[sdiy] Auto Center waveforms

[Forbes, William ALGLSG-LXES]

Simply integrate the waveform over many cycles. Large RC value in the
integrator. This gives the DC component.
Simply subtract the level from the waveform.
There is no need to sync the integration with the period of the
waveform.
I've seen this done on some CD players. This avoids putting the audio
path through a cap.

Bill Forbes.
  

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Jerry
Gray-Eskue
Sent: 14 July 2009 14:46
To: Synth-diy at dropmix.xs4all.nl
Subject: [sdiy] Auto Center waveforms


I have been thinking about centering arbitrary wave shapes on 0 volts.

Wave shapers and some VCO waveforms tend to create waveforms with a dc
offset and it would be nice to have a circuit that would "balance" these
so that the sum of the + voltage = the sum of the - voltage.

To do this it would seem that if you took the sum of one waveform cycle
using a simple integrator you would have a voltage that represents the
DC offset. Using the proper scaling you could then subtract this voltage
from the waveform to remove the offset. A pair of voltage hold circuits
would store the voltage of the previous cycle and remove the offset from
the current cycle. The integrator (s) would reset each cycle after the
voltage hold circuits were updated.

The problem that I am having with this scheme is that it appears the
period of the waveform must be used to scale the resulting voltage. Now
it is simple enough to use a constant current into a second integrator
to derive a voltage representing the time period, and it would appear
that using this voltage and a multiplier in the feed back of an op amp
will allow division of the total voltage / period voltage.

The issue with this approach is cost and complexity. It seems like there
may be a "Slick" way to do this without resorting to expensive ICs and
still give good offset removal performance.

Any thoughts, or ideas on a better method ?

- Jerry

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