Tracking Generators

gstopp at fibermux.com gstopp at fibermux.com
Mon Jan 22 17:08:35 CET 1996


     Brilliant!
     
     I was envisioning several full-wave rectifiers, each with its own 
     offset amplifier, and then was thinking "there must be a way to 
     simplifiy it", and then went on to other things....
     
     I suppose you just tie all of the 3080 outputs together for current 
     summing also. Now I am starting to think that this module may be well 
     worth the construction effort! Can you post an ASCIImatic of the 
     transistor rectifier to pin 5 of the 3080? I am most curious.
     
     And like you, I never use slide pots in my homemade designs. Round 
     holes are just too easy to drill.
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: RE: Re[2]: Tracking Generators
Author:  Haible_Juergen#Tel2743 <HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de>
at ccrelayout
Date:    1/22/96 11:05 AM


>     However the "interpolating scanner" concept that Juergen has 
>     implemented sounds like a quite useful way to generate
>     time-independent non-linear transfer functions, using crossfading
>     VCA's to "morph" between the steps. It seems to me that you would need 
     
>     to convert the input sweep voltage to a series of trapezoidal 
>     functions that are staggered in level (is this how you do it, 
>     Juergen?).
     
Exactly. Just the good old one-transistor sawtooth-to-triangle-converter. 
Using a PNP for the right polarity, the collector current directly feeds the 
OTA Iabc input. The base of each transistor is controlled by an opamp
which adds the  input voltage and a different offset voltage for each 
stage. The positive Rail, to which the emitter resistors go, is stabilized 
at approx. 10V. It can be fine adjusted to give exactly the desired overlap 
of the different triangle windows.
If I would have used sliders instead of pots (can't make these long holes), 
I really could draw the waveform with the sliders. The sanner makes a 
piecewise linear interpolation between the points set by the pots.
With a sequencer or comparator method, You would get a staircase
funktion instead of a piece wise linear  function. Even with a linear Slew 
Limiter You would have to control the time constant by *both*, the input 
frequency, *and* the difference between two adjacent levels to get similar 
result! But even then, this concept is bound too loose when You come near 
very low frequencies.
     
JH.




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