The Designer's Guide Community Forum https://designers-guide.org/forum/YaBB.pl Measurements >> Phase Noise and Jitter Measurements >> Jitter in Limiting Amplifier https://designers-guide.org/forum/YaBB.pl?num=1059089369 Message started by Hans on Jul 24th, 2003, 4:29pm

 Title: Jitter in Limiting Amplifier Post by Hans on Jul 24th, 2003, 4:29pm I have a question regarding the way PNoise simulates sampled noise (tdnoise). Let's say we have a limiting amplifier that is stimulated with a sinusoid at frequency fo. The amplifier clips the signal into somewhat of a square wave and the output will be accompanied by the noise generated within the amplifier. This signal is then presented to some logic block with logic threshold VTH,LOGIC. The general idea is to run a tdnoise simulation and look at the noise voltage at the output when the output signal crosses VTH,LOGIC. When plotting the integrated output noise voltage the SpectreRF User Guide suggest using the range from zero to the PSS fundamental frequency. Does this mean that the PSD for a sampled time point is only integrated over that interval? Or is the computation done in the time domain from zero to 1/fo? How are frequencies above the fundamental taken into account? (i.e. what exactly is being integrated?) The following quote from the Affirma RF Simulator (SpectreRF) User Guide (Product Version 4.4.6 - April 2001) is the source of my confusion:"Type 0 as the start frequency and the PSS fundamental frequency as the stop period. For example, type 1G if the PSS period is 1ns." (p. 909).I would really appreciate it, if someone could clarify this for me. So far the Cadence documentation has been rather vague yet I believe someone out here must have stumbled across the same problem. Thanks in advance, Hans

 Title: Re: Jitter in Limiting Amplifier Post by pancho_hideboo on Jul 28th, 2003, 8:08am Description about TDnoise in SpectreRF manual is wrong. :'(TDnoise setting has to be like following.(1) Sweep Range for Pnoise.This should be from 0 to PSSfund/2.Sweep Range is the one we fill in the PNoise analysis form. For regular pnoise(noisetype=source), the range could be from 0 to any frequency we want.For time-domain pnoise (noisetype=timedomain), the range should be from 0 to PSSfund/2.Time-domain noise PSD is periodic with PSSfund so PSD is symmetric around PSSfund/2. (2) Frequency Integration Range of PSD. This should be from 0 to PSSfund/2.For time-domain noise (noisetype=timedomain), SpectreRF calculates the PSD of the discrete (or sampled) noise at t0+n*T (T=1/PSSfund, 0<=t0<=T, -infinity

 Title: Re: Jitter in Limiting Amplifier Post by Hans on Jul 28th, 2003, 2:55pm Let's see if I'm looking at this the right way. Your claim is that tdnoise is a purely discrete computation with a sampling rate equal to the PSS fundamental f0 (=1/T0). As such, the interval of interest would be [ f, f+f0] where f can be any value due to the periodic nature of the spectrum. Any effects due to aliasing would be included in this window and integration should yield a true picture of noise across all frequencies. Thinking about it this way, I would have to agree with an integration range from 0 to f0. If we were only to cover half that range, we would neglect the portion that occurs at negative frequencies (and also folded to the range f0/2 - f0). Although there is no "new" information in those ranges, signal power does appear in it. Am I making a wrong assumption in here?Thanks for your reply and putting this issue in a new perspective. I cretainly would appreciate it, if the Cadence manuals would go into more detail about their simulation tools - just specifying what needs to be done for a very specific example can lead to a false sense of confidence. How about some equations with the documentation?Anyway, I'll stop my rant about poor documentation. Thanks again for taking the time to reply to my post, Hans

 Title: Re: Jitter in Limiting Amplifier Post by pancho_hideboo on Jul 28th, 2003, 5:19pm > Thinking about it this way,> I would have to agree with an integration range from 0 to f0.> If we were only to cover half that range,> we would neglect the portion that occurs at negative frequencies> (and also folded to the range f0/2 - f0). :-/No, integration range has to be from 0 to PSSfund/2.Since PSD of Spectre is 1-sided view spectrumwhich is twice of 2-sideded view spectrum.For example, integration range is from 0 to fmaxfor normal noise analysis. This is because PSD is 1-sided view.Here you don't have to integrate from -fmax to +fmax.Cadence will revise TDnoise explanation in SpectreRF manual soon.You will see the reason why both analysis range andintegration range are from 0 to PSSfund/2.If you integrate from 0Hz to PSSfund,then you will include the same noise many times,so an integral range should be limited to 0Hz~PSSfund/2.About noise folding, see below.(3) Folding and Alias. When inputing noise into a linear time periodic varying (LTPV) system,because of frequency translation, the output noise at f has contributionfrom input noise at f+n*PSSfund (-infinity

Title: Re: Jitter in Limiting Amplifier
Post by jeffyan on Jun 25th, 2008, 5:10am

pancho_hideboo wrote on Jul 28th, 2003, 8:08am:
 Description about TDnoise in SpectreRF manual is wrong. :'(TDnoise setting has to be like following.(1) Sweep Range for Pnoise.This should be from 0 to PSSfund/2.Sweep Range is the one we fill in the PNoise analysis form. For regular pnoise(noisetype=source), the range could be from 0 to any frequency we want.For time-domain pnoise (noisetype=timedomain), the range should be from 0 to PSSfund/2.Time-domain noise PSD is periodic with PSSfund so PSD is symmetric around PSSfund/2. (2) Frequency Integration Range of PSD. This should be from 0 to PSSfund/2.For time-domain noise (noisetype=timedomain), SpectreRF calculates the PSD of the discrete (or sampled) noise at t0+n*T (T=1/PSSfund, 0<=t0<=T, -infinity

hi,
you mean this description on tdnoise is not right?
thanks

Title: Re: Jitter in Limiting Amplifier
Post by pancho_hideboo on Jun 25th, 2008, 8:15am

jeffyan wrote on Jun 25th, 2008, 5:10am:

pancho_hideboo wrote on Jul 28th, 2003, 8:08am:
 Description about TDnoise in SpectreRF manual is wrong. :'(TDnoise setting has to be like following.(1) Sweep Range for Pnoise.This should be from 0 to PSSfund/2.Sweep Range is the one we fill in the PNoise analysis form. For regular pnoise(noisetype=source), the range could be from 0 to any frequency we want.For time-domain pnoise (noisetype=timedomain), the range should be from 0 to PSSfund/2.Time-domain noise PSD is periodic with PSSfund so PSD is symmetric around PSSfund/2. (2) Frequency Integration Range of PSD. This should be from 0 to PSSfund/2.For time-domain noise (noisetype=timedomain), SpectreRF calculates the PSD of the discrete (or sampled) noise at t0+n*T (T=1/PSSfund, 0<=t0<=T, -infinity

hi,
you mean this description on tdnoise is not right?
thanks

No, content of "tdnoise.pdf" is right.

My post is matched to "tdnoise.pdf".
Is there any contradiction point in "tdnoise.pdf" ?

Title: Re: Jitter in Limiting Amplifier
Post by jeffyan on Jun 27th, 2008, 11:14pm

pancho_hideboo wrote on Jun 25th, 2008, 8:15am:

jeffyan wrote on Jun 25th, 2008, 5:10am:

pancho_hideboo wrote on Jul 28th, 2003, 8:08am:
 Description about TDnoise in SpectreRF manual is wrong. :'(TDnoise setting has to be like following.(1) Sweep Range for Pnoise.This should be from 0 to PSSfund/2.Sweep Range is the one we fill in the PNoise analysis form. For regular pnoise(noisetype=source), the range could be from 0 to any frequency we want.For time-domain pnoise (noisetype=timedomain), the range should be from 0 to PSSfund/2.Time-domain noise PSD is periodic with PSSfund so PSD is symmetric around PSSfund/2. (2) Frequency Integration Range of PSD. This should be from 0 to PSSfund/2.For time-domain noise (noisetype=timedomain), SpectreRF calculates the PSD of the discrete (or sampled) noise at t0+n*T (T=1/PSSfund, 0<=t0<=T, -infinity

hi,
you mean this description on tdnoise is not right?
thanks

No, content of "tdnoise.pdf" is right.

My post is matched to "tdnoise.pdf".
Is there any contradiction point in "tdnoise.pdf" ?

hi,
could you tell me why integral frequency range is 0 to PSSfund/2, instead of 0 to infinte in discrete freq domain?

Title: Re: Jitter in Limiting Amplifier
Post by pancho_hideboo on Jun 28th, 2008, 12:14am

jeffyan wrote on Jun 27th, 2008, 11:14pm:
 could you tell me why integral frequency range is 0 to PSSfund/2, instead of 0 to infinte in discrete freq domain?

Rather why do you integrate 0 to infinite ?

See the following.
http://www.designers-guide.org/Forum/YaBB.pl?num=1207830622

I've been very disgusted about explaining tdnoise.
It seems people whose name is  "****yan" has same question.

 Title: Re: Jitter in Limiting Amplifier Post by jeffyan on Jun 28th, 2008, 1:54am hi,thanks,it seem that you stated the truth, but you didn't give the reason.the integral power is infinite if the range is from 0 to infinite, and if integrated from 0 to fsample/2, the noise power is identical to the original one.

Title: Re: Jitter in Limiting Amplifier
Post by pancho_hideboo on Jun 28th, 2008, 3:38am

jeffyan wrote on Jun 28th, 2008, 1:54am:
 it seem that you stated the truth, but you didn't give the reason.

I gave enough reason which you can understand if you have basic mathematical or signal processing theory back ground.

"Sampling Theory", "Impulse Sampling", "Energy", "Repeated Spectrum Replica"
You should read the following again with considering the above issues.

http://www.designers-guide.org/Forum/YaBB.pl?num=1207830622

jeffyan wrote on Jun 28th, 2008, 1:54am:
 the integral power is infinite if the range is from 0 to infinite, and if integrated from 0 to fsample/2, the noise power is identical to the original one.

Correct.