[sdiy] expo accuracy? or integrator accuracy?, or both?

[Scott Bernardi]

I'll comment on one of these error components - input bias current. The input bias
current of a JFET type opamp (TL7x) comes from the leakage of a reverse biased pn
junction, and that tends to double every 10 degrees C or so.  The CMOS input types
(CA3140 et al) do not suffer from this, and so are generally chosen for VCO
integrators.


>
> >-amplifier input bias current (easy to understand,
> >  steals current, will get worse with temperature,
> >  leads to shift of some Hz down, parts with less then
> >  30pA are expensive and sometimes slow)
>
> Yes, increases with temperature are quite dramatic. Watch for specs given
> at just room temperature vs. those given over a range when comparing
> integrators.
>