ADC sampling rate with oversampling issue

RE: ADC sampling rate with oversampling issue

jawadk — Mon, 09 Nov 2020 13:17:59 GMT

Hi,

Ok thank you for your help

Best Regards

RE: ADC sampling rate with oversampling issue

Karl Ylvisaker — Mon, 09 Nov 2020 11:36:02 GMT

Hello again JK,

[quote user="jawadk"]

the calculation isn't seem right for me

When I sampled in 2000Sps with 32 oversampling it succeeded !, but the calculation is (2^32)*2000 = 8589934592000 Sps. this is way bigger than 200KSps.

What I am missing here !?

[/quote]

Please see the overview of the Oversampling register and register that I referenced you in my previous comment - there is no way for you to configure 2^32 oversampling - that would indeed be way too big, and frankly not very useful.
Instead, you will be configuring 2^5, to achieve 32 oversampling - as detailed in the documentation.

Please do not hesitate to ask if anything still should be unclear! :)

Best regards,
Karl

RE: ADC sampling rate with oversampling issue

jawadk — Mon, 09 Nov 2020 09:49:51 GMT

Hi,

Last question:

the calculation isn't seem right for me

When I sampled in 2000Sps with 32 oversampling it succeeded !, but the calculation is (2^32)*2000 = 8589934592000 Sps. this is way bigger than 200KSps.

What I am missing here !?

Thank you for your help

Best Regards

RE: ADC sampling rate with oversampling issue

Karl Ylvisaker — Mon, 09 Nov 2020 09:24:36 GMT

Hello again JK.

[quote user="jawadk"]The Acquisition time is NRF_SAADC_ACQTIME_10US.[/quote]

That explains why you saw the sampling results that you posted about originally then.
To be able to achieve 200 kHz sampling, you will need to use the 3 US ACQTIME. With 10 Us, you can expect to see exactly the results you posted in your original ticket.

Best regards,
Karl

RE: ADC sampling rate with oversampling issue

jawadk — Mon, 09 Nov 2020 08:59:49 GMT

Hi,

Thanks for your reply.

The Acquisition time is NRF_SAADC_ACQTIME_10US.

Best Reagrds

RE: ADC sampling rate with oversampling issue

Karl Ylvisaker — Mon, 09 Nov 2020 08:52:26 GMT

Hello JK,

[quote user="jawadk"]

The Samples that the ADC sample is 2^oversampling number ? and not just the oversampling numer.

For example if the oversampling is 2, so the actual samples number the ADC sample is 2^2 = 4 yes ?

[/quote]

Yes, this is correct - you can read more about this in the SAADC peripheral documentation, specifically looking at the Oversampling section, and the Oversampling register.

Did you check which Acquisition time you used during your testing?

Best regards,
Karl

RE: ADC sampling rate with oversampling issue

jawadk — Sun, 08 Nov 2020 08:55:53 GMT

Hi,

Thank you for your reply.

The Samples that the ADC sample is 2^oversampling number ? and not just the oversampling numer.

For example if the oversampling is 2, so the actual samples number the ADC sample is 2^2 = 4 yes ?

RE: ADC sampling rate with oversampling issue

Karl Ylvisaker — Tue, 03 Nov 2020 12:58:43 GMT

Hello JK,

[quote user=""]I am using the nRF5SDK160098a08e2 for that and based on the saadc example.[/quote]

What changes did you make to the example? Did you modify the channel / SAADC configurations? - if so, how have you modified them?

The SAADC example uses the default SAADC and channel configurations for Single ended inputs - which is configured to 10 µs Acquisition time. Did you change this?

Looking forward to resolving this issue together!

Best regards,
Karl