© Quantum Research Group Ltd.
Short sample gate dwell times after the X
edges will limit the effect of moisture
spreading from key to key by taking
advantage of the RC filter-like nature of
continuous films; a short dwell time will limit
the time that the charge has to travel
through the impedance of the film (Section
3.13). This effect is independent of the
frequency of burst repetition, intra-burst
pulse spacing, or X drive pulse width.
Figure 1-5 QT60xx5B Basic Circuit Model
Sample
Sample
switch (1 of 8)
X drive
X drive
(1 of 8)
(1 of 8)
switch (1 of 8)
Y line
Y line
(1 of 8)
0
Cx
Cx
0
Cancellation
Cancellation
(1 of 8)
Xn
Xn
switches
switches
1
1
X
Y
Y
X
Reset switch
Reset switch
electrode
electrode
electrode
electrode
0
0
Cz1
Cz1
1
1
Burst mode operation permits reduced
power consumption and reduces RF
emissions, while permitting excellent
response time.
Cs
Cs
Cz2
Cz2
Ca
Ca
Cha rge
Cha rge
In te grator
In te grator
Xn
Xn
To 60xxx ADC
To 60xxx ADC
Amp
Am p
Reset
Reset
switch
switch
1.3 Matrix Configuration
S
S
a
a
m
m
p
p
lele
The matrix scanning configuration is shown
in Figure 1-5. The ‘X’ drives are sequentially
pulsed in groupings of bursts; an 8:1 analog
mux acts as the sample switch for all ‘Y’
lines. At the intersection of each ‘X’ and ‘Y’
line in the matrix itself, where a key is
s
s
w
w
it
i
c
tc
h
h
FFrroomm 6600xxxxxx
8-bit
8-bit
Offset DAC
Offset DAC
Offset Control
Offset Control
Amp
Amp
out
out
V
V
out
ou t
0
0
absolute signals yet still respond to very small signal
changes. Subranging is provided by two offset mechanisms
which can be thought of as 'coarse' and 'fine' offsets.
desired, should be an interdigitated electrode set similar to
those shown in Figure 1-2. The outermost electrode or the
key border should always be connected to an ‘X’ drive;
flooding the area around keys with X fill to a width of up to
10mm can help in suppressing moisture films further.
The 'coarse' method uses one or two switched Cz capacitors
to subtract charge from the charge integrator to create up to
two step offsets, to bring the analog signal back to a more
reasonable level. This action occurs during the course of the
burst.
Although it is referred to as a ‘matrix’, there is no restriction
on where individual keys can be located. The term ‘matrix’
refers to the electrical configuration of keys, not the physical
arrangement. Consult Quantum for application assistance on
key design.
The 'fine' method of offset uses an 8-bit R2R ladder DAC
driven by the X drive lines to create an offset in the amplifier
stage. The DAC is driven after the burst has ceased and the
charge accumulated, so there is no conflict in this dual-use of
the X lines.
1.4 Communications
The device uses two variants of SPI communications,
Slave-only and Master-Slave. Over this interface is a
command and data transfer structure
Figure 1-6 Circuit Block Diagram (8x8 Matrix Shown)
designed for high levels of flexibility using
minimal numbers of bytes. For more
information see Sections 4 and 5.
Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7
X0
X1
X2
X3
X4
X5
X6
X7
X0
X1
X2
X3
X4
X5
X6
X7
Device variations: Refer to Section 3.1 for
differences between the parts covered by
this datasheet.
SPI
to
Host
2 Signal Processing
✟
X{1..7}
X7
XS
The devices calibrate and process all
signals using a number of algorithms
specifically designed to provide for high
survivability in the face of adverse
environmental challenges. They provide a
large number of processing options which
can be user-selected to implement very
flexible, robust keypanel solutions.
Timing &
Charge
YC0 .
.
YC1
YC2 .
YC3
YC4 .
YC5
YC6 .
YC7
Neutralizing
Control
(PLD)
.
.
Transfer Strobe
Transfer Select
.
YS0..YS2
X0 .
.
X2 .
.
X4 .
.
X6 .
.
Transfer
M ux
X1
Signal Offset
Charge
R2R
DAC
X3
X5
XS
QT60xx5
AIN
Integrator
+
-
2.1 Negative Threshold
See also command ^A, page 24
Gain
✟
✟
“
Amp
The negative threshold value is established
relative to a key’s signal reference value.
The threshold is used to determine key
touch when crossed by a negative-going
signal swing after having been filtered by
Integrator Reset
CSR
Charge Cancellation 1
Charge Cancellation 2
CZ1
Cz1
Cz2
CZ2
lQ
5
www.qprox.com QT60xx5B / R1.06
QUANTUM [ QUANTUM RESEARCH GROUP ]
