ADC internal resistance

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muhammad saad malik
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Joined: Wed Dec 16, 2015 4:52 am

ADC internal resistance

Post by muhammad saad malik » Wed Dec 16, 2015 5:02 am

i am working on arm cortex m tm4c123h6pm microcontroller. i am measuring voltage using an ADC. i need to design a voltage divider to measure voltage and for that i need to consider the ADC's internal resistance as well. i checked out its value in the datasheet but i don't know whether it is in parallel or series with the pin? plz help

dschlic1
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Joined: Thu Apr 17, 2008 7:58 am

Re: ADC internal resistance

Post by dschlic1 » Wed Dec 23, 2015 9:56 am

Most ADCs have a dynamic input impedance: They charge a capacitor in a sample and hold function. Better place an op-amp buffer between the divider and the ADC input.

jremington
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Location: Eugene, Or

Re: ADC internal resistance

Post by jremington » Wed Dec 23, 2015 10:36 am

The data sheet should tell you the maximum recommended source impedance, which you can use as a guideline.
The impedance of a voltage divider is the parallel combination of the two resistors.

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