Stats

  • Locked Locked
  • Replies 9
  • Subscribers 125
  • Views 17177
  • Members are here 0
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Could anyone explain this sampled noise simulation result

SpiceMonkey

Hi, I'm learning sampled circuit noise simulaton, pss+pnoise, start with the simplest S/H circuit.

- Simulator, Spectre 19.1

- TestBench (fig1), a switch-capacitor S/H circuit, fs 400KHz >> f(RC-EBW) 27KHz, no alising should happen. (r=920K, c=10p)

- Pnoise Setup (fig2), sampled noise, sampled phase, 2 outputs with Vc and Vn2

- Results (fig3). For density, Vc is twice larger than Vn2; while for EBW, Vn2 is twice larger than Vc.

Though the total noise of Vc and Vn2 are same, but the bandwidth and density are different.

I think Vn2 is more reasonable, the densisty and bandwidth are exactly what I calculate, but how to explain Vc? Could anyone help? thank you!

Pnoise

Parents

  • From Tutorial of Noise Analysis in Switched-Capacitor Circuits, page 37, I reprodece the same results in Matlab.

    Fullscreen 8156.SH_noise.txt Download 
    clc;clear;
fs=400e3;R=920e3;C=10e-12;T=300;K=1.38e-23;duty=0.5;
N=duty/fs/(R*C);
syms f;
X(f)=2/fs * K*T/C * (1-exp(-2*N)) / (1-2*exp(-N)*cos(2*pi*f/fs)+exp(-2*N));
fplot(X(f),[1,10*fs/2])
set(gca,'xscale','log')

    If possible, is anyone could explain this "intuition", page 32

    - RC<0.5/fs, little correlation, whilte spectrum;

    - RC>0.5/fs, significant correlation, colored spectrum.

  • in reply to SpiceMonkey

    Dear SpiceMonkey,,

    It appears the document you are referring to is not a Cadence publication. Nevertheless, I did examine the document and specifically page 32. The author shows exactly what is meant by "correlation" graphically on the author's following two pages (33 and 34). For small RC time constants with respect to the sample period, each sample of the noise is not well correlated to the prior sample or following sample since the RC time constant settling occurs very quickly relative to the switching period. However, if the RC time constant is large with respect to the sample period (the author chose a ratio of 1 to shown on page 34), then the relatively long RC settling will prevent the prior sample, present sample, and following sample from varying significantly from one another. Hence, there is a high degree of correlation between the three samples. Contrast this to the example on page 33 where the ratio of sampling period to the RC time constant is 10. The settling time in this case does allow the prior, present and following samples to differ significantly from each other and hence they are not as well correlated.

    Does this help SpiceMonkey?

    Shawn

Reply
  • in reply to SpiceMonkey

    Dear SpiceMonkey,,

    It appears the document you are referring to is not a Cadence publication. Nevertheless, I did examine the document and specifically page 32. The author shows exactly what is meant by "correlation" graphically on the author's following two pages (33 and 34). For small RC time constants with respect to the sample period, each sample of the noise is not well correlated to the prior sample or following sample since the RC time constant settling occurs very quickly relative to the switching period. However, if the RC time constant is large with respect to the sample period (the author chose a ratio of 1 to shown on page 34), then the relatively long RC settling will prevent the prior sample, present sample, and following sample from varying significantly from one another. Hence, there is a high degree of correlation between the three samples. Contrast this to the example on page 33 where the ratio of sampling period to the RC time constant is 10. The settling time in this case does allow the prior, present and following samples to differ significantly from each other and hence they are not as well correlated.

    Does this help SpiceMonkey?

    Shawn

Children

Community Guidelines

The Cadence Design Communities support Cadence users and technologists interacting to exchange ideas, news, technical information, and best practices to solve problems and get the most from Cadence technology. The community is open to everyone, and to provide the most value, we require participants to follow our Community Guidelines that facilitate a quality exchange of ideas and information. By accessing, contributing, using or downloading any materials from the site, you agree to be bound by the full Community Guidelines.