1. Electrical System Nov. 15, 2010 Monte Frandsen

2. Key Electronics Design Goals and Constraints Minimal change between ground and airborne observations Signals pass through a vacuum bulkhead Signals (wires) transition between77K to ambient Electronics, (pre-amps), are subject to changing environmental conditions Packaging and connectors Vacuum bulkhead Size, placement, and number of wires Thermal effects Temperature gradients (wires) Ambient-operating point shifts etc 2

3. Primary Electronics Design Tasks Cryo-Cooler Electrical Integration Controller Power Supply Temperature Sensors LWIR Detector Interface MWIR Interface Connectors and Packaging 3

4. Cryo-Cooler Integration Cyro-cooler controller Primarily a packaging task Connectors and wiring Power Supply Connector Serial Port Connector Cold head temperature sensor connections Must be mounted within ??? from the cryo pump —(waiting on info from the manufacturer) 4

5. Cryo-Cooler Power Supply Boosts voltage to 48V to provide power to the Sunpower GT controller Requirements: Can be remotely mounting away from optical bench. Input Voltage 28VDC Expected Input power requirements ~30 Amp peak current draw (<10 seconds) ~15 Amps Max continuous Output Power 48VDC 15 Amps peak (< 10 Seconds) 300 Watts maximum continous load 5

6. Cryo-Cooler Power Supply Design Based on the Vicor Maxi Power Module Three modules paralleled to meet peak load and share the load current Schematic based on manufacturer’s reference design 6

7. Temperature Sensors RTD Cryo Cooler cold head. Supplied by manufacturer. Two leads directly interface to the cryo-controller. Two lead Cryo cooler heat sink temperature Lakeshore DT-670 Si Diodes Expected accuracy 0.1K around 77K Can be individually calibrated for higher accuracy as required. Trade off between operation range vs. sensitivity Locations (tbd) Jusdon 2N2222 Si Diode Part of the LWIR detector assembly Circuit expected the be the same as the DT-670 interface 7

8. Temperature Sensors LakeShore DT-670 Si Diode Sensors Standard temperature curve 4-wire measurement Minimize lead errors due to temperature shifts. May be able to use 2-lead system with reduced performance. 10µA Bias current 8

9. Temperature Sensor Interface 9 Low bandwidth-Low power Component Requirements Precision amplifiers and Precision Reference High stability Very low drift /temperature coefficients Vos and Gain. Resistors Vishay precision bulk foil with TC < 1 ppm.

10. LWIR Detector Signals Requirements 12 independent Channels Expected Sensor Bias Currents 10mA - 40mA (originally this was 1mA to 50mA) 0.5V to 3V DC bias voltage across the detectors 100 Ω typical detector impedance 1mV dynamic range. 10

11. LWIR Pre-Amp Circuit Design DC Servo Integrator feedback topology Proven on previous MAS sensor Integrator nulls DC-Errors. Also nulls any other DC sources within the limitations of the op-amp. Transfer function is a high pass filter with a very low cut- off frequency 11

12. LWIR Pre-Amp Circuit Design Advantages Supports 2-wire interface Nulls out ALL slow-time varying changes including Vos Lead –resistances shifts Bias voltage shifts Bias current shifts 12 Disadvantages Not an absolute metric (typically ratio-metric) No common mode rejection Practical limitations on the integrator will prevent the DC from being driven nulled to 0. (< 10mV typical) Input signal must be chopped (AC) In use and during calibration Scan – “droop” or background fading pushes out the low-frequency cut-off.

13. LWIR Pre-Amp Circuit Design 13 Simplified Circuit 1.Unity Gain 2.Gain~1000 3.Integrator 4.Difference Amplifier

14. Key Amplifier Requirements Amplifier 1. Unity Gain Ultra-Low Voltage Noise. Low 1/Fc-noise Unity Gain Stable Amplifier 2. High Gain (1000) Inverting Ultra-Low Voltage Noise. Low 1/Fc-noise GBW Product > 40MHz Max-Freq ~40Khz Amplifier 3. Integrator Ultra-Low Input Current Precision (Low Vos) Amplifier 4. Differential output preferred. High capacitive loading Short circuit protected 14

15. Preliminary Noise Estimates Noise Estimate summary Assumptions Temperature = 300K (~27°C) Detector modeled at 82 Ohms Op amp noise models typically change in the.1 to 10Hz range. Parameters are selected > 10Hz. @Amplifier 1 LT1128 en~ 5nV/sqrt(Hz) (@ 10Hz) @Amplifier 2 (LT1037) en~ 5nV/sqrt(Hz) (@ 10Hz) After Stage 2 gain of 1000 15

16. Preliminary Noise Estimates Noise Estimate summary (continued) With a 40kHz bandwidth, the expected mean noise output voltage ~Vm ≈ eout*sqrt(Bandwidth) Vm ≈ 1.7mV LT-Spice Noise Simulation shows ~12mV/Hz 1/2 - -Still need to reconcile the differences 16

17. Additional LWIR Error sources Low frequency op amp noise Op-Amp Power Supply PSSR (at 40Khz) 60dB @1mV ripple  1mV error Reference Voltage noise Primarily on the Bias voltage Common Mode tbd CrossTalk EMI/EMC pickup from cryo-pump Shield cables near the pump. 17

18. LWIR Output Full Scale output ± 5V Dynamic range from sensor Dependent on the detectors >± 1V Differential output op-amp with reasonable drive capabilities to drive twisted pair line. Nominal impedance 100Ω Based on previous reference design 50Ω on each wire. 18

19. MWIR Interface Currently do not have sensor specifications Cooled transimpedance pre-amp is part of the detector Expected interface Instrumentation amplifier Gain <100 Maximum Bandwidth 40Khz 4-wire interface Power Gnd Signal Signal-Gnd Output Interface similar to LWIR 19

20. Connectors and Wiring Pre-Amp Interface (External) Total signals --33 12 LWIR 12 MWIR (11 slots unused) 9 Temperature 6 cold 1 Hot cryo pump temperature 1 preamp Input Power +28V ~70 connections D38999 Series III connectors Insert: 21-35 (79 contacts #22). Plug PN: D38999/26WG35SN 20

21. Connectors and Wiring Pre-Amp to Vacuum Connectors Connections Wire count for 4-wire interface system (separate wires for bias and signals) Total signals --33 12 LWIR 12 MWIR (11 slots unused) 5 Temperature 2 LWIR 1 Cryo pump cold head 3 general 116 Connections (wire count) Vacuum Bulkhead Connectors 3-50 pin DSUB Bulkhead connectors PN# Preamp Connectors 3-Micro-D style (MIL-DTL-83513 Style ) Lead-times. Lead-times may force migrations to standard DSUB connectors 21

22. Connectors and Wiring Cryo Pump Power Supply and Cryo Controller. D38999 Series III connectors Inserts/Shells not yet finalized. 22