AN4038 datasheet(19/39 Pages) STMICROELECTRONICS

Part #	AN4038

Description	Guidelines to optimize proximity detection with STM8TL5xxx capacitive sensors

PDF	39 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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19 / 39 page

AN4038

Proximity sensor design

Doc ID 022686 Rev 1

19/39

4.1

Tx/Rx electrode spacing influence

The spacing between the Tx/Rx plates significantly impacts the detection distance. The

Tx/Rx electrode spacing also directly influences the projected capacitance and its area field.

Theoretically, increasing the spacing between the two electrodes influences the projected

capacitance and causes two important effects:

●

It increases the projected capacitance field area and decreases the projected

capacitance value. In this case, the influence induced by the hand or finger on the

projected capacitance value is higher. The sensitivity of the sensor is improved and

consequently the detection distance and area is increased.

●

It also increases the noise on the acquisition signal. The lower the projected

capacitance is, the higher the noise is.

Figure 16 shows the influence of the electrode spacing on the detection distance.

Figure 16.

Detection distance versus Tx/Rx electrode spacing

The closer the Tx/Rx electrodes are, the lower the detection distance is, which occurs

mainly when the electrodes spacing is < 2 mm.

AN4038 Datasheet(PDF) 19 Page - STMicroelectronics