Analog ground on nrf52832 chip

[Piyush]

Hi, I am designing a PCB which consists of an analog circuitry (microphone + analog front end) and the nrf52832 chip. I am using inbuilt-ADC of this chip to sample the acoustic signal. The problem is that the PCB outputs a lot of noise than the expected one (from the simulations). Going through the literature, the suggestions for a PCB layout are that the ADC ground should be connected to analog ground. Also, the analog and digital power and ground supplies should be kept separate which is already taken care of in the design.

Which of the pin of nrf52832 is AGND? What other technique can help in reducing the noise to a minimal level? Please note that I am using Bluetooth for a wireless transmission of the data .

Thanks!

[Jørgen Holmefjord]

Hi,

There is no dedicated analog ground on the nRF52832. You can see all pins and their functionality on this page. Note this comment from the SAADC documentation:

The assumption in single-ended mode is that the internal ground of the ADC is the same as the external ground that the measured voltage is referred to. The ADC is thus sensitive to ground bounce on the PCB in single-ended mode. If this is a concern we recommend using differential measurement.

If you are using single ended mode, you can try switching to differential measurement. Another method to reduce noise is to enable oversampling.

Best regards,

Jørgen