Does anyone ever buffer instrumentation amps?

[q2418130103p]

Instrumentation amps with low bias (pA) usually have higher noise (>10nV/rHz).

Does anyone ever buffer a low noise (<10nV/rHz) instrumentation amp, which probably has nA bias, with low noise low bias op amps?

Are there any other ways to mitigate the noise contribution of low bias instrumentation amps?

Thanks

 

[FvM]

You find low noise FET OPs down to about 3 nV/√Hz noise density. Using it in a differential input stage with gain will result in about 4.5 nV/√Hz input referred noise. Lower noise at the cost of higher offset voltages and drift can be achieved with discrete JFET input stages.

 

[q2418130103p]

I am not sure I know what you mean by 'discrete jfet input stages'. Could you elaborate, or provide a reference?

 

[FvM]

Discrete means using individual JFET transistors instead of IC. I just wanted to mention the option, not suggest a complete design solution.