FW: Quadrature VCO Module finished

[Haible_Juergen#Tel2743]

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From: Haible_Juergen#Tel2743
To: till
Subject: Re: Quadrature VCO Module finished
Date: Monday, 11. September 1995 08:58


   (as described in Tietze/Schenk, Halbleiterschaltungstechnik).

How does this quadrature part of the circuit work?  Is the OTA
functioning as a second integrator?

Yes. And to avoid the second integrator to run to its rails,
there is a second feedback loop, i. e. the output of the
2nd integrator is fed back to the first comparator with a
rather large resistor. Tietze/Schenk show, that as soon as
the offset adjustment is done, the second feedback path
will not affect the switching time of the first comparator anymore.
But if there is some offset drift, the triangle symmetry is
slightly changed, until the offset is zero again. Very nice
circuit, IMO!

JH.