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A/D source impedance

Rajinder

Jan 30, 2016
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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,
Raj
 

Harald Kapp

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Nov 17, 2011
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The PIC datasheet states that it has a source impedance of 10K.
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?
Does this mean, I need to drive it with something that is lower in value so that it won't load the signal.
Definitely yes. It is common to use an opamp to directly drive th input of any ADC to avoid this effect (and others).
 

BobK

Jan 5, 2010
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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).

Bob
 
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