Re: Hyperbolic tangent transfer function

On Tue, 10 May 2005 12:49:34 -0400, John Popelish <jpopelish@xxxxxxxx> wroth:

>James Meyer wrote:
>>
>> If I wanted to synthesize an arbitrary monotonic function, I'd start
>> with a string of diodes and resistors. PWL. Not piece-wise linear, but
>> piece-wise logarithmic.
>
>Then I have to control temperature of those diodes or correct the
>result for temperature variations. At least the PWL version can e
>pretty stable. But either of these is more complicated than the
>transconductance amplifier, I think. My difficulty is quantifying the
>precision of the transconductance amplifier. If I had a temperature
>controllable differential pair, I could use opamps to form the rest of
>the circuit, and eliminate most of the tolerances.

If size isn't a big concern, a small circuit board (or stack of two
boards) with the diode/resistor string and a resistive heater and a thermistor
placed in a styrofoam container could do the job. You'd then have access to all
the internal circuitry to tweak to your heart's content. A cube 2 inches on a
side would probably be big enough. OCXO's are about the same size.

Jim


.

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