I can't find out any problem in your post. Your post is not design issue but just very simple common usage of simulator.
Jack wrote on Feb 16th, 2009, 3:30am:I am simulating a Gilbert Multiplier. When I start with the noise figure simulation, the results is 140dB. This result is a little carzy.
Maybe you are wrong in analysis setting. Do you understand DSB_NF, SSB_NF(USB or LSB) correctly ?
What value is conversion gain ?
Jack wrote on Feb 16th, 2009, 3:30am:Because I am not familiar with PSS simulation and QPSS simulation, which one should I use, how can I set up the parameters?
It depend on your needs.
PSS is a expansion by single frequency basis while QPSS is a expansion by multiple frequency bases which have no common divisor frequency each other.
If your questions are usages of very specific EDA vendor's simulator, post to "The Designer's Guide Community Forum ≫ Simulators ≫ RF Simulators".
Jack wrote on Feb 16th, 2009, 3:30am:For mixer, I think if the switching transistor does not contribute the noise, the analysis is similar with the common-source cascade LNA.
No, you are wrong.
Jack wrote on Feb 16th, 2009, 3:30am:But for multiplier, the switching transistor also contributes the noise, but for the input transistor of RF signal, its noise is mainly common-mode noise at the output of multiplier because the input transistor of template signal is always working in saturation region.
What do you mean by "template signal" ?
Jack wrote on Feb 16th, 2009, 3:30am:But I think mixer is a little different from multiplier.
You mean a difference of Gilbert Cell
as four quadrant multiplier
and
as mixer such as down converter or up converter ?
But there is no difference about treatment of them in simulation, even though they works as multiplier or mixer.
Jack wrote on Feb 16th, 2009, 3:30am:So in this case, how can I simulate the noise figure correctly?
What do you confusing ?
Jack wrote on Feb 16th, 2009, 3:46am:Also, for Mixer, the LO signal is a frequency-fixed signal,
Not, correct. Rather fixed frequency of LO is rare in mixer application.
Jack wrote on Feb 16th, 2009, 3:46am:but for Multiplier, the template signal is the same one with the RF input signal for coherent detection.
What do you mean ?
I think this is zero-IF mixer or matched detection.
Anyway there is no difference about treatment in simulation.