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A/D source impedance

Discussion in 'General Electronics Discussion' started by Rajinder, Nov 26, 2017.

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  1. Rajinder


    Jan 30, 2016
    Hi all,
    I am looking to do some A/D measurements with a PIC microcontroller.
    The PIC datasheet states that it has a source impedance of 10K.
    Does this mean, I need to drive it with something that is lower in value so that it won't load the signal. I have a voltage divider connected to this pin (2 X 10K), the middle connection going to the a/d of the PIC. Any help would be appreciated.
    Best regards,
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Which datasheet? I doubt that the A/D's input is defined with a source impedance. SOurce impedance would be given for a power source, but not for a load. You probably mean input impedance?
    Definitely yes. It is common to use an opamp to directly drive th input of any ADC to avoid this effect (and others).
  3. BobK


    Jan 5, 2010
    I am looking a the datasheet for the PIC12F1840.

    What the datasheet says is that the "recommended impedance of analog voltage source" is 10K. This means that the voltage source driving the pin that you are trying to read with the ADC should have an impedance of no more than 10K. (less is better).

    Harald Kapp likes this.
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