[sdiy] Auto Center waveforms

[Jerry Gray-Eskue]

I know there are some guys out there with a heavy math background (including
at least one PHD)

How about this approach, I use a Differentiating Amplifier to calculate the
Derivative of the input signal and take that output (the Derivative) into an
Integrating Amplifier to recreate the signal without the DC component.

It is in the simplest form just 2 op amps 2 caps and 2 resistors and runs
Real Time with no significant delays.

Is it mathematically sound?




-----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: Tuesday, July 14, 2009 8:46 AM
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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