Post subject: Impact of Noise Figure on Phase Noise
Posted: Fri Jul 22, 2005 3:03 pm
Lets say you have a signal at a known frequency
with a known amount of phase noise, and you pass
the signal through a fixed attenuator, is there
a way to calculate/estimate what impact the attenuation
has on the phase noise of the output signal?
Posted: Sun Jul 24, 2005 11:30 am
Joined: Sun Aug 03, 2003
2:02 pm Posts: 653 Location: Erie, PA
My guess is that the effect
of the attenuator on phase noise would be similar
to the intended signal and noise. You would need
to perform a cascade analysis for the path where
the phase noise is first injected and treat that
component of the total signal as a separate signal
that is summed with the intended signal.
The discrete phase noise component would be attenuated
by an amount equal to the total Gain in the path
from the phase noise injection point and the continuous
phase noise component would be subject to the total
Gain and Noise Figure.
If the phase noise
is present on the signal at the system input, then
it is treated to the same effects as the rest of
the intended signal and noise.
If it is injected
in an LO at a mixer, then the phase noise component
is determined by a separate cascade comprised by
the path the LO signal takes.
In the last
case, for a real system the summation of the two
components [(intended signal + noise] + [LO + phase
noise)] would be a point-by-point vector addition,
so a simple scalar summing could produce erroneous