Preamps (PRE) and Sensors

Rachel HochmanJohn Bonnell

Space Sciences LaboratoryUniversity of California, Berkeley

CDR September 30-October1, 2009

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Overview

• Motivations and Driving Requirements• Sensors and Enclosures • Resources: Mass, Power• Schematics• Frequency Response: modeling, bench testing, fully-assembled• PWB Layout  and Fabrication• Parts Derating and Stress Analysis• Radiation Effects Testing: TID and DDD• ETU Thermal Qualification • Test Plan and Flight Test Procedures• Backup Slides

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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.• The non-linear coupling (I-V curve) of EFW sensors to the external E-field can be optimized

through current biasing (factor of 100 decrease in susceptibility to systematic error sources and density fluctuations).

• This 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).

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Board Requirements/Specs

• Driving Environmental Requirements– Radiation (TID and Deep Dielectric Discharge)– Temperature (sunlit to eclipse swings)

• Driving Measurement Requirements– 0.3-mV/m accuracy at DC in the spin plane (EFW-49).– 0.4-mV/m accuracy at DC on the spin axis (EFW-52).– 400-mV/m signals in the kHz band (large-amplitude EM fluctuations).– 400-kHz bandwidth with low noise floor (EMFISIS interface).

Reference numbers from: RBSP_EFW_SYS_001H_Requirements.xls

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EFW – Preamp

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SPB Preamp Sensors and Enclosures

• SPB enclosure directly derived from THEMIS-EFI (20 units on-orbit 19 months); minor modifications to accommodate DDD-mitigation caps.

fine wireushersurface

guardsurfaceSPB

cable

OP-15and

rad shield

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AXB Preamp Sensors and Enclosures

• AXB enclosure is AXB sensor (spherical shell).

• Includes 7-mm Al equivalent 4π radiation shields around OP-15.

Sphere

Whip (Stub or Usher)

Hinge (Guard)

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The Preamps Themselves

• Each SPB PRE as shown weighs 3 g, with a 10-g Tantalum cover (13 g total).

• Each AXB PRE assembly masses 13 g.

• POWER Consumption: each preamp draws 3 mA of current per supply (+/-15V) within expected range of inputs/ operational environmental limits.

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Schematic (SPB)

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Schematic (AXB)

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• Sheath impedance is Rs || Cs, and connects to SPHERE.• Output load is Cc || (Rc + RL), connected to Vout.

EFW – Preamp Response Model

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• Faraday Box can be Grounded or Driven by Signal Generator.• Measuring AC gain in both configurations allows for estimation of Cstray and Ci.

EFW – Preamp Measuring Input Impedance

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SPB

PRE

StrayCapacitance –

Sphere and Fine WireTo Box

Signal Gen

Bench Testing

AXB PRE Gain v Freq Driven Box

0

0.2

0.4

0.6

0.8

1

1.2

0.1 1 10 100 1000 10000 100000 1000000 10000000

Frequency (Hz)

Gai

n

AXB PRE Phase v Freq Driven Box

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

0.1 1 10 100 1000 10000 100000 1000000 10000000

Frequency (Hz)

Pha

se (D

eg)

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P 2

S P R I N G C O N TA C T

C 4 1 . 0 n F

C D R 3 1 B X1 0 2 B K U S

1 0 0 V

Plasma Simulator+1 5 V

-V

+

-

U 1

O P 1 5O P -1 5 A J / 8 8 3 B

3

26

7 14 5

8

Cleared of Ground Plane

Usher

+ V

R 2 1 0 0M 5 5 3 4 2 E 0 6 B 1 0 0 D R

R 1 1 0 0 kM 5 5 3 4 2 E 0 6 B 1 0 0 E R

B ias

R 3 7 5 MS 1 2 0 6 C P X7 5 6 J

Usher Ring(B ottomS ide)

Vout measured here

-1 5 V

C 3 1 . 0 n FC D R 3 1 B X1 0 2 B K U S

1 0 0 V

Guard Ring(TO-99s ide)

Ground Plane

Signal In

S hield

C 2 1 0 p FC D R 3 1 B P 1 0 0 B K U S

Guard

R 4 1 kM 5 5 3 4 2 E 0 6 B 1 E 0 0 R

+ C 1 AC W R 0 6 -0 . 1 u F

5 0 VC W R 0 6 N H 1 0 4 K B B

C p s

1 0 p F

C 5

4 . 7 n F

V out

Radiation Shield, connects to -V pin and OP15 pin 4 via pads on board

R p s

8 0 M

+ C 1 BC W R 0 6 -0 . 1 u F

5 0 VC W R 0 6 N H 1 0 4 K B B

• Little difference in AC gain between Grounded and Driven configurations.

• Stray capacitance small.• AC Gain ≈ Cs/(Cs+Ci) →• Ci ≈ Cs*(1/Gv -1) ≈ 5 pF

ETU PRE and Cable Response

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• Sphere and partially-deployed Fine Wire in F-Box, with ETU SPB.

• Plasma Sim is 80-MΩ ║ 10-pF (worst case magnetospheric).

• Grounded AC Gain ≈ 0.7.• Driven AC Gain ≈ 0.4.• Ci ≈ 7.5 pF, Cstray ≈ 7.5 pF.

• Increasing plasma density:• Moves knee to higher

frequency (Rs decreases).• Moves AC gain closer to 1

(increases Cs as Debye length approaches dimension of sensor).

Parameter Description SPB AXB

Rs [Mohm] Sheath resistance 50

Cs [pF] Sheath capacitance 14 4

Re [kohm] ESD protection – resistor 100

Ce [pF] ESD protection – bypass capacitor

10

Ri [Tohm] Follower -- input resistance

1

Ci [pF] Follower – input capacitance

7.5

Ro [ohm] Output resistor 100

Lc [m] Cable length 48 7

dC/dL [pF/m] Cable cap/length 100

dR/dL [ohm/m] Cable resistance/length 1.5

RL [kohm] Load resistance 100

EFW – Preamp Predicted Frequency Response

• Worst case Magnetospheric response, based on measured ETU input impedance (Aug 2009).

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Layout (SPB)

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Layout (AXB)

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Board Fabrication

• The boards are made of Arlon 85NT, which is a polyimide resin on Thermount (non-woven aramid) to minimize differential CTE over broad temperature ranges experienced by the preamp PWBs:– -135 C to + 90 C; THEMIS-EFI experience.– -150 C to +70 C; RBSP-EFW CBE.

• Thermount is hygroscopic, therefore extra care must be exercised in handling and storing to avoid moisture absorption, and the boards must be baked out prior to mounting parts. Assembly instructions covering this already in-place.

• Coupons for both SPB and AXB PWBs are in-house, and will be sent out for testing in Q3 2009, according to schedule.

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Derating

• All preamp components meet the voltage and stress derating guidelines set forth in EEE-INST-002.pdf

• Temperature range effects taken into consideration.• Complete table with values in backup slides.

Radiation (TID) Testing

• As per an I-PDR RFA (REF#), a TID test of the flight lot and date code of OP-15 was performed.

• At 100-kRad(Si) TID, the only relevant parametric change was in VOS, which rose to as high as 32 mV, but was stable.

• EFW ConOps includes on-the-fly removal of differential offset voltage effects, so this magnitude of VOS (equiv. to up to .4 mV/m on 80-m antenna) can be tolerated, and still achieve measurement requirements.

• Test Report: ftp://apollo.ssl.berkeley.edu/pub/RBSP/1.2. Systems/3. Test/RBSP_EFW_TR_005_OP15TIDTest.doc

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Deep Dielectric Discharge Mitigation

• The preamp enclosure does not provide 350-mil Al equivalent shielding for the preamp components, so evaluation of DDD susceptibility required.

• The OP-15 op amp was tested for susceptibility to damage by DDD using the test defined in the RBSP EMECP.

• Only pins found to be susceptible at the 1500-V test level were the COMP inputs.

• Mitigation capacitors were added between the COMP inputs and FGND, and were found to have no significant impact on frequency response.

• One N/C pin was also connected to FGND to implement the “no floating conductors allowed” requirement.

• Complete test report available on RBSP-EFW FTP site: ftp://apollo.ssl.berkeley.edu/pub/RBSP/1.2. Systems/3. Test/RBSP_EFW_PRE_TR_001A_OP15DDDTest.doc

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ETU Thermal Qualification

• One survival cycle, two operational cycles.• Survival cycle from -170 to +90 (powered off).• Operational requirements are -160 to 80. With and additional 10

degrees at each extreme, the operational cycle tests were run at -170 and +90 (powered on). Power cycle tests performed at extreme high and low limits.

• Cold limit is met in eclipse, and EFW not required to make measurements in eclipse, and so units must survive cold, but need not stay in spec.

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Temperature profile for operational cycles

Load Preamp

PWB

Integrate Preamp PWB and Sphere to

Cable

Test Preamp PWB.

Bench and Thermal.

Integrate Cable Assembly to SPB Chassis

Stow Cable

Adjust limits and

setpoints

Electrical Functional

Test

Functional Deploy/ Length

Calibration

Stow Cable

Electrical Functional

Test

Vibration Test

Electrical Functional

Test

Hot TVAC Deploy

Stow Cable

Stow Cable

Cold TVAC Deploy

Electrical Functional

Test

Electrical Functional

Test

Deliver to Science

Cal

PER

Test Flow (example of PRE→SPB)

Test Procedure for Flight

• THEMIS procedures used with slight modifications; for example:– preamp supply is now at +/- 15V rather than +/- 10V.– Large amplitude input tests in addition to lower amplitude frequency

response. • New documents:

– RBSP_EFW_PRE_BenchTest_Proc.xls for board level checkout, – RBSP_EFW_PRE_TVAC_Proc.xls for thermal vacuum testing.

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BACKUP SLIDES

Grounding

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

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Part Type Part Numbers Rating Derating Percentage

(voltage, power) at 90C

Expected V, Power

CWR C1A, C1B 50V 40%, n/a(50% at 70C)

15 V

CDR C2, C3, C4 100V 60%, n/a < 15 V

RM R1, R2, R4 50V, 50mW 46%, 35%(80%, 60% at 70C)

R1 <15V,2mWR2 <1V,10mWR4 <1V, 1mW

RM R3 100V, 250mW 46%, 35%(80%, 60% at 70C)

40 V, .02mW

Derating and Stress (Ref. EEE-INST-002)

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Parts List (AXB)

Item Qty Reference Value Part Number type tol rating mfg

1 2 C1B,C1A CWR06-0.1uF CWR06NH104KBB CWR06 10% 50V Vishay

2 1 C2 10pF CDR31BP100BKUS CDR31 10% 100V KMET

3 2 C3,C4 1.0nF CDR31BX102BKUS CDR31 10% 100V KMET

4 1 R1 100k M55342E06B100ER RM0705 1% 50V SOTA

5 1 R2 100 M55342E06B100DR RM0705 1% 50V SOTA

6 1 R3 75M H1206CPX756J RM1206 5% 100V SOTA

7 1 R4 1k M55342E06B1E00R RM0705 1% 50V SOTA

8 1 U1 OP15 AJ/883B OP15 AJ/883B TO-99     ADI

9 1 Teflon Tubing 8 x .15 in J-3643 JT&T       JT&T

10 1 OpAmp Base Shield UCB Custom Part RBSP-AXB-MEC-274       Davis MFG

11 1 Gore Cable <2.5 in RCN8818       Gore

12 1 PWB RBSP_EFW_PRE_002 RevB RBSP_EFW_PRE_002 RevB PWB     Valley Circuits

13 1 OpAmp Can Shield UCB Custom Part RBSP-AXB-MEC-273       UCB

14 1 Connector MCP12SS A22005-001       Omnetics

15 1 Preamp Post UCB Custom Part RBSP-AXB-MEC-262       UCB

16 1 Preamp Post Nut UCB Custom Part RBSP-AXB-MEC-266       UCB

17 1 Shield Clamp UCB Custom Part RBSP-AXB-MEC-275       UCB

18 2 Shield Clamp Post UCB Custom Part RBSP-AXB-MEC-276       UCB

19 4 SHCS #0-80 x 3/16" from ME Stores        

20 4 Flat Washer #0 from ME Stores        

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Parts List (SPB)

Item Qty Reference Value Part Number type tol rating mfg

1 7 Vout,Sheild,Bias,-V,+V, Usher, Guard 0.025 Printed Circuit Pin 3114-2-00-34-00-00-08-0 PIN     MILL_MAX

2 2 C1B,C1A CWR06-0.1 uF, A_Case CWR06NH104KBB CWR06 10% 50V Vishay

3 1 C2 10pF CDR31BP100BKUS CDR31 10% 100V KMET

4 2 C3,C4 1.0nF CDR31BX102BKUS CDR31 10% 100V KMET

5 1 R1 100k M55342E06B100ER RM0705 1% 50V SOTA

6 1 R2 100 M55342E06B100DR RM0705 1% 50V SOTA

7 1 R3 75M H1206CPX756J RM1206 5% 100V SOTA

8 1 R4 1k M55342E06B1E00R RM0705 1% 50V SOTA

9 1 U1 OP15 AJ/883B OP15 AJ/883B TO-99     ADI

10 1 Teflon Tubing 22 GA, Wall Thickness .010 J-3643 JT&T       JT&T

11 1 Front Shield UCB Custom Part RBSP-SPB-MEC-809       Davis MFG

12 1 Can Shield UCB Custom Part RBSP-SPB-MEC-810       Davis MFG

13 1 Spring UCB Custom Part RBSP-SPB-MEC-812       Davis MFG

14 1 PWB SPB PREAMP PWA RBSP_EFW_PRE_001 RevA PWA     Valley Circuits

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