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Design >> RF Design >> NF simulation using out-of-band blocker (SpectreRF)
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Message started by Guilherme Theis on May 21^st, 2019, 6:56am

Title: NF simulation using out-of-band blocker (SpectreRF)
Post by Guilherme Theis on May 21^st, 2019, 6:56am

Hello,

I should start saying I know basics from SpectreRF simulations. I am simulating a wideband LNA with a switched capacitor filter. While I can see my harmonic response, NF, S11, IIP3 using PSS+PSP simulation I would like to know how I can properly simulate my circuit to see how a 0 dBm blocker at 20 MHz can affect it (GSM).

My circuit uses a Sine Port in the input and a DC port in the output (I can draw you the schematic if you need it but I can't get the pictures/data because of security constraints in the lab I am doing my master's thesis).

I have see this tutorial, but is about mixers and I don't know how to translate it to my circuit. https://filebox.ece.vt.edu/~symort/rfworkshop/Mixer_workshop_instruction.pdf

Title: Re: NF simulation using out-of-band blocker (SpectreRF)
Post by Ken Kundert on May 21^st, 2019, 6:52pm

Switched capacitor filter? I have no idea why you would have a switched capacitor filter in this simulation, but its clock will cause a lot of problems. You should eliminate it if you can.

Conceptually an LNA with a blocker is very much like a mixer where you are interested in the direct transmission path (no frequency conversion). In this case the blocker plays the role of the LO. So apply the blocker as a large sinusoid on the input. Apply the input signal as a small stimulus (using pacmag), also on the input. Run PSS at the blocker frequency. Run PAC at the input frequency and set the sideband to 0.

-Ken

Title: Re: NF simulation using out-of-band blocker (SpectreRF)
Post by Horror Vacui on Jul 24^th, 2019, 1:35am

I would like to give big thumbs up to Ken's answer. It is so eloquent, high level for understanding, and very practical at the same time. These are the things in this community what I love! ;)