[sdiy] CMOS as voltage variable resistor

[Grant Richter]

Just a thought, I noticed the thread on CMOS with variable resistance.

In theory, as the control pin voltage goes from 0 to +V, the transmission
gate (TG) resistance changes from very large to quite small. The problem is
the control voltage to resistance curve is deliberately very non-linear.

Since 4016/66s should be monolithically matched, you could put one TG inside
the feedback loop of an op-amp to linearize the resistance curve. Fed from
the same op-amp output as the linearizing TG, the other sections should show
a linear change in resistance to control voltage, within limits of their
voltage dependence.

This could be useful for building envelope generators. Most envelope
generators have a manual resistance in series with a TG switch. Using TGs as
voltage variable resistances, you could use the TGs both for current
steering and charging rate control into the capacitor.