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RX-Chain Noise Figure calculation with QPSS

Juanelin

Hi all,


I am currently simulating a receiver chain consistent of an LNA-Balun-Mixer combination using QPSS and QPNOISE as engines. My input port drives the LNA with a 50 Ohm impedance, while the output port serves as 100-Ohm load impedance to the mixer. So far, the gain of the complete Chain seems to correspond to the expectations (GAIN1+GAIN2+GAIN3) but the noise figure happens to be between around 3 dB higher than expected if I plug the single component gain/noise values into the Friis NF equation. I plot the NF using the "Noise Figure" option (SSB) under the QPNOISE results.

I was wondering if this 3 dB difference comes from the 100 Ohm output /50 Ohm input factor due to the single ended to differential conversion? So far I haven't found how the QPNOISE engine calculates the noise figure, but that would be my first guess. The receiver's building blocks are matched among them, 50 Ohm single ended, 100 Ohm for the differential ones, so I would discard at first instance any increase in the noise figure due to mismatch between components.


Any document or explanation would be greatly appreciated.


Thanks a lot,

Erick

Parents
  • Juanelin
    Hi Tawna,

    Many thanks for the reply. Please find below some answers to your questions.

    1- I am using IC 6.1.6/6.1.5 and MMSIM 15.1. Hotfix 6.27 I unfortunately cannot use IC 6.1.7 due to current incompatibilities with my PDK.

    2. My circuit is not a strong-nonlinear one. It is basically a LNA+Mixer chain with a single-differential conversion provided by an active balun. The engine I am using is Harmonic Balance with QPSS. Btw, I've already simulated the chain with HB and come to pretty similar results using HBNOISE.

    3. Will try to provide it. I will discuss it with my supervisor.

    4. I've found some information about the noise calculation in the document you mentioned, thanks a lot. I've found the following equations/definitions

    F = (No^2 - Nl^2)/Ns^2
    NF = 10*log10(F)

    where Nl = Noise at the output due to the output probe, Ns = Noise at the output due to the input probe, No = Total output noise. So if I understand correct, it is calculated using a typical ratio of power spectral densities (noise voltage square), but this power spectra depends on the actual load resistance vn^2 = 4kTR, where R is different for input (50) and output (100), so there is a factor 2 there that makes the noise figure ~ 3 dB higher. Please correct me if I misunderstood something.

    Many thanks for your help.

    Best regards,
    Erick
Reply
  • Juanelin
    Hi Tawna,

    Many thanks for the reply. Please find below some answers to your questions.

    1- I am using IC 6.1.6/6.1.5 and MMSIM 15.1. Hotfix 6.27 I unfortunately cannot use IC 6.1.7 due to current incompatibilities with my PDK.

    2. My circuit is not a strong-nonlinear one. It is basically a LNA+Mixer chain with a single-differential conversion provided by an active balun. The engine I am using is Harmonic Balance with QPSS. Btw, I've already simulated the chain with HB and come to pretty similar results using HBNOISE.

    3. Will try to provide it. I will discuss it with my supervisor.

    4. I've found some information about the noise calculation in the document you mentioned, thanks a lot. I've found the following equations/definitions

    F = (No^2 - Nl^2)/Ns^2
    NF = 10*log10(F)

    where Nl = Noise at the output due to the output probe, Ns = Noise at the output due to the input probe, No = Total output noise. So if I understand correct, it is calculated using a typical ratio of power spectral densities (noise voltage square), but this power spectra depends on the actual load resistance vn^2 = 4kTR, where R is different for input (50) and output (100), so there is a factor 2 there that makes the noise figure ~ 3 dB higher. Please correct me if I misunderstood something.

    Many thanks for your help.

    Best regards,
    Erick
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