Detection confirmation occurs by means of a ‘detect
integrator’ mechanism that requires multiple confirmations of
detection over a number of key bursts. The bursts operate at
alternating frequencies, so that external fields will have a
minimal effect on key operation. This spread-spectrum
mode of operation also reduces RF noise emissions.
1 Overview
The QT1100A is a 10 touch-key sensor IC based on
Quantum’s patented charge-transfer principles for robust
operation and ease of design. This device has many
advanced features which provide for reliable, trouble-free
operation over the life of the product. It can operate in either
a standalone mode or under host control via a serial
interface. Output options include UART and SPI serial types
and parallel scanport. In any interface mode, a low-cost
optional EEPROM can be used to determine the device
configuration using a stored Setup block.
The device also features the ability to acquire and lock onto
touch signals very rapidly, greatly improving response time
through the use of the ‘fast detect integration’ or ‘Fast-DI’
feature.
Sync Mode: The QT1100A features a Sync mode to allow
the device to slave to an external signal source, such as a
mains signal (50/60Hz), to limit interference effects. This is
performed using a special Sync pin.
FMEA self-testing: This part has been designed specifically
for demanding appliance applications requiring FMEA
certification. The part has many advanced features that
check for and report failures, to allow the designer to create
a safer product. It also features two robust serial interfaces
with sophisticated CRC error checking to permit validation of
commands and responses in real time.
Low Power Sleep Mode: The device features a low power
Sleep mode for microamp levels of current drain when not in
use. The part can be put into sleep for a certain percentage
of the time, so that it can still respond to touch but with lower
levels of current drain.
Burst mode: The device operates in ‘burst mode’. Each key
is acquired using a burst of charge-transfer sensing pulses
whose count can vary tremendously depending on the value
of the reference capacitor Cs and the load capacitance Cx.
The keys (also called ‘channels’) are acquired time
sequentially within fixed timeslots whose width can be
controlled by user-defined Setups.
AKS™ Adjacent Key Suppression works to prevent
multiple keys responding to a single touch, a common
complaint of capacitive touch panels. This system operates
by comparing signal strengths from keys within a defined
group to suppress touch detections from those with a weaker
signal change than the dominant key. The QT1100A allows
any AKS grouping of two or more keys, under user control.
Self-calibration: On power-up, all keys are self-calibrated
within a few hundred milliseconds to provide reliable
operation under almost any set of conditions.
Unique to this device is the ability for the designer to treat
each key as an individual sensor for configuration purposes.
Each key can be programmed separately for sensitivity, drift
compensation, recalibration timeouts, adjacent key
suppression, and the like.
The device is designed to support FMEA-qualified
applications using a variety of checks and redundancies.
Among other checks the component uses CRC codes in all
critical communication transfers, and can also output error
condition codes via redundant signaling paths.
Auto-recalibration: The device can time out and recalibrate
each key independently after a fixed interval of continuous
detection, so that the keys can never become ‘stuck on’ due
to foreign objects or sudden influences. After recalibration
the key will continue to function normally.
Drift compensation operates to correct the reference level
of each key slowly but automatically over time, to suppress
false detections caused by changes such as temperature,
humidity, dirt and other environmental effects.
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 ‘detect
integrator’ (DI) mechanism to dramatically reduce the
probability of false detection due to noise.
LQ
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Copyright © 2003-2005 QRG Ltd
QT1100A-ISG R3.02/1105
QUANTUM [ QUANTUM RESEARCH GROUP ]
