[sdiy] Operational Transconductance Amplifiers

[David Moylan]

Antti Huovilainen wrote:
> On Tue, 9 Mar 2010, Andre Majorel wrote:
> 
>> "An OTA is basically a two quadrant multiplier. It multiplies an
>> input voltage by a control current and produces a current as its
>> output. The OTA's transfer function is that of a differential
>> transistor pair, which is pretty convenient, although, a bit tough
>> to analyze."
> 
> Or to put it in very basic maths:
> Iout = Iabc * tanh(Vin / 2Vt)
> Vt = ~26mV (kT/q)
> 
Is the tanh response the reason why the differential input voltage has a 
very small (linear) range?

Is there a certain transistor arrangement in the amp that gives it this 
response or is it an innate transistor phenomenon?

Dave

> No need to bother with gm or unexplained constants.
> 
> Antti
> 
> "No boom today. Boom tomorrow. There's always a boom tomorrow"
>   -- Lt. Cmdr. Ivanova
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