1. SPP FIELDS Preamplifier
Peer Review 24OCT2013

2. SPP FIELDS Instruments
Digital FIELDS Board (DFB)
DC to 64kHz (LF)
20nV/√Hz noise floor, 120Vpp max signals
Time Domain Sampler (TDS)
3kHz to 1MHz (MF)
20nV/√Hz noise floor, 20Vpp max signals
Radio Frequency Spectrometer (RFS)
30kHz to 20MHz (HF)
3-4nV/√Hz noise floor, 4Vpp max signals

3. SPP FIELDS Preamplifier

4. SPP FIELDS Preamplifier Concept - V1-V4

5. SPP FIELDS Preamplifier Concept – V5

6. SPP FIELDS Preamplifier Requirements
Input
RTI = antenna whip connector on preamp
Input impedance
> 1E+9 Ohms
Input current
< 2E-8 Amps
Input capacitance
< 40pF
LF output
Noise RTI
< 1uV/√Hz above 100Hz
Max input amplitude WRT FGND
20Vpp
+/-20V -3dB bandwidth
> 64kHz
Gain
1 +/-0.01%, DC to 300Hz 1 +/- 0.1%, above 300Hz
Output resistance
249 Ohms +/-0.1%, 100ppm/C

7. SPP FIELDS Preamplifier Requirements
MF output
Noise RTI
< 30nV/√Hz above 1kHz
Max input amplitude WRT FGND
20Vpp
+/-20V -3dB bandwidth
> 200kHz
Small signal -3dB bandwidth
> 1MHz
Gain
1 +/- 1%
Output resistance
249 Ohms +/-5%
HF output
Noise RTI
< 10nV above 100kHz; <4nV above 1MHz
4Vpp output -3dB bandwidth
> 20MHz
Gain
2 < gain < 10
Output resistance
50 Ohms +/-5%

8. SPP FIELDS Preamplifier Environmental
Radiation:
70krad total dose inside 0.1” aluminum box
All parts are SQPL 100krad or better
except JFET LSK389
Thermal: 0.25AU to 9.5Rs
min surv
w/ htr
max surv
min ops
max ops
V1-V4
-125 ?W 75
-40 V5
-220 60
-180 5

12. BACKUP SLIDES

19. Original
Design

20. Testing

21. Input Capacitance Test
Measured 20pF and test box strays with meter
Measured HF gain at low and high frequencies
C in = (20pF/Hfgain)-20pF
Conclusions:
Find alternative clamp diodes (DPAD or 2N5547)
Consider eliminating? Evaluate risk
U404, 2N5547 Cin not much lower, have 40-60% higher noise and inadequate gain bandwidth
LSK389 HF gain = 20/( ) = 0.19
Galaxy will = 10% increase in 3nV amp noise above 1MHz
60pF C base mitigates effect of JFET C in
Results:
LSK389 = 50pF with LSK389 as clamp diodes (not shown)
LSK389 = 25pF without clamp diodes
U404 and 2N5547 = 12-15pF

22. Noise Test Setup

23. HF Noise, Original Design

24. LF Noise, Original Design

25. Signal Evaluation Test Setup - Original Design

26. Signal Evaluation Test Setup - Proposed Design

27. MF Frequency Response Vs. Simulations

28. MF Harmonics - Original Design

29. MF Harmonics - Proposed Design

30. MF Harmonics - Proposed Design, Improved

31. Preamp Design To Do List
Evaluate tradeoffs in changes to mitigate harmonics
Do complete transfer function measurements with amplitude and phase
Measure thermal drifts from -80 to +80
Choose overall values for high and low gains

32. SPP FIELDS Preamplifier: LF Bootstrap

33. SPP FIELDS Preamplifier: LF Biasing

34. SPP FIELDS Preamplifier: HF antenna coupling

35. SPP FIELDS Preamplifier - Signal Levels
0.25 AU (54 Rs):
R plasma ~ 1MΩ
C coupling = 20pF
Gain = >10kHz

36. SPP FIELDS Preamplifier - Signal Levels
R plasma ~ 10kΩ
C coupling = 20pF
Gain = >1MHz

37. SPP FIELDS Preamplifier - HF Signals
Assuming
20pF source capacitance
60pF input capacitance

38. SPP FIELDS Preamplifier Requirements
LF requirements
Comments
[a] Input impedance > 1E+11 Ohms;
100GΩ; PA can meet this, but it is inappropriate for SPP environment and should be changed to reflect AEB loop gain requirements and expected plasma impedances
[b] Input current < 2E-8 Amps;
20nA;Easily met; OP15 max = 110pA across temperature, LSK389 is
[c] Input capacitance < 5 pF;
Should be revised; was originally written for OP15 alone but FET and strays are 25pF; can change to 40pF but real limit requires antenna characterization
[d] 100 Hz < nV/√Hz;
From science requirements; OP15 is 20nV
[e] -3 dB frequency ~ 500 Hz;
Should be deleted; this is actually the AEB FGND driver spec
[f] -3dB small signal BW > 64 KHz;
Guaranteed by OP15 GBW and SR
[g] Max Input amplitude > 20 Vpp;
Should be revised to max =20Vpp WRT FGND
[h] Gain of 1;
Should probably state accuracy of 0.1%; not to be confused with AEB loop gain accuracy
[i] Output resistance < Ohms.
Should be revised based on AEB LF loop DC gain requirements and should include accuracy and tempco

39. SPP FIELDS Preamplifier Requirements
MF requirements
Comments
[a] Input impedance > 1E+9 Ohms;
Redundant; delete or separate into input and output requirements
[b] Input current < 2E-8 Amps;
[c] Input capacitance < 10 pF;
[d] 100kHz < 20 nV/√Hz;
OP15 = 1kHz
[e] -3 dB frequency > 3 KHz;
This is roll-on frequency and has not been decided; delete?
[f] -3dB small signal BW > 1MHz;
Guaranteed by OP15 GBW and SR
[g] Max Input amplitude > 6 Vpp;
Should be revised to reflect change to shared output from OP15 for LF+MF
[h] Gain of 1;
Should probably state accuracy
[i] Output resistance < 240 Ohms.
Revise to = 249 Ohms +/-5% or delete

40. SPP FIELDS Preamplifier Requirements
HF requirements
Comments
[a] Input impedance > 1E+9 Ohms;
Redundant; delete or separate into input and output requirements
[b] Input current < 2E-8 Amps;
[c] Input capacitance < 10 pF;
[d] 100 KHz < 4 nV/√Hz;
Revise to 100kHz and 1MHz and state that this is referred to FET gate
[e] -3 dB frequency > 30KHz;
This is roll-on frequency; state differently?
[f] -3dB small signal BW > 20 MHz;
Easily met with AD8001
[g] Max Input amplitude > 0.9 Vpp;
State that this is referred to FET gate
[h] Gain of 7;
To be revised depending on antenna characteristics; set min/max? delete?
[i] Output resistance < 50 Ohms.
Revise to "50 Ohms +/-5%"