The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Simulators >> Circuit Simulators >> How to see the Noise Power output in SpectreRF?
https://designers-guide.org/forum/YaBB.pl?num=1046683537

Message started by sch on Mar 3^rd, 2003, 1:25am

Title: How to see the Noise Power output in SpectreRF?
Post by sch on Mar 3^rd, 2003, 1:25am

I run the simple sample and hold circuit by pss and pnoise command in Spectre, but cannot see the noise output power vs. frequency , why? How to see it in Spectre?

Title: Re: How to see the Noise Power output in SpectreRF
Post by Jitter Man on Mar 3^rd, 2003, 7:46am

To compute the noise of a sample and hold, you would apply a periodic clock and run a PSS analysis to find the periodic operating point, then run a PNoise analysis to compute the output noise. I sounds like this is what you did, but you claim that you cannot see the output noise. I'm not sure I know what this means. Is it that you do not know how to plot the output noise, or is it that when you plot the noise you find it to be zero? If it is the latter, please describe your sample-and-hold circuit. Is it constructed from transistors, or is it a behavioral model?

[glb]Jitter Man[/glb]

Title: Re: How to see the Noise Power output in SpectreRF
Post by sch on Mar 3^rd, 2003, 11:14pm

I run the simple RC circuit, replaced the R by switch cap. and see
the output in spectre, but I want to see the equivalent noise power 4.11n or noise voltage 64uV , the capacitor is 1p. how to do the post -processing??

Title: Re: How to see the Noise Power output in SpectreRF
Post by Jitter Man on Mar 4^th, 2003, 2:57pm

Once you run the PNoise analysis, you can use Results->Print->Noise Summary to calculate the total integrated noise. Be sure to select integrated noise. You may have to scroll down to see the total output noise.

You will probably want to take some steps to assure that the noise you measure is the noise you want. In particular, you probably only want the noise present when the output has settled, and not when the output is still settling or the noise during the inactive phase. This is most easily accomplised by using the time-domain noise feature (Noise Type = timedomain) on the PNoise form.

[glb]Jitter Man[/glb]

Title: Re: How to see the Noise Power output in SpectreRF
Post by sch on Mar 6^th, 2003, 6:31pm

If I run a sample and hold circuit in transistor level,what type signal I should feed to the input of S/H?If I can see the noise
power only by PSS and PNOISE command to see the noise power? I do't want to use time domain analysis, it spend much time.

Title: Re: How to see the Noise Power output in SpectreRF
Post by Jitter Man on Mar 6^th, 2003, 7:32pm

The input signal should be turned off (it should be constant valued), but you must apply the clock. Perform the PSS analysis with only the clock applied, with the period of the PSS analysis matching that of the clock period.

Then perform the PNoise analysis.

[glb]Jitter Man[/glb]

Title: Re: How to see the Noise Power output in SpectreRF
Post by sch on Mar 6^th, 2003, 11:49pm

The S/H circuit has sinx/x function problem, so I have to put
a ZOH circuit at the output of S/H , right? When calculate the
power spectral density of S/H I have to divide the sinx/x ,right?
and then integral the noise power density to the half of sampling clock frequency,right?, Then I will get the total noise power. But if all of the above is right, I get the wrong noise power, why?

Title: Re: How to see the Noise Power output in SpectreRF
Post by Jitter Man on Mar 8^th, 2003, 12:44am

You are simulating a periodically clocked sample-and-hold, so you will see a sin(x)/x transfer characteristic. However, when computing total noise, it is generally not necessary to follow the sample-and-hold with another sampler (ZOH). The power in the hold mode noise generally dominates over the power in the track mode noise. If you are looking to compute the noise in the discrete-time output signal (as opposed to the continuous time signal that is output by default by SpectreRF), you should instead use the time-domain noise feature (noisetype=timedomain). That way you do not have to normalize out the sin(x)/x variations. Once you have the noise in the discrete time sequence (the time-domain noise), then you integrate from 0 to half of the clock frequency to calculate total noise.

[glb]Jitter Man[/glb]

Title: Re: How to see the Noise Power output in SpectreRF
Post by sch on Mar 13^th, 2003, 2:47am

How to deal with the S/H differential output, need to change them to single-end? Could I set the differential output directly to PNOISE command ? Did I have to specify the output node
to PSS command? ( If the noisetype=timedomain )

Title: Re: How to see the Noise Power output in SpectreRF
Post by Jitter Man on Mar 13^th, 2003, 8:22am

SpectreRF's PNoise analysis reports on the differential noise if you specify the output to PNoise using two nodes.

You do not need to specify the output nodes to the PSS analysis. You specify nodes to the PSS analysis only when simulating oscillators.

How you specify the output to the PNoise analysis is unaffected by the noisetype parameter.

[glb]Jitter Man[/glb]

Title: Re: How to see the Noise Power output in SpectreRF
Post by Ken Kundert on Mar 17^th, 2003, 1:01am

I have just added a new document to the website that discusses the process of using SpectreRF to predict the noise of switched-capacitor filters. You can find it at http://www.designers-guide.com/Analysis/.

-Ken