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

[Ian Fritz]

Hi Scott --

Yes, and again a tip of the hat to Terry Michaels for understanding this 
and using the CMOS amp in his design.

OTOH the best modern FET amps beat the CA3140.  Consider the OPA602 which 
is speced at 20 pA of bias current over -25C to +85C (for the best grades), 
and with a slew rate of 35V/usec.

I'm not saying we necessarily want to use this good of a device, but it's 
there.

   Ian


At 07:05 AM 2/7/2003, Scott Bernardi wrote:
>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.