Utilizing multiple ADCs on one channel for high sample rate.

[nargetdev]

Hello everybody,

I searched the forums and saw numerous questions regarding sampling multiple ADCs but none for this exact use case.

The question is simple - is it possible to sample one channel of analog output using multiple ADCs and high-z selectors/enable (are the selectors even necessary?) to cycle through the 6 ADCs and produce 6 times the sampling frequency of a single ADC?

I'm assuming this will be an incredibly timing intensive problem (allow time for each ADC capacitor to respond). I haven't tried to implement this because I think there are two many variables I simply don't have knowledge of - and perhaps it's not be possible.

Thank you!

[Stefan Birnir Sverrisson]

Hi nargetdev

What is your requirement exactly? What sampling frequency do you need? How accurate do you need the sampling to be Do you intend to use the softdevice? 6 ADCs, you mean 6xnRF51s? Can you explain your use case and requirement in more detail?

[nargetdev]

I mean to say that I want to use a single nRF51822 to sample in sequence on each internal ADC netting a higher sample frequency. I do not know some basic facts like whether there actually are 6 ADCs inside or just 6 routs to the same ADC.

[Stefan Birnir Sverrisson]

Hi nargetdev

Thank you for your clarification.

The nRF51 has a single ADC. It can be used however to sample on multiple pins sequentially. There is an interrupt driven ADC example here that samples on two input pins sequentially, but it can be modified to sample on more number of analog input pins.

The maximum sampling frequency is dependent on what resolution you choose for the ADC and if you use softdevice (BLE) or not.

• 8-bit sampling takes 20us, so if you do not use the softdevice you can obtain 50 kHz sampling frequency.
• 10 bit sampling takes 68us, so you can obtain 14,7 kHz sampling fequency without using softdevice.
• If you use softdevice and have 3rd revision nRF51, you can obtain sampling frequency approximately 2-8 kHz, depending on how much data you send over the air.