Hardware:GPA - Revision history

LincolnCB: /* 3ch GPA using 8ch Shim Board */

2020-09-29T17:29:12Z

3ch GPA using 8ch Shim Board

← Older revision		Revision as of 13:29, 29 September 2020
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	</gallery>		</gallery>

	The Rev C shim board requires a tuned compensation feedback loop to avoid signal ringing. This is dependent on the load -- for the Halbach scanner, the feedback capacitors are currently 1470 pF. This requires switching out components to change.		The Rev C shim board requires a tuned compensation feedback loop to avoid signal ringing. This is dependent on the load -- for the Halbach scanner, a tabletop MR scanner with ~400 uH coil inductance and ~2 Ohm resistance, the feedback capacitors are currently 1470 pF. This requires switching out components to change.

	[[Media:buffer_board.zip\|Buffer board KiCAD files]]		[[Media:buffer_board.zip\|Buffer board KiCAD files]]

LincolnCB: /* 3ch GPA using 8ch Shim Board */

2020-09-29T17:17:53Z

3ch GPA using 8ch Shim Board

← Older revision		Revision as of 13:17, 29 September 2020
Line 118:		Line 118:
	The Rev C shim board requires a tuned compensation feedback loop to avoid signal ringing. This is dependent on the load -- for the Halbach scanner, the feedback capacitors are currently 1470 pF. This requires switching out components to change.		The Rev C shim board requires a tuned compensation feedback loop to avoid signal ringing. This is dependent on the load -- for the Halbach scanner, the feedback capacitors are currently 1470 pF. This requires switching out components to change.

	[[Media:buffer_board.zip]]		[[Media:buffer_board.zip\|Buffer board KiCAD files]]

LincolnCB: /* 3ch GPA using 8ch Shim Board */

2020-09-29T17:16:34Z

3ch GPA using 8ch Shim Board

← Older revision		Revision as of 13:16, 29 September 2020
Line 117:		Line 117:

	The Rev C shim board requires a tuned compensation feedback loop to avoid signal ringing. This is dependent on the load -- for the Halbach scanner, the feedback capacitors are currently 1470 pF. This requires switching out components to change.		The Rev C shim board requires a tuned compensation feedback loop to avoid signal ringing. This is dependent on the load -- for the Halbach scanner, the feedback capacitors are currently 1470 pF. This requires switching out components to change.

			[[Media:buffer_board.zip]]

LincolnCB: /* 3ch GPA using 8ch Shim Board */

2020-09-29T17:13:48Z

3ch GPA using 8ch Shim Board

← Older revision		Revision as of 13:13, 29 September 2020
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	<gallery widths="350px" heights="250px">		<gallery widths="350px" heights="250px">
	image:3ch_buffer_placement.jpg\|Buffer board placed on shim amplifier pcb		image:3ch_buffer_placement.jpg\|Buffer board placed on shim amplifier pcb
	image:~~buffer_layout~~.png\|Buffer board pcb layout		image:buffer_pcb.png\|Buffer board pcb layout
	image:buffer_schematic.png\|Buffer board schematic, containing input and current sense output buffers		image:buffer_schematic.png\|Buffer board schematic, containing input and current sense output buffers
	image:buffer_input_schematic.png\|Input buffer, passing the input through a unity-gain buffer		image:buffer_input_schematic.png\|Input buffer, passing the input through a unity-gain buffer

LincolnCB: /* 3ch GPA using 8ch Shim Board */

2020-09-29T17:11:56Z

3ch GPA using 8ch Shim Board

← Older revision		Revision as of 13:11, 29 September 2020
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	== 3ch GPA using 8ch Shim Board ==		== 3ch GPA using 8ch Shim Board ==
	Using the existing Rev C shim amplifier board, this GPA gives 3 channels of 8+ Amps of current. Channels X and Z have a gain of 5.5 A/V, and channel Y has a gain of 3.75 A/V. The GPA is powered with two series 24V supplies. Three BNC connectors take voltage waveform inputs at audio frequencies output to three banana plug outputs. An ammeter tracks total current use for the board, ~~and there~~ are current sense pins available per channel at 1 V/A.		Using the existing Rev C shim amplifier board, this GPA gives 3 channels of 8+ Amps of current. Channels X and Z have a gain of 5.5 A/V, and channel Y has a gain of 3.75 A/V. The GPA is powered with two series 24V supplies. Three BNC connectors take voltage waveform inputs at audio frequencies output to three banana plug outputs. An ammeter tracks total current use for the board, with a typical quiescent current of 600 mA. There are current sense pins available per channel at 1 V/A.
	[[File:3ch_gpa.jpg\|300px\|thumb\|right\|3ch gradient amplifier built from a modified 8ch shim amplifier board]]		[[File:3ch_gpa.jpg\|300px\|thumb\|right\|3ch gradient amplifier built from a modified 8ch shim amplifier board]]

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	</gallery>		</gallery>

	To use the Rev C shim amplifier board, the GPA groups channels together (3 for X, Z, 2 for Y) to raise current limits. The shim pcb is fitted with an additional buffer board that attaches on top of it. The buffer board buffers the inputs and current sense outputs to avoid grounding issues.		To use the Rev C shim amplifier board, the GPA groups channels together (3 for X, Z, 2 for Y) to raise current limits. The shim pcb is fitted with an additional buffer board that attaches on top of it. The buffer board buffers the inputs and current sense outputs to avoid grounding issues. The inputs and outputs to the buffer board are wires that are jumped onto the board.

	<gallery widths="350px" heights="250px">		<gallery widths="350px" heights="250px">
	image:3ch_buffer_placement.jpg\|Buffer board placed on shim amplifier pcb		image:3ch_buffer_placement.jpg\|Buffer board placed on shim amplifier pcb
	image:buffer_schematic.png\|Buffer board schematic -- one section passes the input through a unity-gain buffer, while the other adds the current sense resistor voltage drops to a gain of 1 V/A per channel (X, Y, Z).
	image:buffer_layout.png\|Buffer board pcb layout		image:buffer_layout.png\|Buffer board pcb layout
			image:buffer_schematic.png\|Buffer board schematic, containing input and current sense output buffers
			image:buffer_input_schematic.png\|Input buffer, passing the input through a unity-gain buffer
			image:buffer_current_sense.png\|Current sense voltage adder and buffer, tracking the current sense resistor voltage drops to a gain of 1 V/A per channel (X, Y, Z)
	</gallery>		</gallery>

	The Rev C shim board requires a tuned compensation feedback loop to avoid signal ringing. This is dependent on the load -- for the Halbach scanner, the feedback capacitors are currently 1470 pF. This requires switching out components to change.		The Rev C shim board requires a tuned compensation feedback loop to avoid signal ringing. This is dependent on the load -- for the Halbach scanner, the feedback capacitors are currently 1470 pF. This requires switching out components to change.

LincolnCB: /* 3ch GPA using 8ch Shim Board */

2020-09-29T17:05:52Z

3ch GPA using 8ch Shim Board

← Older revision		Revision as of 13:05, 29 September 2020
Line 109:		Line 109:

	<gallery widths="350px" heights="250px">		<gallery widths="350px" heights="250px">
			image:3ch_buffer_placement.jpg\|Buffer board placed on shim amplifier pcb
	image:buffer_schematic.png\|Buffer board schematic -- one section passes the input through a unity-gain buffer, while the other adds the current sense resistor voltage drops to a gain of 1 V/A per channel (X, Y, Z).		image:buffer_schematic.png\|Buffer board schematic -- one section passes the input through a unity-gain buffer, while the other adds the current sense resistor voltage drops to a gain of 1 V/A per channel (X, Y, Z).
	image:buffer_layout.png\|Buffer board pcb layout		image:buffer_layout.png\|Buffer board pcb layout

LincolnCB: /* 3ch GPA using 8ch Shim Board */

2020-09-29T17:04:55Z

3ch GPA using 8ch Shim Board

← Older revision		Revision as of 13:04, 29 September 2020
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	<gallery widths="350px" heights="250px">		<gallery widths="350px" heights="250px">
	image:3ch_inputs.jpg\|3 BNC ports (X, Y, Z) take differential voltage waves and output 8+ Amps from 3 banana plug outputs		image:3ch_inputs.jpg\|3 BNC ports (X, Y, Z) take differential voltage waves and output 8+ Amps from 3 banana plug outputs
	image:~~3ch_inside~~.jpg\|The Rev C shim amplifier board is modified with a buffer on the input and output, along with ganging channels together to raise current limits (3 channels for X, Z; 2 for Y)		image:3ch_insides.jpg\|The Rev C shim amplifier board is modified with a buffer on the input and output, along with ganging channels together to raise current limits (3 channels for X, Z; 2 for Y)
	</gallery>		</gallery>

LincolnCB at 17:04, 29 September 2020

2020-09-29T17:04:38Z

← Older revision		Revision as of 13:04, 29 September 2020
Line 99:		Line 99:
	== 3ch GPA using 8ch Shim Board ==		== 3ch GPA using 8ch Shim Board ==
	Using the existing Rev C shim amplifier board, this GPA gives 3 channels of 8+ Amps of current. Channels X and Z have a gain of 5.5 A/V, and channel Y has a gain of 3.75 A/V. The GPA is powered with two series 24V supplies. Three BNC connectors take voltage waveform inputs at audio frequencies output to three banana plug outputs. An ammeter tracks total current use for the board, and there are current sense pins available per channel at 1 V/A.		Using the existing Rev C shim amplifier board, this GPA gives 3 channels of 8+ Amps of current. Channels X and Z have a gain of 5.5 A/V, and channel Y has a gain of 3.75 A/V. The GPA is powered with two series 24V supplies. Three BNC connectors take voltage waveform inputs at audio frequencies output to three banana plug outputs. An ammeter tracks total current use for the board, and there are current sense pins available per channel at 1 V/A.
	[[File:~~3ch_GPA_box~~.~~PNG~~\|300px\|thumb\|right\|3ch gradient amplifier built from a modified 8ch shim amplifier board]]		[[File:3ch_gpa.jpg\|300px\|thumb\|right\|3ch gradient amplifier built from a modified 8ch shim amplifier board]]

	<gallery widths="350px" heights="250px">		<gallery widths="350px" heights="250px">
	image:3ch_inputs.~~png~~\|3 BNC ports (X, Y, Z) take differential voltage waves and output 8+ Amps from 3 banana plug outputs		image:3ch_inputs.jpg\|3 BNC ports (X, Y, Z) take differential voltage waves and output 8+ Amps from 3 banana plug outputs
	image:3ch_inside.~~png~~\|The Rev C shim amplifier board is modified with a buffer on the input and output, along with ganging channels together to raise current limits (3 channels for X, Z; 2 for Y)		image:3ch_inside.jpg\|The Rev C shim amplifier board is modified with a buffer on the input and output, along with ganging channels together to raise current limits (3 channels for X, Z; 2 for Y)
	</gallery>		</gallery>

LincolnCB at 16:57, 29 September 2020

2020-09-29T16:57:08Z

← Older revision		Revision as of 12:57, 29 September 2020
Line 96:		Line 96:

	[[File:gradient_filter_photo.png\|400px\|thumb\|none\|Sample of populated filter board (v1)]]		[[File:gradient_filter_photo.png\|400px\|thumb\|none\|Sample of populated filter board (v1)]]

			== 3ch GPA using 8ch Shim Board ==
			Using the existing Rev C shim amplifier board, this GPA gives 3 channels of 8+ Amps of current. Channels X and Z have a gain of 5.5 A/V, and channel Y has a gain of 3.75 A/V. The GPA is powered with two series 24V supplies. Three BNC connectors take voltage waveform inputs at audio frequencies output to three banana plug outputs. An ammeter tracks total current use for the board, and there are current sense pins available per channel at 1 V/A.
			[[File:3ch_GPA_box.PNG\|300px\|thumb\|right\|3ch gradient amplifier built from a modified 8ch shim amplifier board]]

			<gallery widths="350px" heights="250px">
			image:3ch_inputs.png\|3 BNC ports (X, Y, Z) take differential voltage waves and output 8+ Amps from 3 banana plug outputs
			image:3ch_inside.png\|The Rev C shim amplifier board is modified with a buffer on the input and output, along with ganging channels together to raise current limits (3 channels for X, Z; 2 for Y)
			</gallery>

			To use the Rev C shim amplifier board, the GPA groups channels together (3 for X, Z, 2 for Y) to raise current limits. The shim pcb is fitted with an additional buffer board that attaches on top of it. The buffer board buffers the inputs and current sense outputs to avoid grounding issues.

			<gallery widths="350px" heights="250px">
			image:buffer_schematic.png\|Buffer board schematic -- one section passes the input through a unity-gain buffer, while the other adds the current sense resistor voltage drops to a gain of 1 V/A per channel (X, Y, Z).
			image:buffer_layout.png\|Buffer board pcb layout
			</gallery>

			The Rev C shim board requires a tuned compensation feedback loop to avoid signal ringing. This is dependent on the load -- for the Halbach scanner, the feedback capacitors are currently 1470 pF. This requires switching out components to change.

Jaystock: /* Version 1 of the GPA board */

2020-05-28T16:49:39Z

Version 1 of the GPA board

← Older revision		Revision as of 12:49, 28 May 2020
Line 14:		Line 14:
	A summing point op amp is used to compare the current sense resistor voltage to the input signal in order to adjust the output stage as needed. The current sensor consists of an [http://www.ti.com/lit/ds/symlink/ina105.pdf INA105] differential amplifier that measures the voltage across a small (0.1 ohm) resistor in series with the output. A differential amplifier on the INA105 output provides a differential signal that can be scoped to monitor the current sense resistor voltage.		A summing point op amp is used to compare the current sense resistor voltage to the input signal in order to adjust the output stage as needed. The current sensor consists of an [http://www.ti.com/lit/ds/symlink/ina105.pdf INA105] differential amplifier that measures the voltage across a small (0.1 ohm) resistor in series with the output. A differential amplifier on the INA105 output provides a differential signal that can be scoped to monitor the current sense resistor voltage.

	[[File:~~Mit_gpa_schematic_V3~~.png\|300px\|thumb\|right\|Version 1 Gradient Power Amplifier circuit providing a single channel of output current]]		[[File:updated_gpa_schematic_corrected_july_2020.png\|300px\|thumb\|right\|Version 1 Gradient Power Amplifier circuit providing a single channel of output current]]

	[https://tabletop.martinos.org/images/3/32/MIT-GPA-v4.sch.pdf Click here] to view the schematic for the GPA boards generated in Eagle (version 6). Note that a separate A/D converter was used in the initial realization of the boards (DAC on the GPAs was not populated).		[https://tabletop.martinos.org/images/3/32/MIT-GPA-v4.sch.pdf Click here] to view the schematic for the GPA boards generated in Eagle (version 6). Note that a separate A/D converter was used in the initial realization of the boards (DAC on the GPAs was not populated).

← Older revision		Revision as of 13:13, 29 September 2020
Line 110:		Line 110:
	<gallery widths="350px" heights="250px">		<gallery widths="350px" heights="250px">
	image:3ch_buffer_placement.jpg\|Buffer board placed on shim amplifier pcb		image:3ch_buffer_placement.jpg\|Buffer board placed on shim amplifier pcb
	image:~~buffer_layout~~.png\|Buffer board pcb layout		image:buffer_pcb.png\|Buffer board pcb layout
	image:buffer_schematic.png\|Buffer board schematic, containing input and current sense output buffers		image:buffer_schematic.png\|Buffer board schematic, containing input and current sense output buffers
	image:buffer_input_schematic.png\|Input buffer, passing the input through a unity-gain buffer		image:buffer_input_schematic.png\|Input buffer, passing the input through a unity-gain buffer