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N-Path Mixer NF (Read 133 times)
strawberries52
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N-Path Mixer NF
Apr 13th, 2021, 10:24pm
 
Hello,

This is my first post on the forum! I am a student so thank you and bear with me.

I am working on an 8-path mixer design, and trying to measure the Noise Factor. I am using a LO of 2.485GHz.

Currently, the bandwidth of the mixer is right, it appears that S11 is about -26 dB, I believe the design seems OK.

I am having trouble getting results that seem right for NF using pnoise analysis in Cadence.

I'm not sure the correct way to do this - it seems that for a downconversion mixer you usually use -1 as refSideBand, but that doesn't make a lot of sense here, since the LO and RF frequencies are equal.

When I set the refSideBand to -1, with the beat frequency set as 2.485GHz and measure NF at baseband, the NF is really high, like 10-20 dB which seems way too high!

I've attached some photos of the schematic, my simulation results, the schematic (it only shows a few of the 8 paths) and the pnoise analysis setup.

Any tips would be appreciated.
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strawberries52
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Re: N-Path Mixer NF
Reply #1 - Apr 13th, 2021, 10:24pm
 
I realized it will only allow me attach one image per post.
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strawberries52
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Re: N-Path Mixer NF
Reply #2 - Apr 13th, 2021, 10:25pm
 
.
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Ken Kundert
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Re: N-Path Mixer NF
Reply #3 - Apr 14th, 2021, 5:26pm
 
Ignore the term 'beat frequency'.  This was a misnomer that was put into ADE from the very first days of SpectreRF and was never fixed.  The proper term is 'fundamental frequency'.

In your case the fundamental frequency is the LO frequency (2.485 GHz).

The PNoise choose analysis form helpfully indicates that the refsideband can be computed with: |Fin| = |Fout + refsideband*Ffund|.  I think this formula should not have absolute value bars.  In that case, Fin = 2.485 GHz, Fout = 0 Hz, and Ffund = 2.485 GHz, so refsideband would be 1.  This makes sense because the refsideband is the LO harmonic that the input signal is mixing with to produce the output signal.

-Ken
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