Reading SAADC signals that are in the range of 10- 100μV in the sampling frequency of 1kHz

[Lydia_Cho]

Hello all, 

I have trouble reading saadc data with an amplitude of 10 µV - 100 µV with a sampling rate of 1K Hz by using nrf52832. I was wondering if I could get advice/help to solve this issue. 

From my understanding, I need to lower the reference voltage to read low voltage. Two options I tried (please correct me if I did it incorrectly) 

1. change VDD 

I assumed sample = 10 for 10 µV, a gain of 1/4

To solve for VDD : 10 * [VDD/4] * [1/gain] / (2^12) = 10µV. VDD = 0.001. Since the VDD is too low, it did not work. 

( I could change the gain to 4, but still too low)

2. change the resolution to 2^14 and gain = 4 using internal voltage (0.6)

It did not read data properly

Questions

- Do I need to change from the hardware to read low amplitude? Is it not possible to read these signals just by using nrf52832?

- Is it possible to read data with the frequency of 10kHz using nrf52832?

I would appreciate any help to solve this issue. 

 

[haakonsh]

The SAADC cannot resolve that signal as its amplitude is far too low, the signal will be buried in offset and noise. 

What you need is an instrumental amplifier that boosts the signal to a more appropriate level for the SAADC. 

The SAADC can handle up to 200ksps at 3µs acquisition time.