Precision DC amplifier II?

[Valejan]

In an effort to construct a highly accurate DC amplifier ,amplifiers have found a solution that can gain up to 10.000x
ie 1.000 mV amplifes on 10.0000V, 10nV on 100uV. Amplifier work in measurement system with accuracy 0,5ppm. Construction is about 20 years old.
Honestly, construction has taken me so that I copied it.
Unfortunately, the input amplifier is designed from discrete components (JFET input pair).
Do you think that today was to find an amplifier that could replace the imput amp?
What should OPA140 ?

 

[jiripolivka]

You can try one of precision opamps available. For the first stage I would recommend using a chopper-type opamp. AD, TI and others offer several good ones. I used a chopper opamp in G=10 000 application, without drift and distortion.

 

[Valejan]

I'm not sure. Chopper-type opamp have higger Noise and unbalanced current to the input (toothy)-.
I need minim Power supply +-5V for example AD8638 have noise 66nV/Sqrt(Hz).

 

[rmorris]

No time to look up specs atm but I'd start with OPA177 (Texas). Chopper amps can have some issues as noted above but maybe worth a look at latest devices.