[sdiy] What makes a transistor "low noise"?

[Samuel Morse]

In "Analysis and Design of Analog Integrated Circuits" by Gray and Meyer
there is a detailed discussion of the different noise properties of
transistors in chapter 11. I'm sure there are whole books on the subject.
There are many different causes of noise, shot, thermal, flicker, popcorn,
and avalanche, to name some. Noise is usually measured in terms of a whole
circuit because feedback and other techniques can drastically effect the
noise figure of a particular amplifier.

-Sam

-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Metrophage
Sent: Friday, November 05, 2004 8:31 AM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] What makes a transistor "low noise"?


As I BEGIN to understand how transistors work, I wonder about this. I
often see op-amps labelled as being less noisy than general-purpose
types, but typically not for transistors. Still, I have heard that some
are noisier than others.

What is it about transistors which would indicate that they would or
would not distort signals somehow? How are such factors reflected in
the specs which are usually offered?

Through my time of synth reading, I feel I have a rough idea of what
makes some op-amps more or less suitable for a given application. Not
yet so with transistors though! I'd be psyched to hear some info and
opinions on this.
CJ



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