[sdiy] integrator / capacitor leakage

[JH.]

> I think the answer is so obvious, it is hard to see.
> Any multiplication (amplification) of the integrator output will
> multiply the errors by the same factor.
>
> So, commutative axiom says:
>
> (Signal + Error) * 10 = (10 * Signal) + (10 * Error)

That's the first order approximation. But Error might be a function
Error(Signal).


> For 20 kHz top end you will need to slew 20 volts in 50 microseconds.
> That is 0.4 volts per microsecond. Not demanding by todays standards.

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.

JH.



>
>
> On Dec 3, 2005, at 6:47 AM, JH. wrote:
>
> > Thanks for the opamp hint.
> >
> > But for a given set of parts (opamps, caps, etc.), would
> > running the VCO at lower level, and then amplifying, have
> > any advantage or rather not?
> >
> > JH.
> >
> >
> > ----- Original Message -----
> > From: "Grant Richter" <grichter at asapnet.net>
> > To: "Synth DIY" <synth-diy at dropmix.xs4all.nl>
> > Sent: Saturday, December 03, 2005 6:44 AM
> > Subject: Re: [sdiy] integrator / capacitor leakage
> >
> >
> >>>
> >>>
> >>> Good amplifiers are easier to find.
> >>>
> >>
> >> Burr Brown used to make an amplifier in the pico-amp input bias
> >> range. OPA404 (EOL I bet)
> >>
> >> http://www.compel.ru/pdf/TI_BB/OPA404.pdf
> >>
> >> They recommended cleaning the chip with IPA to get finger oils off.
> >> Contamination from handling chip was enough to throw integrator TC
> >> off.
> >>
> >>
>
>