SET DC Curve Tracer System Definition ------------------------------------------ Original Rev. 5-Jan-2020 Current Rev. 25-Feb-2020 The intent is to build a "stand alone" test system of the SET DC Curve Tracer but to make its components so that they can be moved over to the real cryostat with little or no modification. This test system will be used to "prove" that measurement of the DC operation of the SET transistor will be possible in the real cryostat and to test how well this electronics works by measuring: - Amplifier Noise Figure as determined from the RMS Noise level with the SET test resistor operating at two temperatures - Amplifier Linearity by checking the SET "V" and "I" channels against known steps in the SET Source-Drain Bias voltage - Amplifier DC Common Mode Rejection by checking the SET "V" and "I" channels against known steps in the SET S-D Bias voltage Offset - Amplifier Zero Drift by checking the SET SET "V" and "I" channels over time and against changes in temperature. An important aspect of the SET DC Curve Tracer electronics is that by using a 50k Ohm resistor in place of the SET then this electronics system can be tested without any other modification. List of components in the SET DC Curve Tracer system: 1. Instrumentation Amplifiers inside Cryostat with the associated precision resistors and required cables and mounting brackets. 2. KF Flange Cover Plate over the instrument amps with its Fischer electrical vacuum feedthrough connector. 3. Amplifier Power & SET Bias Filter Box mounted next to the SET Inst Amp Port on the cryostat. Flexible ground straps are needed between the SET Inst Amp Port and this Power/Bias Filter Box. This Power/Bias Filter Box needs to be mechanically mounted to the top of the cryostat. This box contains the fully isolated power supply and power filters for the internal Instrument Amps and contains the SET Bias Supply Filters along with their connections that run over to the external SET Bias "Voltage" and "Offset" power supplies. 4. Signal Filter Box This box is located somewhere on top of the cryostat (within a couple of feet of the Amplifier Power & SET Bias Filter Box) and is mounted to some mechanical structure that provides a direct electrical connection to the large cryostat head plate. The Signal Filter Box holds the 1 Hz and 100 Hz filters for both the SET Voltage and Current signal channels. Also included in the Signal Filter Box are the fully isolated power supplies for these signal filters. 5. Isolated Power Source Box which contains the isolated multiple outlet 25 kHz 25 Vpp power source. This box can be remotely located. This box will need a ground connection to the large cryostat head plate. The following are the more detailed descriptions and open questions about each of these components: 1. Internal Instrumentation Amplifiers & associated components: The details of the SET Instrument Amplifiers inside the cryostat are shown in the schematic and layout drawings. Noise analysis indicates that in a properly designed system the noise level should be low enough to observe the DC operation of the SET transistor. The current size of the internal Instrument Amp circuit board is 31 mm x 19 mm and about 6 mm thick. Separate circuit boards are needed for the SET V & I channels. The components associated with the SET Instrument Amps inside the cryostat are: 3 stable precision resistors, wires to the vacuum feedthrough connector, twisted pair cable (with a separation connector ???) that runs down to the SET transistor, and mounting brackets to hold the Inst Amps to the KF flange cover plate. The cryostat uses KF flanges and the pipe stub for the SET Instrumentation Amplifier Port is about ??? mm long. Total Heat of the Instrumentation Amplifiers inside the cryostat is expected to be 660 mW. This assumes that the SET Bias Offset range will be +- 3V or less, i.e. that we can operate the Inst Amps from +- 10V supplies. These Instrumentation Amplifiers will work best at about -10 to -55 deg C. The test cryostat will be used to verify that this environment is possible in the location directly under a flange cover. Each Instrumentation Amplifier circuit board includes a thermistor with 1% calibration to measure the operating temperature of these amplifiers. These measurements will be made during an engineering study and are not part of normal operation in the real cryostat. 2. KF Flange Cover Plate over the Instrument Amps with its Fischer electrical vacuum feedthrough connector: The SET Inst Amp Port uses a KF flange that is 55 mm OD with a pipe stub that is 40 mm ID. This pipe stub is about ??? mm long. Fischer hermetic connectors will be used for the electrical vacuum feedthrough. The current plan is to use a style "S" plug with style: DEE, DBEE, or DBPLE receptacle in the 104 size with 16 pins. Is an RF Filter needed at the feedthrough ??? Total Number of Electrical Feedthroughs: 2 for output signal from Instrumentation Amps 2 for OpAmp power 2 for OpAmp Power Returns 2 for SET Bias 4 for Grounds (can one make internal Gnd connections ???) 2 for Thermometer on one of the Inst Amp pcbs ??? Total about 14 electrical feedthroughs The question about making good internal Gnd connections is part of the overall issue of making Ground connections to the Cryostat in the area of the SET Instrument Amp Port. I currently assume that we can NOT make internal ground connections for the Instrument Amplifiers. The Fischer vacuum feedthrough and all components on the Inst Amp boards need to work with the 10E-5 mBar vacuum in this part of the cryostat. 3. Amplifier Power & SET Bias Filter Box: The Amplifier Power & SET Bias Filter Box needs to be mounted very close to the SET Inst Amp Port on the cryostat. This box is approximately 8" x 6" x 2.5" in size. This Power/Bias Filter Box has no Controls or Indicators. Because this Power/Bias Filter Box is not bolted to the SET Inst Amp Port it will be necessary to run ground straps from the SET Inst Amp Port for the short distance over to this Power/Bias Filter Box. Filters for all signals going into the cryostat are of a two stage design: a rough and then a fine filters with separate ground connections to the cryostat for each stage. The Amplifier Power & SET Bias Filter Box holds the fully isolated power supply for the SET Instrumentation Amplifiers. This box receives isolated 25 kHz power as its raw input and makes the clean isolated DC power for the Instrument Amps. This box provides the connections for the cables that run over to the external SET Bias Voltage and Offset power supplies. The SET V & I signals, i.e. the Inst Amp outputs, pass through this Power/Bias Filter Box on their way to the Signal Filter Box. List of Ground connections that need to be made to the SET Instrumentation Amplifier Port / Cryostat Head: 2 for the SET Bias Supply Guard connections 1 for the SET Bias Offset Supply Low Side connection 2 for the SET Bias Supply Cable Shields connections 1 for the SET Bias Supply Chassis/Rack connection 1 for the SET Bias Filter Low Side Clamp connection 2 for the SET Bias Rough Filter connections 2 for the SET Bias Fine Filter connections 1 for the Inst Amp Power Filter Ground connection 2 for the Inst Amp Power Filter Clean Ground connections 2 for the Inst Amp Reference Common connections 2 for the Inst Amp Ground connections 2 for the Signal Filter Input Reference connections 2 for the Signal Filter Output Reference connections 2 for the Signal Filter Ground connections 1 for the 25 kHz Power Source Ground connection My current understanding about SET Bias Voltage and Offset: You need to be able to operate the SET transistor in both the DC mode and in a Lock-In Detection mode. You will need to make changes in the SET Bias Voltage and Offset at different rates for these two modes and thus the SET Bias Filters need to provide different cutoff frequencies for these two different modes. Specifically: - For Lock-In operation the SET S-D Voltage will need to include about a 100 Hz sin wave and you will need to be able to change the SET S-D Offset from Ground at about 1 Hz. ??? - For DC (aka DVM operation) you will need to be able to change the SET S-D Voltage at about 1 Hz and also need to change the SET S-D Offset from Ground at about 1 Hz. ?? This SET Bias Filter cutoff frequency is a big issue because of the remote location of these supplies we are likely to have a lot of noise on them and for at least the Lock-In mode of operation the cutoff of the S-D Voltage Filter appears to be above 60 Hz. I do not understand how you actually operate the SET transistor, e.g. as compared to a normal N Channel FET. Specifically: - How is the Gate Voltage defined and applied ??? is there a Gate to Ground supply or a Gate to Source supply ??? - Do you need to keep the SET's Source fixed with respect to Ground as the current through the SET changes ??? in which case we can NOT RC filter the Source side of the SET's Bias supply but can only try to "AC clamp" it to Ground with capacitors. How to best run cables to the SET Bias Supplies ??? Because the output of both the SET Bias Voltage and Offset supplies needs to float the correct cabling is probably shielded twisted pairs, i.e. not coax. How to make best use of the Guard in the SET Bias Supplies ??? It looks like the Guard in these Yokogawa supplies is designed to be a noise current Guard not just a DC leakage type of Guard so if used correctly this Guard could help a lot to control noise in your application. I currently understand that the SET Bias Offset is bipolar and is thought to span the range from -3V to +3V. ??? 4. Signal Filter Box: Design of the Signal Filters, i.e. 4 pole at 1 Hz for DVM operation and at 100 Hz for the Lock-In operation looks OK and rational. In Bessel this looks doable with a limited range of reasonable value capacitors and resistors. The current Signal Filter design has a gain of 10 for each 4 pole filter. The in cryostat Instrumentation Amplifiers will run with a gain of 100 or 200 so the overall system gain will be 1000 or 2000. All critical capacitors in the Signal Filter Box are reasonable value Polypropylene, +- 5%, -200 ppm/deg C (other critical signal filter capacitor characteristics are listed in another document). Capacitors from this same type family and value are used in the final stage of the SET Bias Filters. All resistors in the Signal Filter Box are of reasonable value and are standard 1% 100 ppm/deg C. We can use fancier resistors for the cold Instrumentation Amps and for the cold SET Bias Voltage divider. All of these resistors are easy to obtain. The current plan it to have the 100 Hz and 1 Hz filters in parallel. If the two filters were put in series (100 Hz first) then we should include a buffer on the output of the 100 Hz Filter. If the filters were put in series can we stand the gain of 100 ??? or do we need to attenuate between the series filters ??? The intent is to include components for all options on the Signal Filter pcb. The Signal Filter design uses one pcb for a total of 8 poles of filtering for SET Voltage signal and a separate identical pcb for a total of 8 poles of filtering for the SET Current Signal. Each Signal Filter pcb also holds a fully isolated power supply for the opamps and that pcb. This is a fancy low noise isolated power supply and just the cut off power section of this Signal Filter pcb is used for the Instrument Amplifier power supply in the Power/Bias Filter Box. Each Signal Filter pcb will need separate Ground connections to the Cryostat Ground Point for: its input, its output, and its power supplies - about 4 ground connections to the cryostat. Would a Signal Filter design with a fully passive input stage improve the design (is it necessary) ??? The issue of concern here is the peak amplitude of the noise at the input of the Signal Filter. Very approximate size of the Signal Filter Box: 9" x 5" x 4". The Signal Filter Box needs to be mechanically mounted within a few feet of the Inst Amp Power Supply & SET Bias Filter Box. It's mechanical mount must also provide a stiff electrical connection to the heavy cryostat top plate. Signal Filter Box Connectors, Controls, and Indicators: Input connector, 4 BNC Output connectors, Power input connector, No Controls, Power On LEDs. 5. Isolated Power Source Box: This box uses normal AC wall outlet line power and provides up to 20 Watts of stable isolated 25 kHz sin wave output power at about 25 Vpp. This box provides 3 isolated outputs. This box can be located remotely (up to 20 feet) from the rest of the SET Curve Tracer electronics. This box needs a ground connection to the large cryostat head plate. This Power Source Box has the following controls and indicators: Line Power On/Off, Stand-By/Operate, Line Power On LED, Over Load LED, Output Power On LED. The size of the isolated power box should be about 1/2 cubic foot. See the file dans_notes_set_curve_tracer.txt for additional questions, points, and descriptions about the Set DC Curve Tracer.