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Simulators >> RF Simulators >> Confusion about sidebands of Cadence Spectre's Pnoise
https://designers-guide.org/forum/YaBB.pl?num=1285083976

Message started by pancho_hideboo on Sep 21^st, 2010, 8:46am

Title: Confusion about sidebands of Cadence Spectre's Pnoise
Post by pancho_hideboo on Sep 21^st, 2010, 8:46am

When "sweeptype" is "absolute", noise_input frequencies of each sideband are calculated like following in Cadence Spectre's Pnoise.
Quote:

noise_input_freq = absolute_noise_output_freq +/- n*fund , ( n=0, +/-1, +/-2, +/-3, ...., +/-maxsideband )

Max sideband frequency is "maxsideband*fund" in this case.
There is no confusion about this.

However when "sweeptype" is "relative", I have confusions about sideband's treatment in calculation of total noise
in Cadence Spectre's Pnoise.
For example, consider following netlist.
Quote:

pss ( Vout 0 ) pss fund=1.0G harms=8 errpreset=moderate annotate=status

pnoise ( Vout 0 ) pnoise sweeptype=relative relharmnum=1
+ start=1 stop=10M dec=10 maxsideband=3 annotate=status
+ saveallsidebands=yes

Here noise_input frequencies of each sideband are calculated like following.
Quote:

noise_input_freq = (fund+relative_noise_output_freq) +/- n*fund , ( n=0, +/-1, +/-2, +/-3 )

(1) noise_input_freq(sideband= 0) = +1GHz + relative_noise_output_freq ; This is a feedthrough noise. This contributes to USB.
(2) noise_input_freq(sideband=-1) = relative_noise_output_freq ; Up conversion noise from around DC. This contributes to USB.
(3) noise_input_freq(sideband=+1) = +2GHz + relative_noise_output_freq ; Down conversion noise from around 2*fund. This contributes to USB.
(4) noise_input_freq(sideband=-2) = -1GHz + relative_noise_output_freq ; This is a feedthrough noise. This contributes to LSB.
(5) noise_input_freq(sideband=+2) = +3GHz + relative_noise_output_freq ; Down conversion noise from around 3*fund. This contributes to USB.
(6) noise_input_freq(sideband=-3) = -2GHz + relative_noise_output_freq ; Down conversion noise from around 2*fund. This contributes to LSB.
(7) noise_input_freq(sideband=+3) = +4GHz + relative_noise_output_freq ; Down conversion noise from around 4*fund. This contributes to USB.

Here my questions are :
(a) What is an actual max sideband frequency in this case ?
Is it "(maxsideband+1)*fund=4*fund=4GHz" ?

(b) Numbers of evaluated noise_input frequencies of sideband are asymmetrical about DC.
For example, "-2GHz, -1GHz, 0Hz, +1GHz, +2GHz, +3GHz, +4GHz" in the above case.
Noise calculated by Cadence Spectre is a Single Sided PSD regardless of "freqaxis expression".
For example, noise voltage spectrum density of open circuit Resistor is "4*k*T*R [Vrms²/Hz]" not "2*k*T*R [Vrms²/Hz]" regardless of "freqaxis expression".

Actually Cadence Spectre's Pnoise don't use (4) and (6) for calculation of total noise ?