>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>Sent: 15 December 2005 14:53
>To: piclist@mit.edu
>Subject: [PIC]correct info about op drive of pic ADC
>
>
>weeks ago from pic list, I got information about drive
>pic adc. After one week test, consummed 
>several proto pcb, burning/used small pile of 
>components, I found perfect solution:
>
>Simple R net divider: 3651+ 3650 to 1301.
>I get 0.1% accuracy and 20.46 V reading as
>1023 in software, totally rounded. So, 
>when do real number calculation, you don't 
>have the last digit rolling arround.
>
>Talk about add an op powered divider, it has 
>no much value, due to bring noise. Second,
>pic itself is cmos, 100p adc, 10K source Z is 
>already very kindly specification. 

The 10K is specified not because of general CMOS input imepdance, but because the input of the ADC has a leakage current (which is of course temperature dependant).  To achieve the specified accuracy over the full voltage/temperature range the source impedance requirements have to be met.  If acheiving the full accuracy is not important, then obviously a higher impedance may be used.

Regards

Mike

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