[sdiy] integrator / capacitor leakage

[ASSI]

On Dienstag, 6. Dezember 2005 21:21, René Schmitz wrote:
> The ones I have played with (AD9852, AD9835) worked down to audio
> frequencies, and there is no reason why they shouldn't work down to
> the minimal programmable frequency if the output circuitry is DC
> coupled. There are some that have a direct quadrature output, which
> would be handy.

The problem is not the low output frequency itself, but the low 
resolution in both the amplitude and time domain at such frequencies. I 
would expect that the resulting spurs wouldn't work all too well for a 
frequency shifter.

I think something like the Silicon Labs 8051F120 (reasonably priced 
boards at www.elmicro.com or the german alter ego 
www.elektronikladen.de :-) would be well worth the trouble of some 
programming - however Jürgen said "no programming", which kind of puts 
these off limits.

Coming back to an analog implementation (I have to say I haven't fully 
thought this through), maybe one could use a synthetic inductor (via an 
impedance converter, implemented with an OTA to make it voltage 
controllable) for the resonant tank. For a suitable oscillator topology 
one could then tap off both the voltage over and the "current" through 
the synthetic inductor as voltages - and these should be in quadrature.


Achim.
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