improoving SNR of OTA ?

[Martin Czech]

> We all know that one can improove the SNR of a transistor by connecting
> several ones in parallel, or the SNR of a diode (as VC Resistor) by
> connecting several ones in series.
> Now what about this: Build a differential pair with variable tail current
> (i.e. core of OTA), and connect 10 diodes in series with each emitter.
> This would allow 11 times larger input levels, but the noise of each
> element would only contribute in a geometric (and not arithmetic) law.
> This would only work if the noise of a diode and the noise of a transistor
> would be the same order of magnitude. No idea if this is the case or
> not. Anybody knows for sure ?
> 
I know that emitter resistors in diff stages introduce feedback,
ie. lower gain, thus allowing higher input levels making SNR
better. The (terrible) schematic of my discrete 4-quadrant-multiplier
uses this method. The resistors won't introduce much noise.
Maybe I don't get the point, but why using diodes as "resistors"
with all disadvantages when you're allready going discrete and have
good resistor? I don't think that the diodes will linearize anything
in your circuit. 

m.c.