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pnoise spurs at multiples of clock frequency.

vamshiky

Hi,

 I have a simple inverter driven by a square wave, and ran pnoise on the circuit.

There is flicker and thermal noise and after that  has huge spurs ( about +20dBc ) at 2*Ffref , 5*Fref.

And this goes away if I carefully choose the sweep type and step size (delberately avoiding those freq points during sim). 

 

Also I have noticed from earlier posts that while running pnoise sim, simulator automatically skips the freq point which is exact multiple of beat frequency and gives a message "Infinite flicker noise is ignored"

however I dont see this happening in my sims.

Are there any additonal settings/options which I missed out.

 

Thanks,

Vamshi 

 

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  • Andrew, Here is the netlist, and spectre is : sub-version 12.1.0.489.isr9 ---------------------------- // Generated for: spectre // Generated on: Dec 19 12:31:13 2013 // Design library name: xxxx // Design cell name: test_pss_pnoise // Design view name: schematic simulator lang=spectre global 0 include "xxxxx.scs" // Library name: xxxxxxxxx // Cell name: CKINVX2 // View name: schematic subckt CKINVX2 VDD VSS i o MN0 (o i VSS VSS) nch_lvt ..................... MP0 (o i VDD VDD) pch_lvt ...................... ends CKINVX2 // End of subcircuit definition. // Library name: xxxx // Cell name: test_pss_pnoise // View name: schematic V1 (avss 0) vsource dc=0 type=dc V0 (avdd0p8 avss) vsource dc=800.0m type=dc I1 (avdd0p8 avss in out) CKINVX2 V2 (in avss) vsource type=pulse val0=0 val1=800.0m period=20n delay=10p \ rise=10p fall=10p width=10n C0 (out avss) capacitor c=10f simulatorOptions options reltol=1e-3 vabstol=1e-6 iabstol=1e-12 temp=27 \ tnom=27 scalem=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 digits=5 \ cols=80 pivrel=1e-3 sensfile="../psf/sens.output" checklimitdest=psf pss pss fund=50M harms=10 errpreset=conservative + annotate=status pnoise ( out avss ) pnoise start=1k stop=500M dec=20 + maxsideband=10 annotate=status modelParameter info what=models where=rawfile element info what=inst where=rawfile outputParameter info what=output where=rawfile designParamVals info what=parameters where=rawfile primitives info what=primitives where=rawfile subckts info what=subckts where=rawfile save out avss saveOptions options save=selected -------------------------------------------------------------------------- In this example I get tones at 100M,500M with -1.7dB magnitude, and & noisefloor is <-150dB. Not sure if can give the device details at the moment, so removed those lines here... Thanks, Vamshi
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  • Andrew, Here is the netlist, and spectre is : sub-version 12.1.0.489.isr9 ---------------------------- // Generated for: spectre // Generated on: Dec 19 12:31:13 2013 // Design library name: xxxx // Design cell name: test_pss_pnoise // Design view name: schematic simulator lang=spectre global 0 include "xxxxx.scs" // Library name: xxxxxxxxx // Cell name: CKINVX2 // View name: schematic subckt CKINVX2 VDD VSS i o MN0 (o i VSS VSS) nch_lvt ..................... MP0 (o i VDD VDD) pch_lvt ...................... ends CKINVX2 // End of subcircuit definition. // Library name: xxxx // Cell name: test_pss_pnoise // View name: schematic V1 (avss 0) vsource dc=0 type=dc V0 (avdd0p8 avss) vsource dc=800.0m type=dc I1 (avdd0p8 avss in out) CKINVX2 V2 (in avss) vsource type=pulse val0=0 val1=800.0m period=20n delay=10p \ rise=10p fall=10p width=10n C0 (out avss) capacitor c=10f simulatorOptions options reltol=1e-3 vabstol=1e-6 iabstol=1e-12 temp=27 \ tnom=27 scalem=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 digits=5 \ cols=80 pivrel=1e-3 sensfile="../psf/sens.output" checklimitdest=psf pss pss fund=50M harms=10 errpreset=conservative + annotate=status pnoise ( out avss ) pnoise start=1k stop=500M dec=20 + maxsideband=10 annotate=status modelParameter info what=models where=rawfile element info what=inst where=rawfile outputParameter info what=output where=rawfile designParamVals info what=parameters where=rawfile primitives info what=primitives where=rawfile subckts info what=subckts where=rawfile save out avss saveOptions options save=selected -------------------------------------------------------------------------- In this example I get tones at 100M,500M with -1.7dB magnitude, and & noisefloor is <-150dB. Not sure if can give the device details at the moment, so removed those lines here... Thanks, Vamshi
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