Peer Review September 3, 2009

1. Peer Review September 3, 2009 Preamps (PRE) Rachel Hochman John Bonnell Space Sciences Laboratory University of California, Berkeley

2. Overview • Overview of circuit • Board requirements / specification • Schematic - can be on ppt, or from Orcad • Layout - can be on ppt or gerbers or layout program • Board Fabrication - material, standard, • Derating - show we meet INST_EE_0022 • Radiation - radiation testing (TID and SEE) on parts done by us, or procurement of rad hard / rad tolerant parts • DDD - results from DDD testing where applicable. • Grounding - board grounding scheme • Thermal - board thermal analysis for components drawing more than 100mW • Mass - mass of board, mass of 'heavy' components, staking plan • Power - average and peak • Parts List / Issues • Functional Testing done on ETU and any still to do • Test plan and procedure for flight unit

3. Motivation (In Words) • The EFW Sensors, Preamp, BEB and EFW-EMFISIS interface represent the primary analog signal path for E-field measurements on RBSP. • Measuring 0.1 mV/m DC E-fields required accuracies of 0.1% in the magnetosphere: • tens of mV of signal in the presence of tens to hundreds of mV/m of effective common-mode or systematic noise (photocurrents, SC charging), or tens of volts of common mode signal. • Non-linear coupling (I-V curve) of EFW sensors to E-field can be optimized through current biasing (factor of 100 decrease in susceptibility to systematic error sources and density fluctuations). • Current biasing of sensors drives volts to tens of volts floating potential differences between sensors and SC ground. • High effective source impedance (plasma sheath, ten of MΩ), and low-noise and low-leakage current requirements (systematic error reduction again) drive use of low-voltage preamps in floating ground configuration. • Deflection and collection of stray photoelectron currents prior to impingement upon sensor also reduces DC biases (WHIP/USHER and GUARD surfaces).

4. Board Requirements/Specs • 2 Environmental Requirements • Radiation • Temperature • 2 measurement Requirements • Accuracy at dc • Large amplitude signals in kHz band

5. Schematic (SPB)

6. Schematic (AXB)

7. Layout (AXB)

8. Layout (SPB)

9. Board Fabrication • The boards are made of Arlon 85NT, which is a polyimide resin on Thermount (non-woven aramid). The material is hygroscopic, therefore extra care must be exercised in handling and storing to avoid moisture absorption. The boarsds must be baked out prior to mounting parts. For details see: Thermount_storage_drying_assembly_inst_REVA.pdf • Have coupons from the board house, but have not yet sent them to APL for testing

10. Derating • Must show that meets the specs on EEE-INST-0022: • CWR (C1A & C1B) must be operating at 50% of rated voltage… They are rated at 50V and only expected to see 15V, so that is acceptable. • CDR (C2-C4) at 60%... They are rated to 100V and only expect to see • Resistors are all RM type resistors, must be under 80% of voltage rating and 60% of power. R1, R2, R4 are all rated for 50V. R3 is rated for 100V • Power rating: R1, R2, and R4 are rated to 50 mW, R3 is rated to 250mW. • Reference document: EEE-INST-0022.pdf

11. Radiation Testing • Dave Curtis performed a Total Ionizing Dose radiation test and he found that to use these parts at 100krads one must tolerate VOS as high as 32mV, CMRR as high as -69dB, and PSRR as high as 256uV/V. • See test report by Dave Curtis at: ftp://apollo.ssl.berkeley.edu/pub/RBSP/1.2. Systems/3. Test/RBSP_EFW_TR_005_OP15TIDTest.doc

12. DDD • We shield the op15 but not all the insulators, so had to test that leads on op15 could survive DDD • Can’t protect input pins w/o compromising science measurement, but testing on unit F1 indicates the input pins are not susceptible to DDD damage at +/-1500V • Only susceptible pins were COMP inputs: • Addition of DDD-mitigation caps from COMP inputs to FGND. • Connection of N/C pin to FGND (no floating conductors allowed). • See the test report by Dave Curtis at: ftp://apollo.ssl.berkeley.edu/pub/RBSP/1.2. Systems/3. Test/RBSP_EFW_PRE_TR_001A_OP15DDDTest.doc

13. Grounding • the ground on the board is the floating ground from the LVPS and comes into the board on the shield pin.

14. Thermal • survival cycle from -170 to +90 (powered off). • operational cycle with turn-on tests at -160 and +90 (powered on) • Since EFW measurements are no good at low temperatures anyway, must simply survive in the cold regions • No parts draw more than 100mW

15. Mass/Staking Plan • Each SPB PRE as shown weighs 3 g • Each AXB PRE weighs 13 g • Staking: the wires inside the Gore cable on the AXB preamps is very delicate. Thus far we have been staking it as shown, but they have broken many times… AXB Mechanical Engineer Jeremy McCauley, John Bonnell, and myself are currently looking at new ways to provide strain relief to the wires.

16. Power Avg/Peak • The average current drawn by the preamps should not exceed 5mA per supply. For the 15V supply, this means the power consumption should be under 75mW • The current did exceed this limit, but only in extreme cold in thermal vacuum, and afterwards remained normal at operational temperatures.

17. Parts List (SPB)

18. Parts List (AXB)

19. Functional Testing Done

20. Testing Continued

21. Test Procedure for Flight • THEMIS procedures used with slight modifications, e.g. preamp supply is now at +/- 15V rather than +/- 10V. • New documents: RBSP_EFW_PRE_Test_Proc.xls for board level checkout