QST608 ST Microelectronics, QST608 Datasheet - Page 7

• Manufacturer Part Number: QST608
• Description: Capacitive touch sensor device
• Manufacturer: ST Microelectronics

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QST608
3
3.1
3.2
QST touch sensing technology
Functional description
QST devices employ bursts of charge-transfer cycles to acquire signals. Burst mode permits
low power operation, dramatically reduces RF emissions, lowers susceptibility to RF fields,
and yet permits excellent speed. Signals are processed using algorithms pioneered by
Quantum which are specifically designed to provide reliable, trouble-free operation over the
life of the product.
The QST switches and charge measurement hardware functions are all internal to the
device. An external C
then measured. Larger values of C
rapidly, reducing available resolution. As a minimum resolution is required for proper
operation, this can result in dramatically reduced gain. Larger values of C
of differential voltage across it, increasing available resolution by permitting longer QST
bursts. The value of C
The device is responsive to both C
changes in sensor gain.
Figure 2.
Spread-spectrum operation
The bursts operate over a spread of frequencies, so that external fields will have minimal
effect on key operation and emissions are very weak. Spread-spectrum operation works
with the Detection Integrator mechanism (DI) to dramatically reduce the probability of false
detection due to noise.
SNSK_SCKn
SNS_SCKn
QTouch™ measuring circuitry
S
S
capacitor accumulates the charge from sense-plate C
can thus be increased to allow larger values of C
Sense capacitor
C
X
S
X
(a few nF)
and C
cause the charge transferred into C
S
, and changes in either can result in substantial
QST touch sensing technology
C
x
(~20 pF)
Earth
S
C
X
S
T
to rise more
to be tolerated.
(~5 pF)
reduce the rise
X
, which is
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