CapSense Technology
CY8C20xx7/S CapSense
®
Design Guide
Doc. No. 001-78329 Rev. *E
15
raw counts to increase proportionally. By comparing the shift in steady state raw count level to a predetermined
threshold, the high-level algorithms can determine whether the sensor is in the ON (touch) or OFF (no touch) state.
Figure 2-7. CSD Raw Counts during a Finger Touch
The hardware parameters or the
CSD/CSDPLUS User Module Low-Level Parameters
DAC
and F
SW
, and the
firmware parameters or the
User Module High-Level Parameters
should be tuned to optimum values for reliable touch
detection. For a detailed discussion on tuning, see
CapSense Performance Tuning with User Modules.
2.2.2 CapSense Sigma Delta (CSD) PLUS
shows a block diagram of the CSDPLUS method for converting sensor capacitance (C
X
) into digital
counts. The main difference between CSDPLUS and CSD method is the number of I
DACs
used; CSDPLUS uses two
I
DACs
and the CSD uses a single I
DAC
.
The CSDPLUS method can be conceptually broken into two blocks
– switched-capacitor input, which converts
capacitance to current and sigma delta converter, which converts current to digital counts. Each block is explained in
the following sections.
