Variable ramp again

[harry bissell]

I tried simulating this in EWB and it does work... but I get amplitude wariation with
duty cycle as well as with frequency. I tried some feedback to solve the integrator
inaccuracy and it works... but it responds like a PLL (under/overdamped etc) and that
isn't good news. Maybe a synchronous scheme (S/H?) would remove this effect. Keep me in
the thread....

:^) Harry Bissell

mbartkow at ET.PUT.Poznan.PL wrote:

> Oh, my fault I didn't explain how it works.
> It's very simple, though. Consider a nonsymmetrical pulse wave, e.g with PW=10%.
> Removing the DC offset means that a constant value is added which causes that
> the areas under the negative "half" and the positive "half" are equal. In other
> words, the integral of the wave calculated over whole period is zero. In our case,
> the negative part should have 1/9 of the amplitude of the positive part. These
> different amplitudes cause different slopes of the ramp observed at the integrator
> output. Since ideally the pulse wave has zero DC, the integrator should not drift.
> As this is not achievable (for example, the comparator output levels may not be
> strictly symmetrical) a correcting feedback is needed (thanks JH for the interesting
> point here)
>
> MB
> (I am in Hannover for two weeks, and replying remotely)