Datasheet

CY8C21x34/B CapSense

Design Guide Document No. 001-66271 Rev. *B 25

Because it needs a lower switching frequency, you should use configuration when operating in an environment with

high C

, The relationship between C

and switching frequency is discussed in CapSense Performance Tuning with

User Modules.

3.8.3 CSDADC with PWM8 Clock Source

In this configuration, IMO is divided by an adjustable prescaler divider and used for the switched capacitor circuit on

the front end of the CSD. This configuration is more sensitive to noise at the frequency of operation and its

harmonics. This configuration requires two digital blocks.

This configuration is suitable for sensing through high-resistance materials (such as ITO) or when you want low

operation frequency because of emission problems.

3.8.4 CSDADC with VC2 Clock Source

In this configuration, the system clock is divided using an adjustable divider, VC2, and used for the switched-

capacitor circuit on the front end of the CSD. This configuration is more sensitive to noise signals at the frequency of

operation and its harmonics. This configuration requires one digital block.

This configuration is suitable for sensing through high-resistance materials (such as ITO) or when you want low

operation frequency because of emission problems.

3.9 CSDADC User Module Parameters

Figure 3-7. PSoC Designer - CSDADC Parameters Windows

3.10 Low-Level Parameters

3.10.1 Scanning Speed

This parameter sets sensor scanning speed. Although faster scanning speed provides good response time, slower

scanning speeds provide the following advantages:

 Improved SNR

 Better immunity to power supply and temperature changes

 Less demand for system interrupt latency; you can handle longer interrupts

See Table 3-1 and Table 3-2 for scanning speed and resolution performance. Possible values are Ultra Fast, Fast,

Normal, and Slow.

3.10.2 Resolution

This parameter determines the scanning resolution in bits. The maximum raw count for scanning resolution of N bits

is 2

N-1

. Increasing the resolution improves sensitivity and SNR, but reduces scan time. See Table 3-1 and Table 3-2

for scanning speed and resolution performance.

Possible values are 9 to 16 bits.