ADC Sample Time

[brianforde9]

Posted on October 30, 2008 at 15:26

ADC Sample Time

#adc-sampling-rate

[brianforde9]

Posted on May 17, 2011 at 12:50

What effect does ADC Sample Time have on the ''quality'' of the measured voltage? Why adjust this value?

Thanks in advance...

Brian F.

[brianforde9]

Posted on May 17, 2011 at 12:50

Quote:

On 30-10-2008 at 17:11, Anonymous wrote:

There are some giudelines for selecting the sampling time in the ADC part of the device datasheets.

Thanks, but I can't find any such. There is an indication as to how to calculate conversion time, given a sample time, but nothing to determine what the sample time should be. Does anyone know what size the sampling capacitor is? In any case, changing the sample time appears to have no effect on my measured value...

Regards,

Brian F.

[obtronix]

Posted on May 17, 2011 at 12:50

Depending on the external resistance you have to wait for the sampling cap to charge up (simple RC time constant) if you don't wait long enough you will read the wrong value.

[ivanov-i]

Posted on May 17, 2011 at 12:50

It is the time for charging the sampling capacitor trough the external source impedance. The internal switch resistance is also included in the calculation.

There are some giudelines for selecting the sampling time in the ADC part of the device datasheets.

[brianforde9]

Posted on May 17, 2011 at 12:50

My bad. Found the value...

12pF

Brian F.

[amoore]

Posted on January 04, 2014 at 01:03

AN2834 (How to get the best ADC accuracy in STM32Fx...) covers in detail the effect on conversion error of the sampling time, source resistance, and internal ADC capacitance.