[sdiy] ota's as gates.

[mirwin at qouest.net]

One way to ensure the OTA is completely shut off is to use a saturated
open-collector transistor switch to short the Iabc pin to the (-)15V
rail. The Iabc current will be shunted away from the Iabc pin, and the
transistor will have a saturation voltage of only a few tens of mV
(unless you use a bad one or the transistor is not saturated). The base
of the transistor can be current-driven if you want the control signal
to be ground-referenced. An alternative is to use the output of a LM393
or LM339 dual or quad comparator, which has a low saturation voltage and
low leakage current (if there is already one elsewhere in the circuit,
and only part of the chip is being used).
Regards, Mike