qt60325b-as Quantum Research Group, qt60325b-as Datasheet - Page 5

• Manufacturer Part Number: qt60325b-as
• Description: 32, 48, 64 Key Qmatrix? Keypanel Sensor Ics
• Manufacturer: Quantum Research Group

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.
lQ
(1 of 8)
Q T60xx 5
Q T60xx 5
X drive
(1 of 8)
X drive
SP I
SP I
to
to
Host
Host
electrode
To 60xxx AD C
electrod e
To 60 xxx AD C
From 60xxx
O ffset Control
From 60xxx
O ffset Control
Y S0. .Y S2
Y S0. .Y S2
Figure 1-6 Circuit Block Diagram (8x8 Matrix Shown)
Y C1
Y C1
Y C3
Y C3
Y C5
Y C5
Y C7
Y C7
Y C 0 .
Y C 0 .
Y C 2 .
Y C 2 .
Y C 4 .
Y C 4 .
Y C 6 .
Y C 6 .
C SR
C SR
C z1
C z1
C z2
C z2
AIN
AIN
X n
Xn
X 0
X 0
X 1
X 1
X 2
X 2
X 3
X 3
X 4
X 4
X 5
X 5
X 6
X 6
X 7
X 7
XS
XS
.
.
.
.
.
.
.
.
Figure 1-5 QT60xx5B Basic Circuit Model
X
X
✟
✟
Integrator R eset
Integrator R eset
C harge C ancellation 1
C harge C ancellation 1
C harge C ancellation 2
C harge C ancellation 2
X
X
{1. .7 }
{1. .7 }
XS
XS
X1
X1
X3
X3
X5
X5
Cx
Cx
X0 .
X0 .
X2 .
X2 .
X4 .
X4 .
X6 .
X6 .
Y
Y
electrode
e lectrod e
N eutralizin g
N eutralizin g
.
.
.
.
.
.
.
.
Timin g &
Timin g &
A m p
A m p
Ch arge
Ch arge
C ontrol
C ontrol
(PL D)
(PL D)
X 7
X 7
R 2R
R 2R
DA C
DA C
Offset DAC
O ffset DAC
(1 of 8)
(1 o f 8)
Y line
Y line
8-bit
8-bit
Signal Offset
Signal Offset
Reset sw itch
Res et sw itch
Transfer S trobe
Transfer S trobe
Transfer S elect
Transfer S elect
G ain
G ain
A mp
A mp
C s
C s
0
1
0
1
In te gr at or
In te gra tor
switch (1 o f 8)
switch (1 of 8)
C ha rg e
C ha rge
Sample
Sample
C
C
© Quantum Research Group Ltd.
✟
✟
Z1
Z1
0
1
C
C
0
1
Z2
Z2
C a
C a
C harge
C harge
Integrator
Integrator
switch
Sample
R eset
S ample
sw itch
R eset
sw itch
0
sw itch
X n
A mp
0
Cz1
Cz2
X n
A mp
out
Cz1
Cz2
X 0
X 0
X 1
X 1
X 2
X 2
X 3
X 3
X 4
X 4
X 5
X 5
X 6
X 6
X 7
X 7
out
“
“
Y0 Y1 Y2 Y 3 Y 4 Y 5 Y 6 Y 7
Y0 Y1 Y2 Y 3 Y 4 Y 5 Y 6 Y 7
Cancellatio n
switches
5
Cancellation
switches
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.
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
✟
✟
+
+
-
-
Transfer
Transfer
M ux
M ux
V
V
ou t
ou t
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.
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
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
command and data transfer structure
designed for high levels of flexibility using
minimal numbers of bytes. For more
information see Sections 4 and 5.
Device variations: Refer to Section 3.1 for
differences between the parts covered by
this datasheet.
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.
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
www.qprox.com
QT60xx5B / R1.06