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Simulators >> RF Simulators >> Pnoise transfer function different from PSS Vgain
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Message started by Bill Toole on Mar 28^th, 2007, 11:13am

Title: Pnoise transfer function different from PSS Vgain
Post by Bill Toole on Mar 28^th, 2007, 11:13am

While simulating differential LNA I noticed that the gain reported by the Pnoise Transfer Function is significantly different than the voltage gain from a straight PSS simulation. The particulars of the circuit are Zin = 100 Ohm, Zout = 800 Ohm, Av(unloaded) = 29.4dB. The input port is set 60dBuV (1mV). I deliberately mismatch the input and output with Rs=800 Ohm and RL = 100 Ohms. The PSS sim reports a voltage gain of 10.33dB as expected but the Transfer Function from the pnoise sim is -2dB??? I cannot find in the manual how Pnoise calculates the gain. Any thoughts? Why is the pnoise gain so different than the PSS gain?

Title: Re: Pnoise transfer function different from PSS Vg
Post by Frank Wiedmann on Mar 29^th, 2007, 12:04am

See the section "Gain Calculations in Pnoise" in Appendix L ("Using PSP and Pnoise Analyses") of the SpectreRF User Guide (http://sourcelink.cadence.com/docs/files/Release_Info/Docs/spectreRF/spectreRF6.1/appL.html) and also Solution 11184824 (http://sourcelink.cadence.com/docs/db/kdb/2005/June/11184824.html). These are also the first links that come up when you search for "pnoise gain" in SourceLink.

Title: Re: Pnoise transfer function different from PSS Vg
Post by Bill Toole on Mar 29^th, 2007, 8:17am

Thanks for the info. That helped Basically what it said is that the voltage gain is defined as Vout/Vin but the Noise gain is Vout/Vs so you have a badly mismatched case as I did with Rs=800 and Rin =100 there is an additional attenuation of the equivalent input noise source at the input of the DUT.