vp1953 wrote on Sep 7th, 2010, 4:32pm:In the time domain the noise amplitudes (open circuit voltage) reach a peak of several mV
It is very natural result since you set Fmax = 20G.
Output Noise Voltage density is "4*k*T*R [Vrms
2/Hz]" since your output is an open circuit voltage of resistor.
So expected RMS output noise voltage is "sqrt(4*k*T*R*Fmax)=0.13mVrms
However peak voltage could be enough larger than 4*0.13mV=0.52mV
vp1953 wrote on Sep 7th, 2010, 4:32pm:spectrally there seem to be noise components that have magnitudes of -95 to -105dBm pretty much at all frequencies.
I think you are misunderstanding frequency bin width of FFT results.
vp1953 wrote on Sep 7th, 2010, 4:32pm:The schematic consists of simply a 50 ohm port left open (I also terminated the port with a capacitor without any improvement at the frequencies of interest).
This is also very natural result.
But time domain amplitude must be smaller.
See attached figures.
I can get reasonable results for both time domain noise and noise spectrum.
Here expected RMS output noise voltage is "sqrt(k*T*R*Fmax)=sqrt(k*290*50*0.5MHz)=0.32uVrms".
"Netlist for Agilent ADSsim" Quote:simulator lang=spectre
global 0
R1 (vo 0) resistor r=50 isnoisy=yes
R2 (vo 0) resistor r=50 isnoisy=no
simulator lang=ads
Options ResourceUsage=yes Verbose=yes UseNutmegFormat=no TopDesignName="data"
Options:Options1 Temp=16.85 Tnom=27 TopologyCheck=yes GiveAllWarnings=yes \
MaxWarnings=10
Tran:Tran1 StartTime=0 StopTime=10000u MaxTimeStep=1u IntegMethod=0 Mu=0.5 \
TimeStepControl=0 ChargeTol=1.0e-14 TruncTol=7.0 LimitStepForTL=yes \
ImpApprox=no ShortTL_Delay=1.0e-12 ImpMaxPts=4096 ImpRelTrunc=1.0e-4 \
ImpAbsTrunc=1.0e-7 ImpInterpOrder=1 ImpMode=1 ImpWindow=0 \
ImpNoncausalLength=32 CheckKCL=yes CheckOnlyDeltaV=yes MaxIters=10 \
MaxItersDC=200 StatusLevel=2 OutputAllPoints=yes \
NoiseBandwidth=1/(2*1u) NoiseScale=1 MaxOrder=4 HB_Sol=no HB_Window=no \
OutputPlan[1]="GlobalOutputPlan" OutputPlan[2]="GlobalInhibitPlan"
OutputPlan:GlobalOutputPlan Type="Output" UseBuiltinRule=no \
OverrideInhibitRule=no UseNodeNestLevel=yes NodeNestLevel=2 \
UseCurrentNestLevel=yes CurrentNestLevel=999 \
UseDeviceCurrentNestLevel=no NodeName[1]="vo"
OutputPlan:GlobalInhibitPlan Type="Inhibit" UseBuiltinRule=no \
OverrideInhibitRule=no NodeRegExpr[1]="\.net[0-9]+$|^net[0-9]+$"
"Netlist for Cadence Spectre" Quote:simulator lang=spectre
global 0
R1 (vo 0) resistor r=50 isnoisy=yes
R2 (vo 0) resistor r=50 isnoisy=no
simulatorOptions options temp=16.85 tnom=27 scalem=1.0 scale=1.0 \
gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 digits=5 cols=80 pivrel=1e-3 \
sensfile="../psf/sens.output" checklimitdest=psf
tran tran stop=10000u noiseseed=1 noisefmax=1/(2*1u) noisescale=1 \
maxstep=1u write="spectre.ic" writefinal="spectre.fc" annotate=status \
maxiters=5
save vo
saveOptions options save=selected