorrect power supply connection, power supply over-voltage, or shorted outputs. The fuses can be de-soldered and new ones soldered in place; it is not worth the extra size/space, risk of eddy currents or image artifacts, etc. to use replaceable fuses as there are few opportunities to blow the fuses through user error once the PIN drivers are incorporated into a permanent setup.<br />
* Do not replace the fuses with solid jumpers! This would likely cause parts to overheat and catch on fire in case of a fault, instead of a safe blown fuse to replace.<br />
Power connections are through a 2x2 Molex Mini-Fit Jr. connector. The pinout for this connector is shown on the top-side PCB silkscreen text next to the connector pins.<br />
Input sense connections and PIN driver output connections are through soldered through-hole connections.<br />
: There are two options for connecting the sense input to a scanner PIN diode line:<br />
# In series with an existing PIN diode: populate D1 and R1, and make sure D2 is removed<br />
[[File:PIN_diode_driver_8x-conn-input-series.png]]<br />
# As a stand-alone load on the scanner's line: populate D2, and make sure D1 and R1 are removed<br />
[[File:PIN_diode_driver_8x-conn-input-direct.png]]<br />
: The sense input is turned on by ~110 mA, to match the typical Siemens bias line current. It's electrically isolated from the rest of the circuitry and so there should be no sense connection concerns with ground loops, etc.<br />
Outputs can be combined into a single 800 mA output, by populating the 16 jumpers (0603-size) along the bottom edge of the PCB, and using the larger output through-hole connections near the bottom-left edge.<br />
<br />
=== Mechanical form factor ===<br />
See the mechanical drawing here for PCB dimensions, locations of mounting holes, and clearance needed above/below the PCB:<br />
[[Media:PIN_driver_8x-mech.pdf]]<br /><br />
The default mounting (as shown in the layout and on the silkscreen) for the Molex Mini-Fit Jr. power connector is on the bottom side of the board. However, if necessary for space constraints, this connector can also be installed on the top side of the board, or it can be left off completely (with wires soldered directly to the through-hole pads).<br />
<br />
The PIN driver can operate continuously with all channels on, at full current, without being damaged; however it does generate a reasonable amount of heat, so don't put it inside a closed box. Mounting an insulating sheet of plastic/fiberglass/etc. 10 mm above the top of the PCB is reasonable though, to keep conductive objects and dust from falling on it.<br />
<br />
=== Operation and Modifications ===<br />
'''Output current''' is not regulated, due to the difficulty of heatsinking transistors in-bore. The output current is set by driving the input +5V supply across a known resistance, into a known range of output voltages. The output current is designed to be 100 mA nominal, but will vary from 82 mA (for a 1.2V PIN diode voltage, in series with 10Ω total RF choke resistance) to 127 mA (for a 0.7V PIN diode voltage, no additional series resistance).<br />
* If the output current is higher than desired, the +5V supply can be lowered slightly. The nominal output resistance is 30Ω, so each 0.1V reduction in supply voltage will reduce output current on each channel by ~3.3 mA. Do not reduce supply voltage below 3.3V (limited by FODM8071). Reducing the +5V supply will also make the output current vary more if output voltage changes.<br />
* If the output current is lower than desired, the +5V supply can be increased slightly. Do not increase it beyond +5.4V (limited by FODM8071 optoisolator and logic inverter). Every 0.1V increase in supply voltage will increase output current on each channel by ~3.3 mA.<br />
* Output current can be increased or decreased further by increasing or decreasing the power resistor values on each channel (R24, R26, and R27 on channel 1, etc.). Do not make significant increases to the output current (>120 mA) lightly though! Many parts of the design are based around a 100 mA output current; any changes would need to account for output transistor power dissipation (MMBT2907), output transistor base current and min. beta, output resistor power dissipation and measured steady-state temperature with all channels continuously driving full current.<br />
The '''reverse-bias voltage''' has some room for adjustment:<br />
* If a lower reverse bias is desired (down to approx. -6V is possible), reduce R10's value so that it conducts about 3.5 mA or a little more.<br />
* If a higher reverse bias is desired, change or remove the 15V TVS diode D6. The largest limitation on the reverse-bias voltage is the 30V rating of the BAT54H Schottky diodes: in operation they see about 15V+5V=20V. I wouldn't recommend using any more than -20V reverse-bias. If the BAT54H parts are replaced with a similar small-signal Schottky diode with a higher voltage rating, the driver could tolerate up to -30V reverse-bias (limited by the MMBT2222 output transistors).<br />
'''Part substitutions''' are possible if some of the specific part numbers used in this design become unavailable. See "0 parts substitution notes.txt" in the design files.<br />
<br />There are inductors in series with each input power lines to serve as '''RF blocks'''; a high-impedance parallel resonant configuration was not possible due to the unexpectedly large/unpredictable parasitic capacitances. However, these still do provide some impedance at 100-300 Mhz.<br />
<br />'''Switching speed''' is slow, with up to 10µs turn-off time depending on configuration (8µs measured with a single large Macom PIN diode typically used for transmit switching in the RF Lab's coils). Because the Siemens scanner allows ~100µs for the switching to happen, this design is optimized for fairly low parts count, low off-state power, and robust design rather than switching speed.<br />
<br />
== Design files ==<br />
Design files were created in KiCAD 5<br /><br />
[[Media:PIN_driver_8x_1.1.1.zip]]<br /><br />
[[Media:PIN_driver_8x_1.2.zip]] Contains assembly files for automated assembly, through PCB Universe or another service</div>Dstraneyhttps://rflab.martinos.org/index.php?title=Current_driver:RevD&diff=588Current driver:RevD2021-05-11T19:09:32Z<p>Dstraney: </p>
<hr />
<div>== Introduction ==<br />
Revision D of the design is a major change from revision C, with real-time waveform playback, improved control loop performance, and easier assembly.<br />
<br />
== Design ==<br />
Similar to revision C, the user's computer communicates with the current driver box: a single digital control board which interfaces with multiple (up to 8) 8-channel amplifiers, each containing a DAC for setting output current, an ADC for monitoring output current, and 8 copies of the analog control loop and power amplifier. Each amplifier consists of two sections: a power board mounted to a heatsink, and a control board mounted to the power board. Power outputs run over ribbon cables to an ODU-MAC White-Line connector for connecting the shim coils.<br />
(Block diagram)<br />
<br />
'''Design files:'''<br /><br />
Amp control board: [[File:Amp_ctrl_revD1A.zip]]<br /><br />
Amp power board: [[File:Amp_pwr_revD1.zip]]<br /><br />
Digital control board: (TBD)<br /><br />
Output connector board: (TBD)<br /><br />
<br /><br />
Control loop compensation is adjustable for different shim coils by inserting through-hole components into connectors on the amp control board. The Octave/MATLAB script below will recommend component values to use based on your coil parameters and predict the control loop response.<br /><br />
[[File:Current_driver_compensation.zip]]<br />
<br />
== Assembly Instructions ==<br />
(TBD)<br />
<br />
== Performance ==<br />
=== Bandwidth / Step Response ===<br />
(TBD on final hardware)<br />
<br />
=== Gradient Rejection ===<br />
Gradient rejection ability was tested with the default 10 cm diameter single-loop shim coil by applying an external magnetic field from a loosely-coupled coil, and measuring the resulting shim coil current.<br />
Pink (channel 4) in the screenshots below is the voltage applied to the coupling coil, while green (channel 2) is the current in the shim coil.<br />
<br />
'''Without shim amplifier: open leads, induced voltage''' (yellow, channel 1)<br /><br />
[[File:Gradient_rejection_-_uncorrected_open.png|500px]]<br />
<br /><br /><br />
'''Without shim amplifier: shorted leads, induced current'''<br /><br />
[[File:Gradient_rejection_-_uncorrected_short.png|500px]]<br />
<br /><br /><br />
'''Revision C amplifier:'''<br /><br />
[[File:Gradient_rejection_-_revC.png|500px]]<br />
<br /><br /><br />
'''Revision D amplifier:'''<br /><br />
[[File:Gradient_rejection_-_revD.png|500px]]<br />
<br /><br /><br />
For the test setup, an AE Techron 7224 was used in constant-voltage mode to drive the coupling coil, which consisted of 18 turns of 20 AWG magnet wire wrapped solenoid-style on a TDK-Epcos B64290A0084X038 ferrite core (measured 102 µH @ 100 kHz), intended to increase the inductance of the coupling coil and make higher voltages easier to drive without excessive magnetizing current. The coupling coil was mounted co-axial with the shim coil, strapped to the opposite side of a piece of 1.6 mm FR-4.<br /><br />
[[File:Gradient_rejection_setup.jpg|800px]]<br /><br />
The ferrite core only changed the shim coil's original inductance by +2.3% (2.64 µH -> 2.70 µH without extension leads), and the estimated coupling coefficient from the shim coil to coupling coil was only 1.1% (shim coil inductance dropped from 2.70 µH to 2.67 µH when coupling coil leads were shorted). The original circuit parameters and compensation were therefore not noticeably affected. The extension leads, which increase overall shim coil inductance to 7.9 µH + 1.5Ω @ 100 kHz, were used during the test, as with every test involving this default shim coil, to accurately represent the shim cabling used in the scanner.</div>Dstraneyhttps://rflab.martinos.org/index.php?title=Current_driver:RevD&diff=585Current driver:RevD2021-05-11T19:07:09Z<p>Dstraney: </p>
<hr />
<div>== Introduction ==<br />
Revision D of the design is a major change from revision C, with real-time waveform playback, improved control loop performance, and easier assembly.<br />
<br />
== Design ==<br />
Similar to revision C, the user's computer communicates with the current driver box: a single digital control board which interfaces with multiple (up to 8) 8-channel amplifiers, each containing a DAC for setting output current, an ADC for monitoring output current, and 8 copies of the analog control loop and power amplifier. Each amplifier consists of two sections: a power board mounted to a heatsink, and a control board mounted to the power board. Power outputs run over ribbon cables to an ODU-MAC White-Line connector for connecting the shim coils.<br />
(Block diagram)<br />
<br />
'''Design files:'''<br /><br />
Amp control board: [[File:Amp_ctrl_revD1A.zip]]<br /><br />
Amp power board: [[File:Amp_pwr_revD1.zip]]<br /><br />
Digital control board: (TBD)<br /><br />
Output connector board: (TBD)<br /><br />
<br /><br />
Control loop compensation is adjustable for different shim coils by inserting through-hole components into connectors on the amp control board. The Octave/MATLAB script below will recommend component values to use based on your coil parameters and predict the control loop response.<br /><br />
[[File:Current_driver_compensation.zip]]<br />
<br />
== Assembly Instructions ==<br />
(TBD)<br />
<br />
== Performance ==<br />
=== Bandwidth / Step Response ===<br />
(TBD on final hardware)<br />
<br />
=== Gradient Rejection ===<br />
Gradient rejection ability was tested with the default 10 cm diameter single-loop shim coil by applying an external magnetic field from a loosely-coupled coil, and measuring the resulting shim coil current.<br />
Pink (channel 4) in the screenshots below is the voltage applied to the coupling coil, while green (channel 2) is the current in the shim coil.<br />
<br />
'''Without shim amplifier: induced voltage''' (yellow, channel 1)<br /><br />
[[File:Gradient_rejection_-_uncorrected_open.png|500px]]<br />
<br /><br /><br />
'''Without shim amplifier: shorted leads'''<br /><br />
[[File:Gradient_rejection_-_uncorrected_short.png|500px]]<br />
<br /><br /><br />
'''Revision C amplifier:'''<br /><br />
[[File:Gradient_rejection_-_revC.png|500px]]<br />
<br /><br /><br />
'''Revision D amplifier:'''<br /><br />
[[File:Gradient_rejection_-_revD.png|500px]]<br />
<br /><br /><br />
For the test setup, an AE Techron 7224 was used in constant-voltage mode to drive the coupling coil, which consisted of 18 turns of 20 AWG magnet wire wrapped solenoid-style on a TDK-Epcos B64290A0084X038 ferrite core (measured 102 µH @ 100 kHz), intended to increase the inductance of the coupling coil and make higher voltages easier to drive without excessive magnetizing current. The coupling coil was mounted co-axial with the shim coil, strapped to the opposite side of a piece of 1.6 mm FR-4.<br /><br />
[[File:Gradient_rejection_setup.jpg|800px]]<br /><br />
The ferrite core only changed the shim coil's original inductance by +2.3% (2.64 µH -> 2.70 µH without extension leads), and the estimated coupling coefficient from the shim coil to coupling coil was only 1.1% (shim coil inductance dropped from 2.70 µH to 2.67 µH when coupling coil leads were shorted). The original circuit parameters and compensation were therefore not noticeably affected. The extension leads, which increase overall shim coil inductance to 7.9 µH + 1.5Ω @ 100 kHz, were used during the test, as with every test involving this default shim coil, to accurately represent the shim cabling used in the scanner.</div>Dstraneyhttps://rflab.martinos.org/index.php?title=Current_driver:Current_driver&diff=582Current driver:Current driver2021-05-11T19:02:57Z<p>Dstraney: Added rev. D link</p>
<hr />
<div><br />
'''''*UPDATE*''' A limited number of populated Revision C 8ch amplifier boards are now available on an open source basis. Please contact us if you would like us to send you amplifier boards for your research projects. <br />
''<br />
<br />
In collaboration with Jacob White, Nicolas Arango, and Irene Kuang at MIT, we have developed a low-cost 8-channel digitally-programmable current driver that can supply up to 8 amps DC per channel (up to 60 volt output). The circuit board design and control software were created by Nicolas Arango and Irene Kuang. <br />
<br />
The board is intended as a scalable solution for supplying current to matrix shim coil arrays that require an independent, dynamically-switchable current driver for each shim coil element. Cost per channel is ~$100. The circuit uses a simple feedback control topology built around OPA549 linear power stage op amps in a push-pull configuration. The voltage across a current sense resistor is sensed in the feedback topology to allow control of the actual current output to the load. The resistors and capacitors in the feedback loops can be adjusted to ensure stability for driving a particular load impedance. With the component values used in the board files (see below), the feedback loop compensation elements is set up to compensate a 10 uH reactive load. The design retains sufficient gain in the audio frequency range to reject disturbances caused by gradient coil switching in the MRI scanner environment. The end result is a stable output current (>45 deg phase margin) with ~50us rise time and very good disturbance rejection for maintaining stable shim currents during MR acquisitions. The outputs of each channel can be tied together to increase the current beyond 8 amps. For most loads, heat sinking the OPA549s is required since most of the voltage drop (and heat dissipation) will occur inside these ICs. <br />
<br />
The board, as configured will work up to 25V. For higher voltage operation (up to 60V) higher voltage capacitors must be used and some digital circuitry must be removed. A version with "no-stuff" declarations for 60V operation is in progress.<br />
<br />
An 8-channel 16-bit DAC is used to update the current setting on each channel. The current sense resistor voltage drop is buffered and sent to an ADC so that the output current on each channel can be monitored by computer. Presently the board is controlled using a Teensy Arduino 3.5 microcontroller. We have created (and shared) a Teensy daughterboard that includes fiber optic transmitters and receivers for communicating with the amplifiers via a fiber optic interface board.<br />
<br />
<br />
''Update (May 2021): Revision D is in progress - see preliminary design files and test data at [[Current driver:RevD]].''<br />
<br />
''Update (July, 2018): Revision C of the board files is now available! See below for details.<br />
<br />
<br />
Please contact us for more details:<br />
<br />
Jason Stockmann: [mailto:jstockmann@mgh.harvard.edu jstockmann@mgh.harvard.edu]''<br />
<br />
<br />
<br />
'''[https://rflab.martinos.org/images/6/68/COPIES_for_UPLOAD_TO_WIKI_APRIL_2020.zip Click here] to download Eagle files and GERBER files for Revision C, Version 6 of the amplifier set up. This release fixes several bugs on the fiber optic interface board: (1) Diode polarity on power supply line was flipped, (2) Pin 1 on the 74HCT244 buffer was not grounded, and (3) The 74LS151 buffers have been updated to 74HCT151.''' The download package includes: (a) 8ch amplifier boards, (b) fiber optic interface board, (c) Arduino Teensy daughter board for interfacing with a PC. Control software is also included for using an Arduino Teensy 3.5 to control the shim amplifiers from a PC.<br />
<br />
''[https://rflab.martinos.org/images/5/57/Setup_guidelines_shim_board_revC_V7.pptx Click here] to download slides describing how to assemble the needed components for using the shim amplifier boards, and other practical details. The Powerpoint slides also discuss how to use the Teensy microcontroller serial controller interface.<br />
''<br />
<br />
In addition to the Quick Start guide, please read the [[startup notes]] which include pointers on setting up the Teensy control software. <br />
<br />
======================================================<br />
'''NOTES ON OLD BOARD RELEASES<br />
'''<br />
<br />
'''Obsolete board release from July 2018 is available for download here (Rev. C, Version 4): [https://rflab.martinos.org/images/4/42/July_28_2018_board_files.zip Click here]<br />
<br />
'''Info related to Rev. A of the board (now obsolete):<br />
'''<br />
[https://rflab.martinos.org/images/0/01/Shimboard_revA_V4.zip Click here] to download Eagle board file and schematic as well as GERBER files for board fabrication. A Matlab script is also included in the download for modeling the step response and transfer function of the analog stage (Bode plot). This software can be used to figure out the correct compensation circuit values to use for a particular load. Typically the compensation is adjusted by changing two capacitors in the feedback loop. <br />
<br />
<br />
<br />
<br />
<br />
[[File:Picture1.png|left|800px|thumbnail|alt=Alt|Schematic for current feedback control loop topology showing 0.2 ohm current sense resistor and OPA549 power op amps in push-pull configuration]]<br />
<br />
<br />
<br />
[[File:shim supply 8ch photo.png|left|800px |alt=Alt|thumbnail|8ch current driver board with key components highlighted.]]<br />
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<br /></div>Dstraneyhttps://rflab.martinos.org/index.php?title=Current_driver:RevD&diff=579Current driver:RevD2021-05-11T18:59:27Z<p>Dstraney: </p>
<hr />
<div>== Introduction ==<br />
Revision D of the design is a major change from revision C, with real-time waveform playback, improved control loop performance, and easier assembly.<br />
<br />
== Design ==<br />
Similar to revision C, the user's computer communicates with the current driver box: a single digital control board which interfaces with multiple (up to 8) 8-channel amplifiers, each containing a DAC for setting output current, an ADC for monitoring output current, and 8 copies of the analog control loop and power amplifier. Each amplifier consists of two sections: a power board mounted to a heatsink, and a control board mounted to the power board. Power outputs run over ribbon cables to an ODU-MAC White-Line connector for connecting the shim coils.<br />
(Block diagram)<br />
<br />
Design files:<br />
Amp control board: [[File:Amp_ctrl_revD1A.zip]]<br />
Amp power board: [[File:Amp_pwr_revD1.zip]]<br />
Digital control board: (TBD)<br />
Output connector board: (TBD)<br />
<br />
Control loop compensation is adjustable for different shim coils by inserting through-hole components into connectors on the amp control board. The Octave/MATLAB script below will recommend component values to use based on your coil parameters and predict the control loop response.<br />
[[File:Current_driver_compensation.zip]]<br />
<br />
== Assembly Instructions ==<br />
(TBD)<br />
<br />
== Performance ==<br />
=== Bandwidth / Step Response ===<br />
(TBD on final hardware)<br />
<br />
=== Gradient Rejection ===<br />
Gradient rejection ability was tested with the default 10 cm diameter single-loop shim coil by applying an external magnetic field from a loosely-coupled coil, and measuring the resulting shim coil current.<br />
Pink (channel 4) in the screenshots below is the voltage applied to the coupling coil, while green (channel 2) is the current in the shim coil.<br />
<br />
'''Without shim amplifier: induced voltage''' (yellow, channel 1)<br /><br />
[[File:Gradient_rejection_-_uncorrected_open.png|500px]]<br />
<br /><br /><br />
'''Without shim amplifier: shorted leads'''<br /><br />
[[File:Gradient_rejection_-_uncorrected_short.png|500px]]<br />
<br /><br /><br />
'''Revision C amplifier:'''<br /><br />
[[File:Gradient_rejection_-_revC.png|500px]]<br />
<br /><br /><br />
'''Revision D amplifier:'''<br /><br />
[[File:Gradient_rejection_-_revD.png|500px]]<br />
<br /><br /><br />
For the test setup, an AE Techron 7224 was used in constant-voltage mode to drive the coupling coil, which consisted of 18 turns of 20 AWG magnet wire wrapped solenoid-style on a TDK-Epcos B64290A0084X038 ferrite core (measured 102 µH @ 100 kHz), intended to increase the inductance of the coupling coil and make higher voltages easier to drive without excessive magnetizing current. The coupling coil was mounted co-axial with the shim coil, strapped to the opposite side of a piece of 1.6 mm FR-4.<br /><br />
[[File:Gradient_rejection_setup.jpg|800px]]<br /><br />
The ferrite core only changed the shim coil's original inductance by +2.3% (2.64 µH -> 2.70 µH without extension leads), and the estimated coupling coefficient from the shim coil to coupling coil was only 1.1% (shim coil inductance dropped from 2.70 µH to 2.67 µH when coupling coil leads were shorted). The original circuit parameters and compensation were therefore not noticeably affected. The extension leads, which increase overall shim coil inductance to 7.9 µH + 1.5Ω @ 100 kHz, were used during the test, as with every test involving this default shim coil, to accurately represent the shim cabling used in the scanner.</div>Dstraneyhttps://rflab.martinos.org/index.php?title=Current_driver:RevD&diff=576Current driver:RevD2021-05-11T18:58:28Z<p>Dstraney: images</p>
<hr />
<div>== Introduction ==<br />
Revision D of the design is a major change from revision C, with real-time waveform playback, improved control loop performance, and easier assembly.<br />
<br />
== Design ==<br />
Similar to revision C, the user's computer communicates with the current driver box: a single digital control board which interfaces with multiple (up to 8) 8-channel amplifiers, each containing a DAC for setting output current, an ADC for monitoring output current, and 8 copies of the analog control loop and power amplifier. Each amplifier consists of two sections: a power board mounted to a heatsink, and a control board mounted to the power board. Power outputs run over ribbon cables to an ODU-MAC White-Line connector for connecting the shim coils.<br />
(Block diagram)<br />
<br />
Design files:<br />
Amp control board: [[File:Amp_ctrl_revD1A.zip]]<br />
Amp power board: [[File:Amp_pwr_revD1.zip]]<br />
Digital control board: (TBD)<br />
Output connector board: (TBD)<br />
<br />
Control loop compensation is adjustable for different shim coils by inserting through-hole components into connectors on the amp control board. The Octave/MATLAB script below will recommend component values to use based on your coil parameters and predict the control loop response.<br />
[[File:Current_driver_compensation.zip]]<br />
<br />
== Assembly Instructions ==<br />
(TBD)<br />
<br />
== Performance ==<br />
=== Bandwidth / Step Response ===<br />
(TBD on final hardware)<br />
<br />
=== Gradient Rejection ===<br />
Gradient rejection ability was tested with the default 10 cm diameter single-loop shim coil by applying an external magnetic field from a loosely-coupled coil and measuring the coil current.<br />
Pink (channel 4) in the screenshots below is the voltage applied to the coupling coil, while green (channel 2) is the current in the shim coil.<br />
<br />
'''Without shim amplifier: induced voltage''' (yellow, channel 1)<br /><br />
[[File:Gradient_rejection_-_uncorrected_open.png|500px]]<br />
<br /><br /><br />
'''Without shim amplifier: shorted leads'''<br /><br />
[[File:Gradient_rejection_-_uncorrected_short.png|500px]]<br />
<br /><br /><br />
'''Revision C amplifier:'''<br /><br />
[[File:Gradient_rejection_-_revC.png|500px]]<br />
<br /><br /><br />
'''Revision D amplifier:'''<br /><br />
[[File:Gradient_rejection_-_revD.png|500px]]<br />
<br /><br /><br />
For the test setup, an AE Techron 7224 was used in constant-voltage mode to drive the coupling coil, which consisted of 18 turns of 20 AWG magnet wire wrapped solenoid-style on a TDK-Epcos B64290A0084X038 ferrite core (measured 102 µH @ 100 kHz), intended to increase the inductance of the coupling coil and make higher voltages easier to drive without excessive magnetizing current. The coupling coil was mounted co-axial with the shim coil, strapped to the opposite side of a piece of 1.6 mm FR-4.<br /><br />
[[File:Gradient_rejection_setup.jpg|800px]]<br /><br />
The ferrite core only changed the shim coil's original inductance by +2.3% (2.64 µH -> 2.70 µH without extension leads), and the estimated coupling coefficient from the shim coil to coupling coil was only 1.1% (shim coil inductance dropped from 2.70 µH to 2.67 µH when coupling coil leads were shorted). The original circuit parameters and compensation were therefore not noticeably affected. The extension leads, which increase overall shim coil inductance to 7.9 µH + 1.5Ω @ 100 kHz, were used during the test, as with every test involving this default shim coil, to accurately represent the shim cabling used in the scanner.</div>Dstraneyhttps://rflab.martinos.org/index.php?title=Current_driver:RevD&diff=573Current driver:RevD2021-05-11T18:51:00Z<p>Dstraney: </p>
<hr />
<div>== Introduction ==<br />
Revision D of the design is a major change from revision C, with real-time waveform playback, improved control loop performance, and easier assembly.<br />
<br />
== Design ==<br />
Similar to revision C, the user's computer communicates with the current driver box: a single digital control board which interfaces with multiple (up to 8) 8-channel amplifiers, each containing a DAC for setting output current, an ADC for monitoring output current, and 8 copies of the analog control loop and power amplifier. Each amplifier consists of two sections: a power board mounted to a heatsink, and a control board mounted to the power board. Power outputs run over ribbon cables to an ODU-MAC White-Line connector for connecting the shim coils.<br />
(Block diagram)<br />
<br />
Design files:<br />
Amp control board: [[File:Amp_ctrl_revD1A.zip]]<br />
Amp power board: [[File:Amp_pwr_revD1.zip]]<br />
Digital control board: (TBD)<br />
Output connector board: (TBD)<br />
<br />
Control loop compensation is adjustable for different shim coils by inserting through-hole components into connectors on the amp control board. The Octave/MATLAB script below will recommend component values to use based on your coil parameters and predict the control loop response.<br />
[[File:Current_driver_compensation.zip]]<br />
<br />
== Assembly Instructions ==<br />
(TBD)<br />
<br />
== Performance ==<br />
=== Bandwidth / Step Response ===<br />
(TBD on final hardware)<br />
<br />
=== Gradient Rejection ===<br />
Gradient rejection ability was tested with the default 10 cm diameter single-loop shim coil by applying an external magnetic field from a loosely-coupled coil and measuring the coil current.<br />
Pink (channel 4) in the screenshots below is the voltage applied to the coupling coil, while green (channel 2) is the current in the shim coil.<br />
<br />
Without shim amplifier: induced voltage (yellow, channel 1)<br />
[[File:Gradient_rejection_-_uncorrected_open.png]]<br />
<br />
Without shim amplifier: shorted leads<br />
[[File:Gradient_rejection_-_uncorrected_short.png]]<br />
<br />
Revision C amplifier:<br />
[[File:Gradient_rejection_-_revC.png]]<br />
<br />
Revision D amplifier:<br />
[[File:Gradient_rejection_-_revD.png]]<br />
<br />
For the test setup, an AE Techron 7224 was used in constant-voltage mode to drive the coupling coil, which consisted of 18 turns of 20 AWG magnet wire wrapped solenoid-style on a TDK-Epcos B64290A0084X038 ferrite core (measured 102 µH @ 100 kHz), intended to increase the inductance of the coupling coil and make higher voltages easier to drive without excessive magnetizing current. The coupling coil was mounted co-axial with the shim coil, strapped to the opposite side of a piece of 1.6 mm FR-4.<br />
[[File:Gradient_rejection_setup.jpg]]<br />
The ferrite core only changed the shim coil's original inductance by +2.3% (2.64 µH -> 2.70 µH without extension leads), and the estimated coupling coefficient from the shim coil to coupling coil was only 1.1% (shim coil inductance dropped from 2.70 µH to 2.67 µH when coupling coil leads were shorted). The extension leads, which increase overall shim coil inductance to 7.9 µH + 1.5Ω @ 100 kHz, were used during the test, as with every test involving this default shim coil, to accurately represent the shim cabling used in the scanner.</div>Dstraneyhttps://rflab.martinos.org/index.php?title=Current_driver:RevD&diff=570Current driver:RevD2021-05-11T18:49:05Z<p>Dstraney: performance</p>
<hr />
<div>== Introduction ==<br />
Revision D of the design is a major change from revision C, with real-time waveform playback, improved control loop performance, and easier assembly.<br />
<br />
== Design ==<br />
Similar to revision C, the user's computer communicates with the current driver box: a single digital control board which interfaces with multiple (up to 8) 8-channel amplifiers, each containing a DAC for setting output current, an ADC for monitoring output current, and 8 copies of the analog control loop and power amplifier. Each amplifier consists of two sections: a power board mounted to a heatsink, and a control board mounted to the power board. Power outputs run over ribbon cables to an ODU-MAC White-Line connector for connecting the shim coils.<br />
(Block diagram)<br />
<br />
Design files:<br />
Amp control board: [[File:Amp_ctrl_revD1A.zip]]<br />
Amp power board: [[File:Amp_pwr_revD1.zip]]<br />
Digital control board: (TBD)<br />
Output connector board: (TBD)<br />
<br />
Control loop compensation is adjustable for different shim coils by inserting through-hole components into connectors on the amp control board. The Octave/MATLAB script below will recommend component values to use based on your coil parameters and predict the control loop response.<br />
[[File:Current_driver_compensation.zip]]<br />
<br />
== Assembly Instructions ==<br />
(TBD)<br />
<br />
== Performance ==<br />
=== Bandwidth / Step Response ===<br />
(TBD on final hardware)<br />
<br />
=== Gradient Rejection ===<br />
Gradient rejection ability was tested with the default 10 cm diameter single-loop shim coil by applying an external magnetic field from a loosely-coupled coil and measuring the coil current.<br />
Pink (channel 4) in the screenshots below is the voltage applied to the coupling coil, while green (channel 2) is the current in the shim coil.<br />
<br />
Without shim amplifier: induced voltage (yellow, channel 1)<br />
[[File:Gradient_rejection_-_uncorrected_open.png|thumb]]<br />
<br />
Without shim amplifier: shorted leads<br />
[[File:Gradient_rejection_-_uncorrected_short.png|thumb]]<br />
<br />
Revision C amplifier:<br />
[[File:Gradient_rejection_-_revC.png|thumb]]<br />
<br />
Revision D amplifier:<br />
File:Gradient_rejection_-_revD.png|thumb]]<br />
<br />
For the test setup, an AE Techron 7224 was used in constant-voltage mode to drive the coupling coil, which consisted of 18 turns of 20 AWG magnet wire wrapped solenoid-style on a TDK-Epcos B64290A0084X038 ferrite core (measured 102 µH @ 100 kHz), intended to increase the inductance of the coupling coil and make higher voltages easier to drive without excessive magnetizing current. The coupling coil was mounted co-axial with the shim coil, strapped to the opposite side of a piece of 1.6 mm FR-4.<br />
[[File:Gradient_rejection_setup.jpg|thumb]]<br />
The ferrite core only changed the shim coil's original inductance by +2.3% (2.64 µH -> 2.70 µH without extension leads), and the estimated coupling coefficient from the shim coil to coupling coil was only 1.1% (shim coil inductance dropped from 2.70 µH to 2.67 µH when coupling coil leads were shorted). The extension leads, which increase overall shim coil inductance to 7.9 µH + 1.5Ω @ 100 kHz, were used during the test, as with every test involving this default shim coil, to accurately represent the shim cabling used in the scanner.</div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:Gradient_rejection_setup.jpg&diff=567File:Gradient rejection setup.jpg2021-05-11T18:42:33Z<p>Dstraney: </p>
<hr />
<div></div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:Gradient_rejection_-_revD.png&diff=564File:Gradient rejection - revD.png2021-05-11T18:36:44Z<p>Dstraney: </p>
<hr />
<div></div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:Gradient_rejection_-_revC.png&diff=561File:Gradient rejection - revC.png2021-05-11T18:36:32Z<p>Dstraney: </p>
<hr />
<div></div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:Gradient_rejection_-_uncorrected_short.png&diff=558File:Gradient rejection - uncorrected short.png2021-05-11T18:35:38Z<p>Dstraney: </p>
<hr />
<div></div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:Gradient_rejection_-_uncorrected_open.png&diff=555File:Gradient rejection - uncorrected open.png2021-05-11T18:32:46Z<p>Dstraney: </p>
<hr />
<div></div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:Current_driver_compensation.zip&diff=552File:Current driver compensation.zip2021-05-11T18:25:23Z<p>Dstraney: Compensation adjustment instructions and software for current drivers</p>
<hr />
<div>== Summary ==<br />
Compensation adjustment instructions and software for current drivers</div>Dstraneyhttps://rflab.martinos.org/index.php?title=Current_driver:RevD&diff=549Current driver:RevD2021-05-11T16:40:23Z<p>Dstraney: initial</p>
<hr />
<div>== Introduction ==<br />
Revision D of the design is a major change from revision C, with real-time waveform playback, improved control loop performance, and better [https://en.wikipedia.org/wiki/Design_for_manufacturability DFM].<br />
<br />
== Design ==<br />
Similar to revision C, the user's computer communicates with the current driver box: a single digital control board which interfaces with multiple (up to 8) 8-channel amplifier boards, each containing a DAC for setting output current, an ADC for monitoring output current, and 8 copies of the analog control loop and power amplifier. Each amplifier board consists of two sections: a power section mounted to a heatsink, and a control section mounted to the power section. Power outputs run over ribbon cables to an ODU-MAC White-Line connector for connecting the shim coils.<br />
(Block diagram)<br />
<br />
Design files:<br />
Amp control board: [[File:Amp_ctrl_revD1A.zip]]<br />
Amp power board: [[File:Amp_pwr_revD1.zip]]<br />
Digital control board: (TBD)<br />
Output connector board: (TBD)<br />
<br />
== Assembly Instruction ==<br />
(TBD)<br />
<br />
== Performance ==</div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:Amp_pwr_revD1.zip&diff=546File:Amp pwr revD1.zip2021-05-11T16:39:15Z<p>Dstraney: Current driver: revision D1 amp power board</p>
<hr />
<div>== Summary ==<br />
Current driver: revision D1 amp power board</div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:Amp_ctrl_revD1A.zip&diff=543File:Amp ctrl revD1A.zip2021-05-11T16:38:22Z<p>Dstraney: Current driver: revision D1A amp control board</p>
<hr />
<div>== Summary ==<br />
Current driver: revision D1A amp control board</div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:PIN_driver_8x_1.2.zip&diff=292File:PIN driver 8x 1.2.zip2020-07-01T17:08:07Z<p>Dstraney: Dstraney uploaded a new version of File:PIN driver 8x 1.2.zip</p>
<hr />
<div>PIN diode driver, 8-channel<br />
Version 1.2</div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:PIN_driver_8x_1.2.zip&diff=289File:PIN driver 8x 1.2.zip2020-07-01T15:26:50Z<p>Dstraney: PIN diode driver, 8-channel
Version 1.2</p>
<hr />
<div>PIN diode driver, 8-channel<br />
Version 1.2</div>Dstraneyhttps://rflab.martinos.org/index.php?title=PIN_Diode_Driver_(8-channel)&diff=286PIN Diode Driver (8-channel)2020-07-01T15:26:09Z<p>Dstraney: Added version 1.2 files, w/notes on automated assembly service</p>
<hr />
<div>== Overview ==<br />
[[File:PIN_diode_driver_8x.JPG]]<br /><br />
This PIN diode driver is intended to allow new RF coil designs to use more PIN diode channels than the Siemens scanners provide, especially for high-channel-count coil designs. Mounted to an RF coil, it takes on/off input control from an existing PIN diode line from the scanner, and drives the 8 channels in sync with the scanner's PIN diode line.<br />
<br />
== Using the drivers ==<br />
=== Connections and Power ===<br />
Power inputs are +5V @ 1A (for forward bias), and -15V @ 10 mA (for reverse-bias). Each output provides 100 mA (nominal) when on, and approx. -14.5V when off.<br />
* Protection consists of two SMT fuses, one for +5V and one for -15V, and "resettable" PTC fuses in the reverse-bias drivers.<br />
* The +5V fuse is a Schurter [https://www.digikey.com/product-detail/en/schurter-inc/3413-0219-22/486-1147-1-ND/1522979 3413.0219.22], but any 1206-size 2A fast-blow fuse will work. The -15V fuse is a Schurter [https://www.digikey.com/product-detail/en/schurter-inc/3413-0213-22/486-1141-1-ND/1522973 3413.0213.22], but any 1206-size 0.2A to 0.5A fast-blow fuse will work.<br />
* A red LED (one for each fuse) will light if power is applied and one of the power input fuses is blown. This can happen due to reversed power supply polarity/incorrect power supply connection, power supply over-voltage, or shorted outputs. The fuses can be de-soldered and new ones soldered in place; it is not worth the extra size/space, risk of eddy currents or image artifacts, etc. to use replaceable fuses as there are few opportunities to blow the fuses through user error once the PIN drivers are incorporated into a permanent setup.<br />
* Do not replace the fuses with solid jumpers! This would likely cause parts to overheat and catch on fire in case of a fault, instead of a safe blown fuse to replace.<br />
Power connections are through a 2x2 Molex Mini-Fit Jr. connector. The pinout for this connector is shown on the top-side PCB silkscreen text next to the connector pins.<br />
Input sense connections and PIN driver output connections are through soldered through-hole connections.<br />
: There are two options for connecting the sense input to a scanner PIN diode line:<br />
# In series with an existing PIN diode: populate D1 and R1, and make sure D2 is removed<br />
[[File:PIN_diode_driver_8x-conn-input-series.png]]<br />
# As a stand-alone load on the scanner's line: populate D2, and make sure D1 and R1 are removed<br />
[[File:PIN_diode_driver_8x-conn-input-direct.png]]<br />
: The sense input is electrically isolated from the rest of the circuitry and so there should be no sense connection concerns with ground loops, etc.<br />
Outputs can be combined into a single 800 mA output, by populating the 16 jumpers (0603-size) along the bottom edge of the PCB, and using the larger output through-hole connections near the bottom-left edge.<br />
<br />
=== Mechanical form factor ===<br />
See the mechanical drawing here for PCB dimensions, locations of mounting holes, and clearance needed above/below the PCB:<br />
[[Media:PIN_driver_8x-mech.pdf]]<br /><br />
The default mounting (as shown in the layout and on the silkscreen) for the Molex Mini-Fit Jr. power connector is on the bottom side of the board. However, if necessary for space constraints, this connector can also be installed on the top side of the board, or it can be left off completely (with wires soldered directly to the through-hole pads).<br />
<br />
The PIN driver can operate continuously with all channels on, at full current, without being damaged; however it does generate a reasonable amount of heat, so don't put it inside a closed box. Mounting an insulating sheet of plastic/fiberglass/etc. 10 mm above the top of the PCB is reasonable though, to keep conductive objects and dust from falling on it.<br />
<br />
=== Operation and Modifications ===<br />
'''Output current''' is not regulated, due to the difficulty of heatsinking transistors in-bore. The output current is set by driving the input +5V supply across a known resistance, into a known range of output voltages. The output current is designed to be 100 mA nominal, but will vary from 82 mA (for a 1.2V PIN diode voltage, in series with 10Ω total RF choke resistance) to 127 mA (for a 0.7V PIN diode voltage, no additional series resistance).<br />
* If the output current is higher than desired, the +5V supply can be lowered slightly. The nominal output resistance is 30Ω, so each 0.1V reduction in supply voltage will reduce output current on each channel by ~3.3 mA. Do not reduce supply voltage below 3.3V (limited by FODM8071). Reducing the +5V supply will also make the output current vary more if output voltage changes.<br />
* If the output current is lower than desired, the +5V supply can be increased slightly. Do not increase it beyond +5.4V (limited by FODM8071 optoisolator and logic inverter). Every 0.1V increase in supply voltage will increase output current on each channel by ~3.3 mA.<br />
* Output current can be increased or decreased further by increasing or decreasing the power resistor values on each channel (R24, R26, and R27 on channel 1, etc.). Do not make significant increases to the output current (>120 mA) lightly though! Many parts of the design are based around a 100 mA output current; any changes would need to account for output transistor power dissipation (MMBT2907), output transistor base current and min. beta, output resistor power dissipation and measured steady-state temperature with all channels continuously driving full current.<br />
The '''reverse-bias voltage''' has some room for adjustment:<br />
* If a lower reverse bias is desired (down to approx. -6V is possible), reduce R10's value so that it conducts about 3.5 mA or a little more.<br />
* If a higher reverse bias is desired, change or remove the 15V TVS diode D6. The largest limitation on the reverse-bias voltage is the 30V rating of the BAT54H Schottky diodes: in operation they see about 15V+5V=20V. I wouldn't recommend using any more than -20V reverse-bias. If the BAT54H parts are replaced with a similar small-signal Schottky diode with a higher voltage rating, the driver could tolerate up to -30V reverse-bias (limited by the MMBT2222 output transistors).<br />
'''Part substitutions''' are possible if some of the specific part numbers used in this design become unavailable. See "0 parts substitution notes.txt" in the design files.<br />
<br />There are inductors in series with each input power lines to serve as '''RF blocks'''; a high-impedance parallel resonant configuration was not possible due to the unexpectedly large/unpredictable parasitic capacitances. However, these still do provide some impedance at 100-300 Mhz.<br />
<br />'''Switching speed''' is slow, with up to 10µs turn-off time depending on configuration (8µs measured with a single large Macom PIN diode typically used for transmit switching in the RF Lab's coils). Because the Siemens scanner allows ~100µs for the switching to happen, this design is optimized for fairly low parts count, low off-state power, and robust design rather than switching speed.<br />
<br />
== Design files ==<br />
Design files were created in KiCAD 5<br /><br />
[[Media:PIN_driver_8x_1.1.1.zip]]<br /><br />
[[Media:PIN_driver_8x_1.2.zip]] Contains assembly files for automated assembly, through PCB Universe or another service</div>Dstraneyhttps://rflab.martinos.org/index.php?title=PIN_Diode_Driver_(8-channel)&diff=283PIN Diode Driver (8-channel)2020-06-25T22:43:14Z<p>Dstraney: </p>
<hr />
<div>== Overview ==<br />
[[File:PIN_diode_driver_8x.JPG]]<br /><br />
This PIN diode driver is intended to allow new RF coil designs to use more PIN diode channels than the Siemens scanners provide, especially for high-channel-count coil designs. Mounted to an RF coil, it takes on/off input control from an existing PIN diode line from the scanner, and drives the 8 channels in sync with the scanner's PIN diode line.<br />
<br />
== Using the drivers ==<br />
=== Connections and Power ===<br />
Power inputs are +5V @ 1A (for forward bias), and -15V @ 10 mA (for reverse-bias). Each output provides 100 mA (nominal) when on, and approx. -14.5V when off.<br />
* Protection consists of two SMT fuses, one for +5V and one for -15V, and "resettable" PTC fuses in the reverse-bias drivers.<br />
* The +5V fuse is a Schurter [https://www.digikey.com/product-detail/en/schurter-inc/3413-0219-22/486-1147-1-ND/1522979 3413.0219.22], but any 1206-size 2A fast-blow fuse will work. The -15V fuse is a Schurter [https://www.digikey.com/product-detail/en/schurter-inc/3413-0213-22/486-1141-1-ND/1522973 3413.0213.22], but any 1206-size 0.2A to 0.5A fast-blow fuse will work.<br />
* A red LED (one for each fuse) will light if power is applied and one of the power input fuses is blown. This can happen due to reversed power supply polarity/incorrect power supply connection, power supply over-voltage, or shorted outputs. The fuses can be de-soldered and new ones soldered in place; it is not worth the extra size/space, risk of eddy currents or image artifacts, etc. to use replaceable fuses as there are few opportunities to blow the fuses through user error once the PIN drivers are incorporated into a permanent setup.<br />
* Do not replace the fuses with solid jumpers! This would likely cause parts to overheat and catch on fire in case of a fault, instead of a safe blown fuse to replace.<br />
Power connections are through a 2x2 Molex Mini-Fit Jr. connector. The pinout for this connector is shown on the top-side PCB silkscreen text next to the connector pins.<br />
Input sense connections and PIN driver output connections are through soldered through-hole connections.<br />
: There are two options for connecting the sense input to a scanner PIN diode line:<br />
# In series with an existing PIN diode: populate D1 and R1, and make sure D2 is removed<br />
[[File:PIN_diode_driver_8x-conn-input-series.png]]<br />
# As a stand-alone load on the scanner's line: populate D2, and make sure D1 and R1 are removed<br />
[[File:PIN_diode_driver_8x-conn-input-direct.png]]<br />
: The sense input is electrically isolated from the rest of the circuitry and so there should be no sense connection concerns with ground loops, etc.<br />
Outputs can be combined into a single 800 mA output, by populating the 16 jumpers (0603-size) along the bottom edge of the PCB, and using the larger output through-hole connections near the bottom-left edge.<br />
<br />
=== Mechanical form factor ===<br />
See the mechanical drawing here for PCB dimensions, locations of mounting holes, and clearance needed above/below the PCB:<br />
[[Media:PIN_driver_8x-mech.pdf]]<br /><br />
The default mounting (as shown in the layout and on the silkscreen) for the Molex Mini-Fit Jr. power connector is on the bottom side of the board. However, if necessary for space constraints, this connector can also be installed on the top side of the board, or it can be left off completely (with wires soldered directly to the through-hole pads).<br />
<br />
The PIN driver can operate continuously with all channels on, at full current, without being damaged; however it does generate a reasonable amount of heat, so don't put it inside a closed box. Mounting an insulating sheet of plastic/fiberglass/etc. 10 mm above the top of the PCB is reasonable though, to keep conductive objects and dust from falling on it.<br />
<br />
=== Operation and Modifications ===<br />
'''Output current''' is not regulated, due to the difficulty of heatsinking transistors in-bore. The output current is set by driving the input +5V supply across a known resistance, into a known range of output voltages. The output current is designed to be 100 mA nominal, but will vary from 82 mA (for a 1.2V PIN diode voltage, in series with 10Ω total RF choke resistance) to 127 mA (for a 0.7V PIN diode voltage, no additional series resistance).<br />
* If the output current is higher than desired, the +5V supply can be lowered slightly. The nominal output resistance is 30Ω, so each 0.1V reduction in supply voltage will reduce output current on each channel by ~3.3 mA. Do not reduce supply voltage below 3.3V (limited by FODM8071). Reducing the +5V supply will also make the output current vary more if output voltage changes.<br />
* If the output current is lower than desired, the +5V supply can be increased slightly. Do not increase it beyond +5.4V (limited by FODM8071 optoisolator and logic inverter). Every 0.1V increase in supply voltage will increase output current on each channel by ~3.3 mA.<br />
* Output current can be increased or decreased further by increasing or decreasing the power resistor values on each channel (R24, R26, and R27 on channel 1, etc.). Do not make significant increases to the output current (>120 mA) lightly though! Many parts of the design are based around a 100 mA output current; any changes would need to account for output transistor power dissipation (MMBT2907), output transistor base current and min. beta, output resistor power dissipation and measured steady-state temperature with all channels continuously driving full current.<br />
The '''reverse-bias voltage''' has some room for adjustment:<br />
* If a lower reverse bias is desired (down to approx. -6V is possible), reduce R10's value so that it conducts about 3.5 mA or a little more.<br />
* If a higher reverse bias is desired, change or remove the 15V TVS diode D6. The largest limitation on the reverse-bias voltage is the 30V rating of the BAT54H Schottky diodes: in operation they see about 15V+5V=20V. I wouldn't recommend using any more than -20V reverse-bias. If the BAT54H parts are replaced with a similar small-signal Schottky diode with a higher voltage rating, the driver could tolerate up to -30V reverse-bias (limited by the MMBT2222 output transistors).<br />
'''Part substitutions''' are possible if some of the specific part numbers used in this design become unavailable. See "0 parts substitution notes.txt" in the design files.<br />
<br />There are inductors in series with each input power lines to serve as '''RF blocks'''; a high-impedance parallel resonant configuration was not possible due to the unexpectedly large/unpredictable parasitic capacitances. However, these still do provide some impedance at 100-300 Mhz.<br />
<br />'''Switching speed''' is slow, with up to 10µs turn-off time depending on configuration (8µs measured with a single large Macom PIN diode typically used for transmit switching in the RF Lab's coils). Because the Siemens scanner allows ~100µs for the switching to happen, this design is optimized for fairly low parts count, low off-state power, and robust design rather than switching speed.<br />
<br />
== Design files ==<br />
Design files were created in KiCAD 5<br />
[[Media:PIN_driver_8x_1.1.1.zip]]</div>Dstraneyhttps://rflab.martinos.org/index.php?title=PIN_Diode_Driver_(8-channel)&diff=280PIN Diode Driver (8-channel)2020-06-25T22:42:45Z<p>Dstraney: Added notes on switching speed</p>
<hr />
<div>== Overview ==<br />
[[File:PIN_diode_driver_8x.JPG]]<br /><br />
This PIN diode driver is intended to allow new RF coil designs to use more PIN diode channels than the Siemens scanners provide, especially for high-channel-count coil designs. Mounted to an RF coil, it takes on/off input control from an existing PIN diode line from the scanner, and drives the 8 channels in sync with the scanner's PIN diode line.<br />
<br />
== Using the drivers ==<br />
=== Connections and Power ===<br />
Power inputs are +5V @ 1A (for forward bias), and -15V @ 10 mA (for reverse-bias). Each output provides 100 mA (nominal) when on, and approx. -14.5V when off.<br />
* Protection consists of two SMT fuses, one for +5V and one for -15V, and "resettable" PTC fuses in the reverse-bias drivers.<br />
* The +5V fuse is a Schurter [https://www.digikey.com/product-detail/en/schurter-inc/3413-0219-22/486-1147-1-ND/1522979 3413.0219.22], but any 1206-size 2A fast-blow fuse will work. The -15V fuse is a Schurter [https://www.digikey.com/product-detail/en/schurter-inc/3413-0213-22/486-1141-1-ND/1522973 3413.0213.22], but any 1206-size 0.2A to 0.5A fast-blow fuse will work.<br />
* A red LED (one for each fuse) will light if power is applied and one of the power input fuses is blown. This can happen due to reversed power supply polarity/incorrect power supply connection, power supply over-voltage, or shorted outputs. The fuses can be de-soldered and new ones soldered in place; it is not worth the extra size/space, risk of eddy currents or image artifacts, etc. to use replaceable fuses as there are few opportunities to blow the fuses through user error once the PIN drivers are incorporated into a permanent setup.<br />
* Do not replace the fuses with solid jumpers! This would likely cause parts to overheat and catch on fire in case of a fault, instead of a safe blown fuse to replace.<br />
Power connections are through a 2x2 Molex Mini-Fit Jr. connector. The pinout for this connector is shown on the top-side PCB silkscreen text next to the connector pins.<br />
Input sense connections and PIN driver output connections are through soldered through-hole connections.<br />
: There are two options for connecting the sense input to a scanner PIN diode line:<br />
# In series with an existing PIN diode: populate D1 and R1, and make sure D2 is removed<br />
[[File:PIN_diode_driver_8x-conn-input-series.png]]<br />
# As a stand-alone load on the scanner's line: populate D2, and make sure D1 and R1 are removed<br />
[[File:PIN_diode_driver_8x-conn-input-direct.png]]<br />
: The sense input is electrically isolated from the rest of the circuitry and so there should be no sense connection concerns with ground loops, etc.<br />
Outputs can be combined into a single 800 mA output, by populating the 16 jumpers (0603-size) along the bottom edge of the PCB, and using the larger output through-hole connections near the bottom-left edge.<br />
<br />
=== Mechanical form factor ===<br />
See the mechanical drawing here for PCB dimensions, locations of mounting holes, and clearance needed above/below the PCB:<br />
[[Media:PIN_driver_8x-mech.pdf]]<br /><br />
The default mounting (as shown in the layout and on the silkscreen) for the Molex Mini-Fit Jr. power connector is on the bottom side of the board. However, if necessary for space constraints, this connector can also be installed on the top side of the board, or it can be left off completely (with wires soldered directly to the through-hole pads).<br />
<br />
The PIN driver can operate continuously with all channels on, at full current, without being damaged; however it does generate a reasonable amount of heat, so don't put it inside a closed box. Mounting an insulating sheet of plastic/fiberglass/etc. 10 mm above the top of the PCB is reasonable though, to keep conductive objects and dust from falling on it.<br />
<br />
=== Operation and Modifications ===<br />
'''Output current''' is not regulated, due to the difficulty of heatsinking transistors in-bore. The output current is set by driving the input +5V supply across a known resistance, into a known range of output voltages. The output current is designed to be 100 mA nominal, but will vary from 82 mA (for a 1.2V PIN diode voltage, in series with 10Ω total RF choke resistance) to 127 mA (for a 0.7V PIN diode voltage, no additional series resistance).<br />
* If the output current is higher than desired, the +5V supply can be lowered slightly. The nominal output resistance is 30Ω, so each 0.1V reduction in supply voltage will reduce output current on each channel by ~3.3 mA. Do not reduce supply voltage below 3.3V (limited by FODM8071). Reducing the +5V supply will also make the output current vary more if output voltage changes.<br />
* If the output current is lower than desired, the +5V supply can be increased slightly. Do not increase it beyond +5.4V (limited by FODM8071 optoisolator and logic inverter). Every 0.1V increase in supply voltage will increase output current on each channel by ~3.3 mA.<br />
* Output current can be increased or decreased further by increasing or decreasing the power resistor values on each channel (R24, R26, and R27 on channel 1, etc.). Do not make significant increases to the output current (>120 mA) lightly though! Many parts of the design are based around a 100 mA output current; any changes would need to account for output transistor power dissipation (MMBT2907), output transistor base current and min. beta, output resistor power dissipation and measured steady-state temperature with all channels continuously driving full current.<br />
The '''reverse-bias voltage''' has some room for adjustment:<br />
* If a lower reverse bias is desired (down to approx. -6V is possible), reduce R10's value so that it conducts about 3.5 mA or a little more.<br />
* If a higher reverse bias is desired, change or remove the 15V TVS diode D6. The largest limitation on the reverse-bias voltage is the 30V rating of the BAT54H Schottky diodes: in operation they see about 15V+5V=20V. I wouldn't recommend using any more than -20V reverse-bias. If the BAT54H parts are replaced with a similar small-signal Schottky diode with a higher voltage rating, the driver could tolerate up to -30V reverse-bias (limited by the MMBT2222 output transistors).<br />
'''Part substitutions''' are possible if some of the specific part numbers used in this design become unavailable. See "0 parts substitution notes.txt" in the design files.<br />
<br />There are inductors in series with each input power lines to serve as '''RF blocks'''; a high-impedance parallel resonant configuration was not possible due to the unexpectedly large/unpredictable parasitic capacitances. However, these still do provide some impedance at 100-300 Mhz.<br />
'''Switching speed''' is slow, with up to 10µs turn-off time depending on configuration (8µs measured with a single large Macom PIN diode typically used for transmit switching in the RF Lab's coils). Because the Siemens scanner allows ~100µs for the switching to happen, this design is optimized for fairly low parts count, low off-state power, and robust design rather than switching speed.<br />
<br />
== Design files ==<br />
Design files were created in KiCAD 5<br />
[[Media:PIN_driver_8x_1.1.1.zip]]</div>Dstraneyhttps://rflab.martinos.org/index.php?title=PIN_Diode_Driver_(8-channel)&diff=218PIN Diode Driver (8-channel)2020-03-16T23:46:50Z<p>Dstraney: </p>
<hr />
<div>== Overview ==<br />
[[File:PIN_diode_driver_8x.JPG]]<br /><br />
This PIN diode driver is intended to allow new RF coil designs to use more PIN diode channels than the Siemens scanners provide, especially for high-channel-count coil designs. Mounted to an RF coil, it takes on/off input control from an existing PIN diode line from the scanner, and drives the 8 channels in sync with the scanner's PIN diode line.<br />
<br />
== Using the drivers ==<br />
=== Connections and Power ===<br />
Power inputs are +5V @ 1A (for forward bias), and -15V @ 10 mA (for reverse-bias). Each output provides 100 mA (nominal) when on, and approx. -14.5V when off.<br />
* Protection consists of two SMT fuses, one for +5V and one for -15V, and "resettable" PTC fuses in the reverse-bias drivers.<br />
* The +5V fuse is a Schurter [https://www.digikey.com/product-detail/en/schurter-inc/3413-0219-22/486-1147-1-ND/1522979 3413.0219.22], but any 1206-size 2A fast-blow fuse will work. The -15V fuse is a Schurter [https://www.digikey.com/product-detail/en/schurter-inc/3413-0213-22/486-1141-1-ND/1522973 3413.0213.22], but any 1206-size 0.2A to 0.5A fast-blow fuse will work.<br />
* A red LED (one for each fuse) will light if power is applied and one of the power input fuses is blown. This can happen due to reversed power supply polarity/incorrect power supply connection, power supply over-voltage, or shorted outputs. The fuses can be de-soldered and new ones soldered in place; it is not worth the extra size/space, risk of eddy currents or image artifacts, etc. to use replaceable fuses as there are few opportunities to blow the fuses through user error once the PIN drivers are incorporated into a permanent setup.<br />
* Do not replace the fuses with solid jumpers! This would likely cause parts to overheat and catch on fire in case of a fault, instead of a safe blown fuse to replace.<br />
Power connections are through a 2x2 Molex Mini-Fit Jr. connector. The pinout for this connector is shown on the top-side PCB silkscreen text next to the connector pins.<br />
Input sense connections and PIN driver output connections are through soldered through-hole connections.<br />
: There are two options for connecting the sense input to a scanner PIN diode line:<br />
# In series with an existing PIN diode: populate D1 and R1, and make sure D2 is removed<br />
[[File:PIN_diode_driver_8x-conn-input-series.png]]<br />
# As a stand-alone load on the scanner's line: populate D2, and make sure D1 and R1 are removed<br />
[[File:PIN_diode_driver_8x-conn-input-direct.png]]<br />
: The sense input is electrically isolated from the rest of the circuitry and so there should be no sense connection concerns with ground loops, etc.<br />
Outputs can be combined into a single 800 mA output, by populating the 16 jumpers (0603-size) along the bottom edge of the PCB, and using the larger output through-hole connections near the bottom-left edge.<br />
<br />
=== Mechanical form factor ===<br />
See the mechanical drawing here for PCB dimensions, locations of mounting holes, and clearance needed above/below the PCB:<br />
[[Media:PIN_driver_8x-mech.pdf]]<br /><br />
The default mounting (as shown in the layout and on the silkscreen) for the Molex Mini-Fit Jr. power connector is on the bottom side of the board. However, if necessary for space constraints, this connector can also be installed on the top side of the board, or it can be left off completely (with wires soldered directly to the through-hole pads).<br />
<br />
The PIN driver can operate continuously with all channels on, at full current, without being damaged; however it does generate a reasonable amount of heat, so don't put it inside a closed box. Mounting an insulating sheet of plastic/fiberglass/etc. 10 mm above the top of the PCB is reasonable though, to keep conductive objects and dust from falling on it.<br />
<br />
=== Operation and Modifications ===<br />
'''Output current''' is not regulated, due to the difficulty of heatsinking transistors in-bore. The output current is set by driving the input +5V supply across a known resistance, into a known range of output voltages. The output current is designed to be 100 mA nominal, but will vary from 82 mA (for a 1.2V PIN diode voltage, in series with 10Ω total RF choke resistance) to 127 mA (for a 0.7V PIN diode voltage, no additional series resistance).<br />
* If the output current is higher than desired, the +5V supply can be lowered slightly. The nominal output resistance is 30Ω, so each 0.1V reduction in supply voltage will reduce output current on each channel by ~3.3 mA. Do not reduce supply voltage below 3.3V (limited by FODM8071). Reducing the +5V supply will also make the output current vary more if output voltage changes.<br />
* If the output current is lower than desired, the +5V supply can be increased slightly. Do not increase it beyond +5.4V (limited by FODM8071 optoisolator and logic inverter). Every 0.1V increase in supply voltage will increase output current on each channel by ~3.3 mA.<br />
* Output current can be increased or decreased further by increasing or decreasing the power resistor values on each channel (R24, R26, and R27 on channel 1, etc.). Do not make significant increases to the output current (>120 mA) lightly though! Many parts of the design are based around a 100 mA output current; any changes would need to account for output transistor power dissipation (MMBT2907), output transistor base current and min. beta, output resistor power dissipation and measured steady-state temperature with all channels continuously driving full current.<br />
The '''reverse-bias voltage''' has some room for adjustment:<br />
* If a lower reverse bias is desired (down to approx. -6V is possible), reduce R10's value so that it conducts about 3.5 mA or a little more.<br />
* If a higher reverse bias is desired, change or remove the 15V TVS diode D6. The largest limitation on the reverse-bias voltage is the 30V rating of the BAT54H Schottky diodes: in operation they see about 15V+5V=20V. I wouldn't recommend using any more than -20V reverse-bias. If the BAT54H parts are replaced with a similar small-signal Schottky diode with a higher voltage rating, the driver could tolerate up to -30V reverse-bias (limited by the MMBT2222 output transistors).<br />
'''Part substitutions''' are possible if some of the specific part numbers used in this design become unavailable. See "0 parts substitution notes.txt" in the design files.<br />
<br />There are inductors in series with each input power lines to serve as '''RF blocks'''; a high-impedance parallel resonant configuration was not possible due to the unexpectedly large/unpredictable parasitic capacitances. However, these still do provide some impedance at 100-300 Mhz.<br />
<br />
== Design files ==<br />
Design files were created in KiCAD 5<br />
[[Media:PIN_driver_8x_1.1.1.zip]]</div>Dstraneyhttps://rflab.martinos.org/index.php?title=PIN_Diode_Driver_(8-channel)&diff=215PIN Diode Driver (8-channel)2020-03-16T23:43:39Z<p>Dstraney: first draft content for all sections</p>
<hr />
<div>== Overview ==<br />
[[File:PIN_diode_driver_8x.JPG]]<br /><br />
This PIN diode driver is intended to allow new RF coil designs to use more PIN diode channels than the Siemens scanners provide, especially for high-channel-count coil designs. Mounted to an RF coil, it takes on/off input control from an existing PIN diode line from the scanner, and drives the 8 channels in sync with the scanner's PIN diode line.<br />
<br />
== Using the drivers ==<br />
=== Connections and Power ===<br />
Power inputs are +5V @ 1A (for forward bias), and -15V @ 10 mA (for reverse-bias). Each output provides 100 mA (nominal) when on, and approx. -14.5V when off.<br />
* Protection consists of two SMT fuses, one for +5V and one for -15V, and "resettable" PTC fuses in the reverse-bias drivers.<br />
* The +5V fuse is a Schurter [https://www.digikey.com/product-detail/en/schurter-inc/3413-0219-22/486-1147-1-ND/1522979 3413.0219.22], but any 1206-size 2A fast-blow fuse will work. The -15V fuse is a Schurter [https://www.digikey.com/product-detail/en/schurter-inc/3413-0213-22/486-1141-1-ND/1522973 3413.0213.22], but any 1206-size 0.2A to 0.5A fast-blow fuse will work.<br />
* A red LED (one for each fuse) will light if power is applied and one of the power input fuses is blown. This can happen due to reversed power supply polarity/incorrect power supply connection, power supply over-voltage, or shorted outputs. The fuses can be de-soldered and new ones soldered in place (see BOM for part numbers); it is not worth the extra size/space, risk of eddy currents or image artifacts, etc. to use replaceable fuses as there are few opportunities to blow the fuses through user error once the PIN drivers are incorporated into a permanent setup.<br />
* Do not replace the fuses with solid jumpers! This would likely cause parts to overheat and catch on fire in case of a fault, instead of a safe blown fuse to replace.<br />
Power connections are through a 2x2 Molex Mini-Fit Jr. connector. The pinout for this connector is shown on the top-side PCB silkscreen text next to the connector pins.<br />
Input sense connections and PIN driver output connections are through soldered through-hole connections.<br />
: There are two options for connecting the sense input to a scanner PIN diode line:<br />
# In series with an existing PIN diode: populate D1 and R1, and make sure D2 is removed<br />
[[File:PIN_diode_driver_8x-conn-input-series.png]]<br />
# As a stand-alone load on the scanner's line: populate D2, and make sure D1 and R1 are removed<br />
[[File:PIN_diode_driver_8x-conn-input-direct.png]]<br />
: The sense input is electrically isolated from the rest of the circuitry and so there should be no sense connection concerns with ground loops, etc.<br />
Outputs can be combined into a single 800 mA output, by populating the 16 jumpers (0603-size) along the bottom edge of the PCB, and using the larger output through-hole connections near the bottom-left edge.<br />
<br />
=== Mechanical form factor ===<br />
See the mechanical drawing here for PCB dimensions, locations of mounting holes, and clearance needed above/below the PCB:<br />
[[Media:PIN_driver_8x-mech.pdf]]<br /><br />
The default mounting (as shown in the layout and on the silkscreen) for the Molex Mini-Fit Jr. power connector is on the bottom side of the board. However, if necessary for space constraints, this connector can also be installed on the top side of the board, or it can be left off completely (with wires soldered directly to the through-hole pads).<br />
<br />
The PIN driver can operate continuously with all channels on, at full current, without being damaged; however it does generate a reasonable amount of heat, so don't put it inside a closed box. Mounting an insulating sheet of plastic/fiberglass/etc. 10 mm above the top of the PCB is reasonable though, to keep conductive objects and dust from falling on it.<br />
<br />
=== Operation and Modifications ===<br />
'''Output current''' is not regulated, due to the difficulty of heatsinking transistors in-bore. The output current is set by driving the input +5V supply across a known resistance, into a known range of output voltages. The output current is designed to be 100 mA nominal, but will vary from 82 mA (for a 1.2V PIN diode voltage, in series with 10Ω total RF choke resistance) to 127 mA (for a 0.7V PIN diode voltage, no additional series resistance).<br />
* If the output current is higher than desired, the +5V supply can be lowered slightly. The nominal output resistance is 30Ω, so each 0.1V reduction in supply voltage will reduce output current on each channel by ~3.3 mA. Do not reduce supply voltage below 3.3V (limited by FODM8071). Reducing the +5V supply will also make the output current vary more if output voltage changes.<br />
* If the output current is lower than desired, the +5V supply can be increased slightly. Do not increase it beyond +5.4V (limited by FODM8071 optoisolator and logic inverter). Every 0.1V increase in supply voltage will increase output current on each channel by ~3.3 mA.<br />
* Output current can be increased or decreased further by increasing or decreasing the power resistor values on each channel (R24, R26, and R27 on channel 1, etc.). Do not make significant increases to the output current (>120 mA) lightly though! Many parts of the design are based around a 100 mA output current; any changes would need to account for output transistor power dissipation (MMBT2907), output transistor base current and min. beta, output resistor power dissipation and measured steady-state temperature with all channels continuously driving full current.<br />
The '''reverse-bias voltage''' has some room for adjustment:<br />
* If a lower reverse bias is desired (down to approx. -6V is possible), reduce R10's value so that it conducts about 3.5 mA or a little more.<br />
* If a higher reverse bias is desired, change or remove the 15V TVS diode D6. The largest limitation on the reverse-bias voltage is the 30V rating of the BAT54H Schottky diodes: in operation they see about 15V+5V=20V. I wouldn't recommend using any more than -20V reverse-bias. If the BAT54H parts are replaced with a similar small-signal Schottky diode with a higher voltage rating, the driver could tolerate up to -30V reverse-bias (limited by the MMBT2222 output transistors).<br />
'''Part substitutions''' are possible if some of the specific part numbers used in this design become unavailable. See "0 parts substitution notes.txt" in the design files.<br />
There are inductors in series with each input power lines to serve as '''RF blocks'''; a high-impedance parallel resonant configuration was not possible due to the unexpectedly large/unpredictable parasitic capacitances. However, these still do provide some impedance at 100-300 Mhz.<br />
<br />
== Design files ==<br />
Design files were created in KiCAD 5<br />
[[Media:PIN_driver_8x_1.1.1.zip]]</div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:PIN_driver_8x_1.1.1.zip&diff=212File:PIN driver 8x 1.1.1.zip2020-03-16T23:35:15Z<p>Dstraney: PIN diode driver (8x) design files, version 1.1.1</p>
<hr />
<div>PIN diode driver (8x) design files, version 1.1.1</div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:PIN_diode_driver_8x-conn-input-direct.png&diff=209File:PIN diode driver 8x-conn-input-direct.png2020-03-16T23:00:46Z<p>Dstraney: Dstraney uploaded a new version of File:PIN diode driver 8x-conn-input-direct.png</p>
<hr />
<div>Sense input connection diagram for PIN diode driver (8-channel); in series with existing PIN diode</div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:PIN_diode_driver_8x-conn-input-series.png&diff=206File:PIN diode driver 8x-conn-input-series.png2020-03-16T22:59:52Z<p>Dstraney: Sense input connection diagram for PIN diode driver (8-channel); in series with existing PIN diode</p>
<hr />
<div>Sense input connection diagram for PIN diode driver (8-channel); in series with existing PIN diode</div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:PIN_diode_driver_8x-conn-input-direct.png&diff=203File:PIN diode driver 8x-conn-input-direct.png2020-03-16T22:59:30Z<p>Dstraney: Sense input connection diagram for PIN diode driver (8-channel); in series with existing PIN diode</p>
<hr />
<div>Sense input connection diagram for PIN diode driver (8-channel); in series with existing PIN diode</div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:PIN_driver_8x-mech.pdf&diff=200File:PIN driver 8x-mech.pdf2020-03-16T22:23:14Z<p>Dstraney: PIN diode driver (8-channel): mechanical outline and mounting hole drawing</p>
<hr />
<div>PIN diode driver (8-channel): mechanical outline and mounting hole drawing</div>Dstraneyhttps://rflab.martinos.org/index.php?title=File:PIN_diode_driver_8x.JPG&diff=197File:PIN diode driver 8x.JPG2020-03-16T21:48:10Z<p>Dstraney: PIN diode driver (8-channel), version 1.1, with shared/ganged single output option populated</p>
<hr />
<div>PIN diode driver (8-channel), version 1.1, with shared/ganged single output option populated</div>Dstraneyhttps://rflab.martinos.org/index.php?title=Main_Page&diff=194Main Page2020-03-06T14:49:06Z<p>Dstraney: /* Resources */</p>
<hr />
<div>== Radio Frequency Laboratory of the Wald Group at MGH ==<br />
<br />
This page contains resources for RF coil design, fabrication, and testing related to the work conducted in the RF Lab of Dr. Lawrence Wald's group at the A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston, MA, USA. <br />
<br />
<br />
''NEW (July 2019): Revision C of the open-source shim amplifier are now available online. Please see Current driver section below.'' <br />
<br />
<br />
''NEW (July 2016): MATLAB code is now available for multi-coil shimming simulations. The code includes helmet-style wire patterns and a constrained optimization script for finding optimal shim currents for B0 shimming of the brain. Please see the'' [[Multi-coil B0 shimming]] ''section below.'' <br />
<br />
<br />
<br />
''This page is under construction -- thank you for your patience as we upload materials...'' <br />
<br />
<br />
<br />
== Resources ==<br />
* [[Current driver:Current driver|Multi-channel current driver board]]<br />
<br />
* [[Multi-coil B0 shimming|Multi-coil B0 shimming research methods]]<br />
<br />
* [[Information and How-To guides for building RF coils]]<br />
<br />
* [[PIN Diode Driver (8-channel)]]<br />
<br />
== Links to other Wikis in the Wald Group ==<br />
<br />
* [http://phantoms.martinos.org/Main_Page Link to anthropomorphic phantom wiki]<br />
* [http://ptx.martinos.org Link to pTx wiki]<br />
* [http://tabletop.martinos.org Link to tabletop educational MRI scanner wiki]<br />
* [http://mpi.martinos.org Link to Magnetic Particle Imaging (MPI) wiki]</div>Dstraneyhttps://rflab.martinos.org/index.php?title=PIN_Diode_Driver_(8-channel)&diff=191PIN Diode Driver (8-channel)2020-03-06T14:48:20Z<p>Dstraney: Usage, repair, and build information for 8-channel PIN diode drivers</p>
<hr />
<div>== Overview ==<br />
<br />
== Using the drivers ==<br />
<br />
<br />
== Repair notes ==<br />
<br />
<br />
== Design files ==</div>Dstraney