SPP FIELDS PreampPower

Requirements01DEC2012 D. Seitz

Noise + BW + Dynamic RangeNoise• DC to 10 kHz, TBD nV/√Hz• 10 kHz to 700 kHz, 10 nV/√Hz• 700 kHz to 3 MHz, 3 nV/√Hz

Bandwidth• LF: DC - 64kHz; SR ≥ 4V/µs• MF: 2kHz – 1MHz; SR ≥ 60V/µs• HF: 2kHz – 20MHz; SR ≥ 1200V/µs

Dynamic Range• ±10V at LF in, x1 Gain• ±10V at MF in, x1 Gain• ±1V at HF in, x10 Gain

Some General Principles• Lower Noise = Higher Power

• Higher BW = Higher Power

• Larger Voltage Swings = Higher Power

We sort of want Everything. What will it cost?

POWER

AD8001 150mW

AD844 225mW

OPA602 90mW

44mW

490mW

>1 W!!

FETs 60mW

Termination power Probably unrealistic – but

what is realistic?

AD8001 150mW

AD844 225mW

OPA602 90mW

44mW

490mW

0.525 WAC coupled terminations, ignored

Non-flat responseFreq? Ampl?

FETs 60mW

AD8001 150mW

AD8001 150mW

OPA602 90mW

44mW

490mW

0.45 WAC coupled terminations, ignored

MF ±5V

FETs 60mW

AD8001 50mW

AD8001 50mW

OPA602 90mW

44mW

490mW

0.21 WAC coupled terminations, ignored

All HF, MF ±15V ±5V

+5V

-5V

+5V

-5V

FETs 20mW

HF, MF PowerSome typical op amp choices

• AD844 current feedback op amp– 60MHz GBW; 20MHz FPBW @ 20Vpp into 100Ω; 1200V/µs– 2nV/√Hz @ 1kHz– 225mW @ ±15Vs; 75mW @±5Vs– 100 krads - needs shielding (300 krad req)

• AD8001 current feedback op amp– 880MHz GBW; 40MHz FPBW @ 3Vpp into 100Ω; 1200V/µs– 2nV/√Hz @ 10kHz– ±5Vs max, 50mW @±5V (150mW if derived from ±15V)– 100 krads - needs shielding (300 krad req)

Dynamic range is reduced 3x by running @±5V

±10Vout requires ±15V supplies, not ±12V

HF, MF Load Power• Need 100Ω loads for termination– Will cut amplitudes in half at receivers– 7Vrms^2/100 = 490mW– 2Vrms^2/100 = 40mW

• Use AC coupled termination?– At what frequency?– What amplitude/power dissipation?– Frequency response will not be flat

Some LF Choices• OP15/16 legacy op amp

– 6-8MHz GBW; 15-25V/µs – 10^12Ω Rin – 15nV/√Hz @ 1kHz – 120/210mW@ ±15Vs – 100 krads - needs shielding (300 krad req)

• OP27– 8MHz GBW; 2.8V/µs – 3x10^12 Rin – 3nV/√Hz @ 1kHz – 100mW @±15Vs – 100 krads - needs shielding (300 krad req)

• OPA602– 6.5MHz GBW; 35V/µs – 10^14 Rin – 12nV/√Hz @ 1kHz – 90mW @±15Vs – ??? krads – need to find out; used on Solar Orbiter

Total Power(assuming termination load mitigation somehow)

Best case:Run FETs, HF and MF @±5V using AD8001, DC coupled termAssume 100mW LF

• LF = 100mW• MF = 50mW• HF = 50mW• Loads = 90mW

Total: 290mW/preampX4.5 = 1.26W

Worst case:Run FETs, HF and MF @±15V using AD844, AC coupled term guessAssume 150mW LF

• LF = 150mW• MF = 225mW• HF = 225mW• Loads = 200mW

Total: 800mW/preampX4.5 = 3.4W

Total PowerOne possible compromise:Run FETs @±15V and ÷2 into MF, HF stages, DC coupled terminationsRun MF and HF at ±5V derived from ±15V using AD8001Assume 100mW LF

• LF = 100mW• MF = 150mW• HF = 150mW• Loads = 90mW

Total: 590mW/preampX4.5 = 2.46W

Price:• HF, MF dynamic range smaller• HF, MF noise RTI >>2nV/√Hz

HF, MF Power Supply Rails

SNR versus Vsupply:

• ±5Vs

– HF: 20MHz SNR (2Vrms/20nV/√Hz) = 85dB (300mVpp max Vin)

– MF: 1MHz SNR (2Vrms/2nV/√Hz) = 118dB (3Vpp max Vin)

• ±15Vs

– HF: 20MHz SNR (7Vrms/20nV/√Hz) = 96dB (2Vpp max Vin)

– MF: 1MHz SNR (7Vrms/2nV/√Hz) = 129dB (20Vpp max Vin)