PSoC CY8CTMG20x and CY8CTST200 TRM, Document No. 001-53603 Rev. *C
87
TrueTouch Module
Figure 11-5. Relaxation Oscillator #2 Block Diagram
11.1.1.3
Successive Approximation
The successive approximation method provides a fast algo-
rithm for capacitance measurement for applications such as
detecting button presses. After a baseline is established, a
set of capacitive sensors are very quickly scanned. High
sensitivity can be achieved to enable scanning through a
large dielectric.
shows the hardware used in this
method. The successive approximation method is used for
proximity detection, fast button detection, and high resolu-
tion capacitance change measurement. The TrueTouch
Successive Approximation (CSA) User Module in
PSoC Designer™ uses this method.
In this method, an internal capacitor is connected to the ana-
log global bus. This bus contains ripple at the clock fre-
quency, which is filtered with a low pass filter leading into the
comparator. In addition, the IDAC current is set to the
desired value as explained later in this section.
Figure 11-6. Successive Approximation Block Diagram
The reference bus is connected to the analog global line to
initialize it to the Vr voltage (see
). After that, the
reference buffer is disconnected and not used. The sense
capacitance pin is now alternately grounded (see
) and connected to the analog global (see
). With the IDAC’s current driving onto this net,
the global net alternately charges and discharges a small
amount.
Figure 11-7. Initialization Phase for Successive
Approximation
An
alog G
lob
al B
us
Comparator
Mux
Mux
Refs
TrueTouch
Clock Select
RO Clock
IMO
CSCLK
Pin Enables
TrueTouch Logic
6-Bit Counter
16-Bit Counter
IDAC
CS1
CS2
CSN
IDAC
Anal
o
g G
lob
al
B
us
Vr
LP Filter
Closed
CSCLK
REF_EN
TrueTouch
Clock Select
IMO
CSCLK
Comparator
Mux
Mux
M8C Read
Reference
Buffer
Vr
CS1
CS2
CSN
C
INTERNAL
Vr
IDAC
Reference
Buffer
A
nal
og
Gl
ob
al
B
u
s
Vr
LP
Filter
Closed
Closed
Comparator
Mux
Mux
M8C Read
C
INTERNAL
CS1
CS2
CSN
Summary of Contents for PSoC CY8CTMG20 Series
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