Quadrature VCO Module finished

[gstopp at fibermux.com]

     My question exactly. Don beat me to it. It looks like you have two 
     tri-square generators linked together somehow to get a 90 degree phase 
     difference regardless of frequency. I would presume that they have 
     identical currents from the exponential converter (BTW what kind of 
     expo converter are you using?). Perhaps the zero-crossing of one 
     triangle is used to reverse the direction of the other triangle, like 
     my tri-square sync idea?


______________________________ Reply Separator _________________________________
Subject: Re: Quadrature VCO Module finished
Author:  don at till.com at ccrelayout
Date:    9/8/95 11:39 AM

   >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