Gain vs ADC performance vs ADC settling time

[veerubiji]

Hi all,

I have some basic doubts in ADC conversion. I am using AD7798 ADC. I am reading ADC values using AT90USB1287 micro controller using SPI communication. I am able to read ADC values perfectly but i have some doubts.

I had gone through the datasheet several times. I am setting Configuration register as "0x0230" and mode register as "0x0009". It means update rate as 16.7Hz and gain from "4 to 128".

When i try to read ADC value with 16.7Hz update rate it is taking more time but accurate values.

I would like to get values more fast than present time so i changed update rate from 16.7 Hz to 232Hz. Now ADC reading values more faster but not accurate.

How can i read ADC values more accurate and faster? Changing gain will effect ADC update rate?

Could anyone give me some explanation regarding Gain Vs Update rate vs accuracy?

From the datasheet i see that gain will effect on resolution and update rate will effect on signal to noise ration.
**broken link removed**

 

[FvM]

Changing gain will effect ADC update rate?

No, PGA gain and update rate are indepent settings.

Both ADC and PGA incorporate noise sources, by varying the update rate and gain, the output noise level will be changed. The relation between update rate and noise is primarly a matter of different noise bandwidth, in addition the specific noise-shaping characteristic of delta-sigma converters involves an overproportional increase above a certain sampling rate.

Discussing the noise proporties of a particular ADC isn't very meaningful without considering the signal properties, however.

 

[veerubiji]

No, PGA gain and update rate are indepent settings.

Both ADC and PGA incorporate noise sources, by varying the update rate and gain, the output noise level will be changed. The relation between update rate and noise is primarly a matter of different noise bandwidth, in addition the specific noise-shaping characteristic of delta-sigma converters involves an overproportional increase above a certain sampling rate.

Discussing the noise proporties of a particular ADC isn't very meaningful without considering the signal properties, however.

Thanks for your explanation.....