+ Post New Thread
Results 1 to 5 of 5
  1. #1
    Advanced Member level 1
    Points: 2,500, Level: 11

    Join Date
    Feb 2016
    Posts
    459
    Helped
    1 / 1
    Points
    2,500
    Level
    11

    Use of comparator for sampling repetitive waveforms

    A comparator can replace ADC to capture only repetitive waveforms

    Could anyone explain how does comparator serve this purpose ?

    •   AltAdvertisment

        
       

  2. #2
    Super Moderator
    Points: 70,685, Level: 64
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster 3rd Helpful Member

    Join Date
    Apr 2014
    Posts
    14,465
    Helped
    3292 / 3292
    Points
    70,685
    Level
    64

    Re: Use of comparator for sampling repetitive waveforms

    Hi,

    I can´t find this statement in the attached document.

    Please refer to the source of this statement.

    But generally
    * any comparator is an 1 bit ADC.
    * You may modify the threshold_level to get the timing of this level..

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.


    1 members found this post helpful.

    •   AltAdvertisment

        
       

  3. #3
    Advanced Member level 1
    Points: 2,500, Level: 11

    Join Date
    Feb 2016
    Posts
    459
    Helped
    1 / 1
    Points
    2,500
    Level
    11

    Re: Use of comparator for sampling repetitive waveforms

    Someone explained me the following :

    imagine the waveform as a bitmap image, one pixel per sample

    a DAC driving the inverting input of the comparator sets your Y coordinate
    adjusting the phase of your sampling clock relative to the waveform sets your X coordinate

    take a few thousand samples at each pixel to get an intensity-graded image
    this directly measured the cumulative distribution function of the waveform - the probability the voltage is

    the partial derivative wrt dV is the probability density function,
    the probability the voltage is =V at that time which is your final eye pattern
    Anyone got what he means ?
    Last edited by promach; 12th March 2019 at 09:04.



    •   AltAdvertisment

        
       

  4. #4
    Super Moderator
    Points: 77,322, Level: 67
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    12,659
    Helped
    4222 / 4222
    Points
    77,322
    Level
    67

    Re: Use of comparator for sampling repetitive waveforms

    a DAC driving the inverting input of the comparator sets your Y coordinate
    The clue is in that line.

    A DAC produces a voltage which is then compared to the sample using a simple comparator, the output tells you whether the sample is above or below the DAC output. You then repeat the process with a different DAC voltage (intelligently selecting higher or lower) and compare again. When the comparator output changes you know the voltage programmed into the DAC is the same as or very close to the sample voltage. You know what the DAC was programmed to produce. It's called successive approximation because each new trial brings you closer to knowing the sample voltage.

    take a few thousand samples at each pixel to get an intensity-graded image
    this directly measured the cumulative distribution function of the waveform - the probability the voltage is
    the implication being that if you do the above repeatedly and fast enough, you sample the shape of the waveform.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


    1 members found this post helpful.

  5. #5
    Advanced Member level 1
    Points: 2,500, Level: 11

    Join Date
    Feb 2016
    Posts
    459
    Helped
    1 / 1
    Points
    2,500
    Level
    11

    Re: Use of comparator for sampling repetitive waveforms

    if you do the above repeatedly and fast enough, you sample the shape of the waveform.
    But can 1-bit ADC (comparator) do this ? Why does comparator only works for sampling repetitive waveforms ?



--[[ ]]--