nRF52840 SAADC Input Stage

[ThePinkPanther]

Hi,

We are using the nRF52840 SoC.

1. The following image is taken from the datasheet:

It shows a Gain block before the SAR core

a. Does the Gain block serve also as a buffer?

b. What is the Gain BW?

 

1. The following image describes a simplified SAADC sample network:

- Does the Rsource external to the nRF52840 SoC?

 

Thank you

[Jørgen Holmefjord]

Hi,

Does the Gain block serve also as a buffer?

This is a simplified block diagram. There are input buffers between the MUX and the SAR core.

What is the Gain BW?

I'm not sure we have any parameters for this. Can you elaborate more on what you are looking for?

Does the Rsource external to the nRF52840 SoC?

Yes, this is the external source resistance.

Best regards,
Jørgen

[ThePinkPanther]

Thanks,

We’re trying to understand the bandwidth requirement of an external amplifier, which is connected to the nRF52840 SoC and driving the ADC. 

This external amplifier should have the ability to load the sample and hold capacitor in the SAADC fast enough, in order to withstand a certain sample rate/acquisition time - while maintaining the gain it supposes to provide. This ability is referred, per my question, as Gain BW. If the internal Gain buffers, between the MUX and the SAADC, have adequate Gain BW, we can relax the requirement in this aspect from the external amplifier in our application.  

Are there are any other recommendations on how to drive the SAADC input, besides the acquisition time configuration per Rsource?