Thursday, October 25, 2012

CY8C20224-12LKXI CapSense Analog System

CY8C20224-12LKXI CapSense Analog System
The analog system contains the capacitive sensing hardware.
Several hardware algorithms are supported. This hardware
performs capacitive sensing and scanning without requiring
external components. Capacitive sensing is configurable on
each GPIO pin. Scanning of  enabled CapSense pins are
completed quickly and easily across multiple ports.
Figure 1.  Analog System Block Diagram
Analog Multiplexer System
The analog mux bus connects to every GPIO pin. Pins are
connected to the bus individually or in any combination. The bus
also connects to the analog system for analysis with the
CapSense block comparator.
Switch control logic enables selected pins to precharge
continuously under hardware control. This enables capacitive
measurement for applications  such as touch sensing. The
analog multiplexer system in the CY8C20x24 device family is
optimized for basic CapSense functionality. It supports sensing
of CapSense buttons, proximity sensors, and a single slider.
Other multiplexer applications include:
■ Capacitive slider interface.
■ Chip-wide mux that enables analog input from any I/O pin.
■ Crosspoint connection between any I/O pin combinations.
When designing capacitive sensing applications, refer to the
latest signal to noise signal level requirements application notes,
which are found in > Design Resources
> Application Notes. In general, and unless otherwise noted in
the relevant application notes, the minimum signal-to-noise ratio
(SNR) requirement for CapSense applications is 5:1.

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