Cypress CapSense CY8C20x36 Guía de usuario descargar pdf (Pagina 13)

Getting Started with CapSense

Document No. 001-64846 Rev. *I 13

Figure 2-5. Sensing Algorithm Output

2.3.3 CapSense with Sigma Delta Modulator (CSD)

Cypress‘s CSD method uses a switched capacitor circuit on the front end of the system to convert the sensor

capacitance to an equivalent resistor. A Sigma-Delta modulator converts the current measured through the equivalent

resistor into a digital count. When a finger is on the sensor, the capacitance increases and the equivalent resistance

+decreases. This causes an increase in current through the resistor, resulting in an increase in the digital count.

The CSD method requires a single dedicated pin and a single external component, C

MOD

, or two dedicated pins and

two external components, C

MOD

and R

, depending on what CapSense controller family is selected.

Figure 2-6 shows the CSD configuration for the CY8C21x34 CapSense controller family, and the family requires two

external components and two dedicated pins.

Figure 2-6. CY8C21x34/B CSD Block Diagram

Vdd

isensor

Sigma-Delta

Converter

Precharge

Clock

Cmod

High-Z

input

Sw1

Sw2

CY8C21x34/B

Gnd

ibleed

= External Connection

AMUX Bus

Vref

Rbus

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 ... 74 75

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Cypress CapSense CY8C20x36 Guía de usuario Pagina 13