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CMOS 4007 filter and VCA

This little filter is something which I had built for fun, the idea is to use the MOSFET transistors of a 4007 as variable resistors. They are used with linearisation, and are even partly used " backwards ". For that to work the signal levels are attenuated so that within the circuit the levels at the MOSFETs is always lower than 600mV, to prevent conduction of the internal back diodes. (If you use higher levels than 5Vpp, you have to raise the input resistor proportionally.) This attenuation is reversed by the output VCA. So this means that you will have to use that after the filter.

The circuit configuration is state variable, as it is it has only linear control. The parts with regard to the control input are not dimensioned in the drawing. But as there are no established standards on linear frequency control voltages anyway, you will have to adapt them anyway.. Some good starting value might be 10k for these resistors and the trimmers.

CMOS Filter