Cypress CapSense CY8C20x36 Guia do Utilizador descarregar pdf (Página 47)

Getting Started with CapSense

Document No. 001-64846 Rev. *I 47

Figure 3-22. Jitter Filter for Button Finger Touch

Unfiltered

Filtered

Unfiltered

Filtered

For more information about how to implement a jitter filter, see the code example CSA Software Filters with EzI2Cs

Slave on CY8C20xx6.

3.4.5 Event-Based Filters

Event-based filters involve a special filtering method where a pattern observed in the sensor data causes a

predefined response in the CapSense system. The pattern in the data is triggered by an event, such as a handheld

product being placed into a pocket, or V

dropping suddenly in a camera phone when the camera flash circuit is

being charged. One common response used with event-based filter is to block CapSense data transmission until the

pattern returns to normal. Another common response is to reset the level of the Baseline reference, defined in Signal-

to-Noise Ratio (SNR).

3.4.6 Rule-Based Filters

Rule-based filters are another special filtering method where a pattern observed in the sensor data causes a rule-

based response in the CapSense system. Unlike the event-based filter, the rule-based filter acts on patterns in the

sensor data that are encountered during normal operation of the touch surface. The rule-based filter takes into

account special scenarios on how sensors are used. For example, with a set of radio channel selection buttons, two

buttons can be pressed accidentally, but only one should be selected. The rule-based filter sorts out this kind of

situation in a predefined way.

3.5 Power Consumption

Minimizing power consumption is an important design goal. For many CapSense systems, extending battery life is

critical to the success of the product. In systems that do not use batteries, power consumption still plays a role in

optimizing power supply designs to reduce costs and PCB area.

3.5.1 Active and Sleep Current

Active current is the current consumed by the device when all selected analog and digital blocks are enabled and the

CPU is running. In typical applications, the CapSense controller does not need to be in the active state all the time.

The device can be put into the sleep state to stop the CPU and the major blocks of the device. Current consumed by

the device in sleep state is called sleep current. Sleep current is much lower than the active current.

3.5.2 Average Current

In typical applications, sleep state can be invoked periodically to reduce power consumption. This means that during

a preset time period, the CapSense controller wakes up from sleep state, performs all necessary operations in the

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