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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 

 

Parents

  • I tried your circuit (with two pnoise analyses in the netlist to make it simpler), and with some made up models and device sizes, and I don't see the problem. Spectre also reports (using the same version you're using):

     Warning from spectre at freq = 100 MHz during PNoise analysis `pnoise'.
        WARNING (SPCRTRF-15037): Infinite flicker noise is ignored. 

    Here's what I used (I fixed your line wrapped netlist - I assume you're using Chrome, which causes some problems with the forums on this web site, as far as I know).

     // 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"
    model nch_lvt bsim4 type=n
    model pch_lvt bsim4 type=p
    // Library name: xxxxxxxxx
    // Cell name: CKINVX2
    // View name: schematic
    subckt CKINVX2 VDD VSS i o
    MN0 (o i VSS VSS) nch_lvt w=1u l=0.1u
    MP0 (o i VDD VDD) pch_lvt w=2u l=0.1u
    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
    pnoiseAlt ( out avss ) pnoise start=1k stop=501M step=1.7M
    + 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

    Regards,

    Andrew.

Reply

  • I tried your circuit (with two pnoise analyses in the netlist to make it simpler), and with some made up models and device sizes, and I don't see the problem. Spectre also reports (using the same version you're using):

     Warning from spectre at freq = 100 MHz during PNoise analysis `pnoise'.
        WARNING (SPCRTRF-15037): Infinite flicker noise is ignored. 

    Here's what I used (I fixed your line wrapped netlist - I assume you're using Chrome, which causes some problems with the forums on this web site, as far as I know).

     // 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"
    model nch_lvt bsim4 type=n
    model pch_lvt bsim4 type=p
    // Library name: xxxxxxxxx
    // Cell name: CKINVX2
    // View name: schematic
    subckt CKINVX2 VDD VSS i o
    MN0 (o i VSS VSS) nch_lvt w=1u l=0.1u
    MP0 (o i VDD VDD) pch_lvt w=2u l=0.1u
    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
    pnoiseAlt ( out avss ) pnoise start=1k stop=501M step=1.7M
    + 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

    Regards,

    Andrew.

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