Quadrature VCO Module finished

[Don Tillman]

   Date: Fri, 08 Sep 1995 09:40:00 -0700 (PDT)
   From: Haible_Juergen

   For all those who are interested, I got my Quadrature VCO
   Module finished last night.

   It contains a sin / cos VCO, that is built around 2 LM13600's and
   some TL07x opamps. The core is a schmitt-trigger / integrator
   triangle generator. A second comparator / ota-integrator pair
   generates a second triangle wave with 90 degrees phase shift
   (as described in Tietze/Schenk, Halbleiterschaltungstechnik).

How does this quadrature part of the circuit work?  Is the OTA
functioning as a second integrator?  If so, how do you avoid dc offset
drift?  Or is the OTA functioning to invert the main triangle every
other quadrant and add the schmitt square wave as an offset?  If so,
is there any deglitching?  Or is it something else entirely?

  -- Don