hi,
any one can tell me how to calculate the noise figure for a cascade
series of stages given the noise figure and power gain for the
individual stages.
and what is da order of the amplifiers which have different gains and
noise figure which have lowest overall noise figure.
bye
thx

On 1 Dec 2006 08:24:27 -0800, "esampathj" wrote
in .com:

hi,
any one can tell me how to calculate the noise figure for a cascade
series of stages given the noise figure and power gain for the
individual stages.


The overall noise figure is a complex function of each stage and their
respective gains. But for practical purposes it is equivalent to the
noise of the first stage -provided- the amplification of each stage is
sufficient to exceed the noise figure of each successive stage. I.e,
assuming these are current amplifiers, if the noise current of the
first stage is 1pA and the noise current of the second stage is 10pA,
then the amplification of the first stage needs to be 10 or greater
for the overall noise current to be 1pA, regardless of the second
stage noise.

Of course the noise figure of any amplifier depends upon the circuit
configuration, component selection and quality, etc.

and what is da order of the amplifiers which have different gains and
noise figure which have lowest overall noise figure.


The stage with the lowest noise goes in front, which will usually be
the stage with the lowest gain (generally, gain = noise).


bye


L8r.


thx


You're welcome.