© Quantum Research Group Ltd.
Figure 1-5 QT60xx5B Basic Circuit Model
X drive
X drive
(1 of 8)
(1 of 8)
Xn
Xn
X
electrode
electrod e
Y line
Y line
(1
of
f
8)
(1
o 8)
Sample
Sample
switch (1 of 8)
switch (1 o f 8)
0
0
1
1
Cx
Cx
Y
electrode
e lectrod e
Cancellation
Cancellatio n
switches
switches
Res et sw itch
Reset sw itch
0
0
1
1
Cz1
Cz1
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.
Burst mode operation permits reduced
power consumption and reduces RF
emissions, while permitting excellent
response time.
+
+
+
+
Cs
Cs
To 60xxx AD C
60 xxx
mp
Am p
C ha rge
C ha rg e
In te gra
or
In te gr at
tor
Ca
Ca
Cz2
Cz2
X
X n
n
R eset
R eset
sw itch
switch
Sample
S ample
sw itch
sw itch
1.3 Matrix Configuration
The matrix scanning configuration is shown
in Figure 1-5. The ‘X’ drives are sequentially
pulsed in groupings of bursts; an 8:1 analog
V
V
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
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.
ou
ou t
t
From 60xxx
O ffset Control
8-bit
8-bit
Offset DAC
O ffset DAC
A mp
A mp
out
out
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.
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.
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.
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.
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
designed for high levels of flexibility using
Figure 1-6 Circuit Block Diagram (8x8 Matrix Shown)
minimal numbers of bytes. For more
Y0 Y1 Y2 Y 3 Y 4 Y 5 Y 6 Y 7
X0
information see Sections 4 and 5.
X0
X2
X2
X3
X4
X5
X6
X7
X3
X4
X5
X6
X7
XS
YC0
Y C1
YC2
Y C3
YC4
Y C5
YC6
Y C7
.
.
.
.
.
.
.
.
SP I
to
Host
K EYMATRIX
Transfer
M ux
+
X1
X1
Device variations:
Refer to Section 3.1 for
differences between the parts covered by
this datasheet.
✟
X
{1. .7 }
X7
2 Signal Processing
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.
Timin g &
Ch arge
N eutralizin g
C ontrol
(PL D)
Transfer S trobe
Transfer S elect
Y S0. .Y S2
X0 .
.
X2 .
X3
.
X4 .
X5
.
X6 .
XS
.
X1
Q T60xx 5
AIN
R 2R
DA C
Signal Offset
C harge
Integrator
G ain
A mp
✟
“
C
Z2
2.1 Negative Threshold
See also command ^A, page 24
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
✟
-
C SR
C z1
C z2
Integrator R eset
C harge C ancellation 1
C harge C ancellation 2
C
Z1
lQ
5
www.qprox.com
QT60xx5B / R1.06
QUANTUM [ QUANTUM RESEARCH GROUP ]
