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Simulators >> RF Simulators >> how to do mixer pac & pnoise, when its input is large signal?
https://designers-guide.org/forum/YaBB.pl?num=1393213315

Message started by baohulu on Feb 23^rd, 2014, 7:41pm

Title: how to do mixer pac & pnoise, when its input is large signal?
Post by baohulu on Feb 23^rd, 2014, 7:41pm

I have done a mixer, its lo and input is tied together to a sinewave with large peak when it is used

but in simulation its performance, how to do the pac and pnoise accurately? I use two method:
1. I do pac & pnoise just as normal: input is connected to a port with dc type and pac setting to 1, lo is connected to a port with sinewave type and pac setting to 0, then do pss, pac & pnoise
2. just as its practical application, I connected input and lo pin together to a port with sinewave type setting its pac=1, then do pss, pac and pnoise?

the two simulations results are below:
for pac: they are nearly the same
for pnoise: they are totally different, I see bias noise is the largest in 2nd method, it may be because the circuit bad balance when input is large signal. in 1st method, the largest is mixer input

I know pac is a small-signal simulation method, when I connected input with a large signal as in 2nd, is the pac simulation results right?
pnoise is not a small-signal simulation method, so , if the 2nd simulation is right? and the 1st simulation of pnoise not considered the linearity caused by the input large signal.

anyone knows the right simulation method when the mixer input is connected to a large signal as above?

Title: Re: how to do mixer pac & pnoise, when its input is large signal?
Post by Ken Kundert on Feb 25^th, 2014, 1:23am

Both PAC and PNoise are considered small-signal analyses.

Title: Re: how to do mixer pac & pnoise, when its input is large signal?
Post by baohulu on Feb 25^th, 2014, 2:01am

if I give mixer a large signal, which will make the mixer linearity very poor, how can I simulate its noise at this case?

Title: Re: how to do mixer pac & pnoise, when its input is large signal?
Post by Ken Kundert on Feb 25^th, 2014, 2:00pm

You would apply the input signal in the underlying PSS (or QPSS) analysis. In PNoise analysis, the noise is always small.

-Ken

Title: Re: how to do mixer pac & pnoise, when its input is large signal?
Post by RFICDUDE on Feb 26^th, 2014, 6:06pm

How nonlinear is the circuit under the test conditions you are interested in simulating? Specifically, what is the dBc difference between the desired signal and the intermodulation or harmonic distortion components of the mixer?

You could also consider using transient noise analysis to provide you with noise information when large signals are present, but you have to be careful setting up the simulation and interpreting the FFT results. The down side is that transient noise doesn't provide you with a means to separate noise contributions from different sources.