Op-amp question

[col_implant]

Maybe this is a silly question....

Is it possible to apply a level shift to a transimpeedance amplifier? I searched google and only got patents as results... this tells me no!

 

[jeg223]

you can pull the input signal up to whatever level you want. It works like a linear combination circuit. If you use a voltage source make sure the input resistor is equal to the feedback resistor so your offset gain is unity.

 

[col_implant]

I was thinking of using a PIC Comparator reference voltage, output directly to V+ input.

The currents I'm measuring are quite small (100pA min). Could noise on the reference be a problem? Perhapps decoupling required?

 

[jeg223]

Don't you have to worry about the input bias currents at that point?

 

[col_implant]

Wel input bias is of the order of 1pA, quite a good amp we are using

 

[jeg223]

In that case, Vout= V+ - Rf* Iin
Although bias current and offset voltage may make life miserable.