SX9331 datasheet(11/48 Pages) SEMTECH

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SX9331

Final Datasheet

April 21, 2023

www.semtech.com

11 of 48

Rev. 2

Proprietary & Confidential

Semtech

3. Proximity Sensing Interface

3.1. Introduction

The purpose of the proximity sensing interface is to detect when a conductive object (usually a body part i.e. finger,

palm, face, etc.) is in the proximity of the system. Note that proximity sensing can be done through the air or through a

solid (typically plastic) overlay (also called “touch” sensing).

The chip’s proximity sensing interface is based on capacitive sensing technology. An overview is given the in figure

below.

Shield

Sensor

Analog

Front-End

(AFE)

Digital

Processing

SX9331

PROXSTAT

Finger, palm,

face, lap, etc

CSIOx

Figure 4: Proximity Sensing Interface Overview



The sensor can be a simple copper area on a PCB or FPC for example. Its capacitance (to ground) will vary

when a conductive object is moving in its proximity.



The optional shield can also be a simple copper area on a PCB or FPC below/under/around the sensor. It is

used to protect the sensor against potential surrounding noise sources and improve its global performance. It

also brings directivity to the sensing, for example sensing objects approaching from top only.



The analog front-end (AFE) performs the raw sensor’s capacitance measurement and converts it into a digital

value. It also controls the shield.



The digital processing block computes the raw capacitance measurement from the AFE and extracts a binary

information PROXSTAT corresponding to the proximity status, i.e. object is “Far” or “Close”. It also triggers AFE

operations (compensation, etc).

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