positive threshold level PTHR continuously for the PRD
period.
larger keys can be altered to compensate for this without
causing problems with key suppression.
After the PRD interval has expired and the auto- recalibration Adjacent key suppression works to augment the natural
has taken place, the affected key will once again function
normally. PRD is set on a per-key basis.
moisture suppression of narrow gated transfer switches
creating a more robust sensing method.
The functioning of the PRD setting is determined by an offset
to a lookup table, found on page 26. The values of time can
range from 0.1s to 25s. Setting the parameter to 0 will
disable the feature.
AKS Default value:
0 (Off)
5.9 Oscilloscope Sync - SSYNC
Pin 43 (S_Sync) can output a positive pulse oscilloscope
sync that brackets the burst of a selected key. More than one
burst can output a sync pulse as determined by the Setups
parameter SSYNC for each key.
PRD Typical values:
PRD Default value:
PRD Range:
5 to 8 (0.7s to 2.0s)
6 (1 second)
0..15 (∞, 0.1 .. 25s)
This feature is invaluable for diagnostics; without it,
observing signals clearly on an oscilloscope for a particular
burst is very difficult.
5.7 Burst Length - BL
The signal gain for each key is controlled by circuit
parameters as well as the burst length.
This function is supported in Quantum’s QmBtn PC software
via a checkbox.
The burst length is simply the number of times the
charge-transfer (‘QT’) process is performed on a given key.
Each QT process is simply the pulsing of an X line once, with
a corresponding Y line enabled to capture the resulting
charge passed through the key’s capacitance Cx.
SSYNC Default value:
0 (Off)
5.10 Negative Hysteresis - NHYST
The devices employ programmable hysteresis levels of
6.25%, 12.5%, 25%, or 50%. The hysteresis is a percentage
of the distance from the threshold level back towards the
reference, and defines the point at which a touch detection
will drop out. A 12.5% hysteresis point is closer to the
threshold level than to the signal reference level.
QT60xx6 devices use a fixed number of QT cycles which are
executed in burst mode. There can be up to 64 QT cycles in
a burst, in accordance with the list of permitted values shown
in Table 5.4.
Increasing burst length directly affects key sensitivity. This
occurs because the accumulation of charge in the charge
integrator is directly linked to the burst length. The burst
length of each key can be set individually, allowing for direct
digital control over the signal gains of each key individually.
Hysteresis prevents chatter and works to make key detection
more robust. Hysteresis is used only once the key has been
declared to be in detection, in order to determined when the
key should drop out.
Apparent touch sensitivity is also controlled by the Negative
Threshold level (NTHR). Burst length and NTHR interact;
normally burst lengths should be kept as short as possible to
limit RF emissions, but NTHR should be kept above 6 to
reduce false detections due to external noise. The detection
integrator mechanism also helps to prevent false detections.
Excessive amounts of hysteresis can result in ‘sticking keys’
that do not release. Conversely, low amounts of hysteresis
can cause key chatter due to noise or minor amounts of
finger motion.
The hysteresis levels are set for all keys only; it is not
possible to set the hysteresis differently from key to key.
BL Typical values:
BL Default value:
BL possible values:
2, 3 (48, 64 pulses / burst)
2 (48 pulses / burst)
16, 32, 48, 64
NHYST Typical values: 0, 1 (6.25%, 12.5%)
NHYST Default value:
1 (12.5%)
5.11 Dwell Time - DWELL
5.8 Adjacent Key Suppression - AKS
These devices incorporate adjacent key suppression (‘AKS’ -
patent pending) that can be selected on a per-key basis.
AKS permits the suppression of multiple key presses based
on relative signal strength. This feature assists in solving the
problem of surface moisture which can bridge a key touch to
an adjacent key, causing multiple key presses. This feature
is also useful for panels with tightly spaced keys, where a
fingertip might inadvertently activate an adjacent key.
The Dwell parameter in Setups causes the acquisition
pulses to have differing charge capture durations. Generally,
shorter durations provide for enhanced surface moisture
suppression, while longer durations are usually more
compatible with EMC requirements. Longer dwell times
permit the use of larger series resistors in the X and Y lines
to suppress RFI effects, without compromising key gain
(Section 2.8).
This setup lets the designer trade off one requirement for
with the other.
AKS works for keys that are AKS-enabled anywhere in the
matrix and is not restricted to physically adjacent keys; the
device has no knowledge of which keys are actually
physically adjacent. When enabled for a key, adjacent key
suppression causes detections on that key to be suppressed
if any other AKS-enabled key in the panel has a more
negative signal deviation from its reference.
DWELL typical value:
DWELL default value:
1 (187.5ns)
1 (187.5ns)
DWELL possible values: 0, 1, 2 (125, 187.5, 312.5ns
)
5.12 Mains Sync - MSYNC
This feature does not account for varying key gains (burst
length) but ignores the actual negative detection threshold
setting for the key. If AKS-enabled keys have different sizes,
it may be necessary to reduce the gains of larger keys to
equalize the effects of AKS. The signal threshold of the
The MSync feature uses the WS pin. The Sleep and Sync
features can be used simultaneously; the part can be put into
Sleep mode, but awakened by a mains sync signal at the
desired time.
lQ
22
QT60486-AS R8.01/0105
QUANTUM [ QUANTUM RESEARCH GROUP ]
