[sdiy] integrator / capacitor leakage

[Ian Fritz]

At 11:17 AM 12/3/05, JH. wrote:

>No. But I want to get 20kHz from 1mA maximum (to keep tracking
>errors reasonable), and I want to get down to 1/30s without switching
>capacitor values. Even that is no problem.
>But I want high waveform precision over the whole frequency range.
>Doing it with two integrators and/or shaping sin + cos, the amplitude error
>should be better than 1%, the phase error should be better than
>1 deg, and offset should be less than 5mV.
>Now suddenly it *is* demanding.

Boy that *is* tough. If you try to use IC OTAs you will  have trouble with 
the change in offset with Iabc and with amplitude variation from phase 
shift errors.  My non-OTA tri oscillator has about +/-2 mV offset variation 
from 100 Hz to 20 kHz.  Below that -- pretty hard to measure.  You might be 
able to get good enough OTAs using the MAT's in a discrete design, or by 
selecting through a big batch of CA3280's.

What exactly do you mean by phase error -- just the deviation from perfect 
quadrature?

I hate to say it, but for that kind of range and precision I would be 
tempted to go d*g*t*l.  :-)

   Ian