[Jeroen Belleman]

Bitrex wrote:
On 3/2/2011 8:06 PM, John Larkin wrote:
Actually, you can cascode a transistor into the source of a fet that
has a grounded gate. In that case, the source/collector voltage might
be a volt or two. You would have to look at the fet transfer curve,
and know the design operating current, to see exactly what that
voltage might be.

I'm foggy on how such a cascode reduces noise - improved distortion,
bandwidth, and PSRR I can understand but how does two transistors end up
less noisy than one? I know with tubes a cascode was considered a low
noise alternative since two triodes in cascode would have lower noise
than a single pentode, with similar gain.

As far as I can see, a cascode has the same noise as its bottom
transistor, near enough. The virtue of a cascode is that it
greatly reduces the effect of the Miller capacitance, so you
get more bandwidth and less input capacitance.

Jeroen Belleman