Dear experts,

I am trying to simulate a mixer that upconverts flicker noise. Fig(a) in the attachment shows the schematic of the circuit. in,f and in,t are flicker and thermal noise sources modeled in verilogA. fclk is 2.5kHz. Fig(b) is the output voltage noise PSD obtained through pnoise analysis using spectreRF. My question is about the peaking at 10kHz. While I understanding that mixer upconverts flicker noise to all odd harmonics of fclk, I expected the fundamental to be larger than any other harmonic. But it turned out not to be the case, at least in this simulation.

I also used Mentor graphics afs to simulate the circuit with same pnoise settings and obtained Fig(c),  and it does not exhibit such peaking. The spot noise at low frequencies match between spectreRF and afs.

The following are my questions:
1. Is the peaking seen in simulation due to the fact that I do not specify specific points where the analysis needs to be run? I noticed dominant peaking happen at 2.5kHz when I add 2.5kHz and its harmonics as specific points where pnoise needs to be run. This was expected as flicker has infinite power at zero frequency. (Similar explanation was provided at https://community.cadence.com/cadence_technology_forums/f/custom-ic-design/28660...
/regarding-pss-and-pnoise-analysis-getting-a-peak-at-1khz-in-noise-plot)

2. As can be seen, spectreRF and afs spot noise values are also in agreement at 2.5kHz but not at other harmonics of fclk. Is this just a coincidence? (Ideally I would have expected both to give a spot noise fclk that is very large).

Thanks and regards

Thanks Ken, for the quick response. It is really helpful. Another issue that I experienced was the frequency at which the peaking was observed. As mentioned earlier, I used 2.5kHz clk and 10kHz, where the peaking was observed is not an odd multiple of fclk. As in attached Fig(a), one can see peaking at 10kHz with a fclk of 2.5kHz. When I changed fclk to 2kHz (Fig.(b)), I see peaking at 10kHz but this was expected being a odd harmonic. The clk phases are non-overlapping and have nearly 50% duty ratio.

Is there something that I am missing in this sim/setup?

Thanks and regards

PS: I noticed that figures in my previous post were awful. Sorry about that.

Thanks Ken, for clarifying. Indeed I would expect to see smaller peaks at even harmonics to account for the minor asymmetries but sometimes the peaks are larger than any other harmonics, odd included, which surprised me.

Best regards