[sdiy] CMOS V.C.R. with 1V/Oct Response

[Grant Richter]

Groovy!

What a great design! Nice job Mike!

One question that springs to mind is the signal levels. Will the resistors
tolerate swings below Vss? Or does the signal voltage have to remain above
Vss?

Electronotes #81 Page 8 has an article "A Design for a New Multi-Mode
Voltage Controlled Filter" (the so-called "Dual Shift" filter) which shows
implementing the equivalent of a state variable using all-pass sections. The
all-pass sections are controlled by variable resistors to ground. This would
seem to be an ideal application for this control circuit.

Also the general design of an all-pass network is much simplified by this
control design. I suspect only one Master FET would be needed, even
uncompensated 4049s should track well enough for a phase shifter. That would
require only 3 x 4049s to make a 16 pole phase shifter.

> From: eq927 at freenet.carleton.ca
> Date: Fri, 03 May 2002 20:04:00 -0400
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] CMOS V.C.R. with 1V/Oct Response
> 
> Hello List,
> Osamu Hoshuyama kindly provided webspace for a schematic of a circuit I
> built earlier this year. It is a design for a multiple
> CMOS voltage-controlled resistor where the resistance is constrained to
> be an exponential function of the applied control voltage. The schematic
> is here:
> 
> http://www5b.biglobe.ne.jp/~houshu/synth/mike_irwin/cmos-vcr.gif
> 
> Regards, Mike
>