ICL7107 Accuracy issue

Discussion in 'The Projects Forum' started by Mohanavijay, Dec 28, 2017.

  1. Mohanavijay

    Thread Starter New Member

    Sep 6, 2014
    1
    0
    Hi,

    I am currently working on verifying ICL7107. I am following circuit as given in the datasheet for 200mV range. Output on the display is not accurate. When I give 112.1mV to in put, display is not stable and microvolt display keeps swinging like 1120, 1121, 1123 1122.
    Also when I try to capture the digits and display in screen, i need min of 400~600mS delay time after I give input and capture the display. Is there any suggestion to reduce delay time & to get accurate measure.

    Regards,
    VJ
     
  2. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    7,701
    2,167
    I know what a 7107 is, but many people don't.
    Please post the datasheet and any app notes.
    Please post your schematic.
    What do you mean by "verifying"?

    ak
     
  3. MrChips

    Moderator

    Oct 2, 2009
    18,374
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    You also need to post photos of your board. Many performance issues can be related to actual board layout and construction.
     
  4. Raymond Genovese

    Well-Known Member

    Mar 5, 2016
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    It looks like the circuit may be working fine, but you have an issue with the decimal point. IOW 112.1 mv in might reasonably be expect to bounce around between 112.0-112.3 or on your display (1120-1123). Have you looked carefully at Fig 6 in the data sheet, for example?
     
  5. wayneh

    Expert

    Sep 9, 2010
    16,024
    6,119
    You also need to consider the accuracy of whatever you are using to "verify" the IC. It may be more accurate than your test instruments and methods. And when you are done you will have only sampled one chip, not the population.
     
  6. MrChips

    Moderator

    Oct 2, 2009
    18,374
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    What is your ADC clock frequency?

    ICL7107 is an integrating ADC. For optimum performance, you want to select the ADC clock frequency to reject AC mains noise pickup.

    ADC clock frequency of 40kHz will reject both 50Hz and 60Hz AC mains pickup. This will give you a sampling rate of 2.5 readings per second (or 400ms period).

    For faster conversion speeds, choose 200kHz oscillator frequency for 50Hz rejection and 12.5 conversions per second (or 80ms period).
     
  7. bertus

    Administrator

    Apr 5, 2008
    19,426
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    Hello,

    The following application note might also give you some tips.

    Bertus
     
  8. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    What are you using for the integrator cap?
     
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