[sdiy] fast opamp with low offset

[Ingo Debus]

Am 03.04.2010 um 19:46 schrieb David G. Dixon:

> In my experience, the 2164 puts out a very precise current.  To  
> then convert
> this to a voltage and back with an opamp, even a precision one,  
> seems like a
> real step backward.
>
> In the meantime, simulations suggest that all I have to do is put a  
> passive
> LPF on the 2164 current output to filter the spikes to well within the
> compliance range.  This would be a very convenient fix, since it  
> only adds
> one resistor and one cap to the circuit.  Of course, with this  
> method, one
> has to use a very small resistor so as not to create a voltage  
> outside of
> the +/-0.1V compliance range at the 2164 output.

Haven't followed too closely, so this perhaps isn't helpful, but  
nevertheless:
If you want a current-input current-output RC lowpass, you have to  
put our well-known voltage-input voltage-output RC lowpass backwards:  
the resistor still goes from input to output, but the cap to ground  
is on the input side. Think of it as a current divider rather than a  
voltage divider. Part of the current (the higher frequencies) goes  
directly to ground via the cap, the other part of the current goes  
via the resistor into the (low input impedance) current sink.

Ingo