[sdiy] Continously Variable Symmetry Triangle

[ASSI]

On Tuesday 08 July 2003 09:46, Don Tillman wrote:
> I don't know what the significance of the sum of both currents means
> to the linearity of the modulation.

The sum of both currents tells you the modulation depth. I haven't 
shown the derivation of (2), but if the sum current follows that curve, 
the symmetry modulation is linear with respect to the (normalized) 
modulation CV.

> So I think you can
> compensate for this nonlinearity exactly by preceeding the circuit
> with an anti-diff-amp (a diff amp in the feedback loop of an opamp).

Feedback topologies are fun, but I thought it was especially neat that 
I would not need anything like that.

> So I would recommend deriving a PWM square wave at the same time and
> linearizing the control voltage only if the circuit is going to be
> used as an LFO.

The loop filter would probably be a bear to design, although it might 
work at the relatively low frequencies of an LFO (perhaps with a 
replica oscillator at a scaled up frequency for the PWM generation). 
Please note that the gain/expo/attenuation configuration I described is 
easily used to modulate between "slow" and "fast" modulation, 
potentially even under voltage control.


Achim.
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