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 How do you simulate the input referred noise for a chopper amplifier? 

Last post Fri, Jun 10 2011 8:04 AM by BenMartin. 4 replies.
Started by harmonics 29 May 2011 12:36 PM. Topic has 4 replies and 3573 views
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  • Sun, May 29 2011 12:36 PM

    • harmonics
    • Not Ranked
    • Joined on Sat, May 21 2011
    • London, London
    • Posts 2
    • Points 55
    How do you simulate the input referred noise for a chopper amplifier? Reply

    Hi,

    trying to simulate a chopper amplifier. For testing it is configured as a voltage follower. There is only one clock all the non overlapping clocks ect are derived from it. The problem is that the flicker noise is not being reduced on the input noise plot when I use the following pnoise, pss settings:


    pss  pss  fund=100k  harms=3  errpreset=conservative
    +    annotate=status
    pnoise  (  out  0  )  pnoise  sweeptype=relative  relharmnum=1
    +       start=1  stop=50k  log=20  maxsideband=20  iprobe=V2  refsideband=0
    +       annotate=status

    I have tried various settings and cannot reduce the flicker noise. I have verified that the chopper is working and it does remove the dc offset when inserting a non zero vdc at the inputs in the time simulation. I have also tried following the chopper opamp with a with a sample and hold and taking the output for pnoise simulation from the sample and hold but this still does not reduce the flicker noise seen on the direct plot.

    I've read Ken Kundert's sc-filters.pdf from www.designers-guide.org/Analysis/  and have successfully used pss and pnoise to simulate an oscillator in the past following the spectreRF tutorial.

    There has been a few posts on this site as well as others but the only advise given is to eternally point people to Ken Kundert's sc-filters.pdf or the cadence manual.

    Any ideas where I'm going wrong with the simulation setup?

    Regards,

    harmonics 

    • Post Points: 20
  • Thu, Jun 9 2011 10:56 PM

    • BenMartin
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    • Joined on Fri, Dec 17 2010
    • Posts 3
    • Points 30
    Re: How do you simulate the input referred noise for a chopper amplifier? Reply
    I have the same question. I don't see 1/f noise being modulated away from the origin. Did you ever figure it out? Ben
    • Post Points: 20
  • Fri, Jun 10 2011 3:55 AM

    • harmonics
    • Not Ranked
    • Joined on Sat, May 21 2011
    • London, London
    • Posts 2
    • Points 55
    Re: How do you simulate the input referred noise for a chopper amplifier? Reply

    BenMartin:
    I have the same question. I don't see 1/f noise being modulated away from the origin. Did you ever figure it out? Ben

    It should be set to the zero harmonic ie relharmnum=0 not relharmnum=1 as that starts the sweep around the clock (see my original spectre settings above) which was not the intention. After that the settings are fine and the chopper works as desired regarding 1/f noise.

    The error was obvious but no thanks to this forum though.

    • Post Points: 35
  • Fri, Jun 10 2011 5:30 AM

    Re: How do you simulate the input referred noise for a chopper amplifier? Reply

    Sorry, been rather busy over the last few weeks and did not have a chance to read this through carefully and spot the error. Unfortunately the symptoms weren't that clear, but you're right - it's an obvious mistake, since the input and output frequency of the amplifier are the same.

    Regards,

    Andrew.

    • Post Points: 5
  • Fri, Jun 10 2011 8:04 AM

    • BenMartin
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    • Joined on Fri, Dec 17 2010
    • Posts 3
    • Points 30
    Re: How do you simulate the input referred noise for a chopper amplifier? Reply
    Thank you!
    • Post Points: 5
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Started by harmonics at 29 May 2011 12:36 PM. Topic has 4 replies.