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ADA4817 low frequency (10 Hz) voltage (&current) noise, alternatives

Question asked by Qutechie on Oct 6, 2015
Latest reply on Oct 16, 2015 by rvieja

Dear ladies and gentlemen,

in our project on silicon quantum computation we require ultra low
noise operational amplifiers to measure current changes of pA on nA
Signals. (Thus input impedances of order 10^12 ohm)

I checked your website and found the ADA4817 with nV/sqrt(Hz) voltage
noise and pA/sqrt(Hz) current noise. Our sample resistance of
25-100kOhm necessitates 1-100 fA/sqrt(Hz) and 1-50 nV/sqrt(Hz).

We have 2 I/V converter applications in mind:

1. "fast&high IV gain measurements"(1-10 kHz range) - for pulses and
Voltage noise insensitive measurements high ohmic feedback Resistor
(1-100GOhm) current noise corner frequency <1-10 Hz voltage noise cf
<1-10kHz gain bandwidth product (Gain 1) >100MHz-1GHz

2."slow&medium IV gain measurements"(1mHz- 1kHz) - for small signals,
long averaging and voltage noise sensitive measurements medium ohmic
feedback resistor (100MOhm-1GOhm) current&voltage noise corner
frequency <10Hz (voltage corner if possible <1Hz) gain 1 bandwidth

The noise level was specified @100kHz. How high are these levels below? Is the
ADA4817 fit for any of the cases or can you recommend an alternative?

Further “nice to have” specs are a TO99 8pin packaging factor, possibility of
+/-15V source operation and an pin for external offset compensation.

Thank you for your help.