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QT60325-AS 参数 Datasheet PDF下载

QT60325-AS图片预览
型号: QT60325-AS
PDF下载: 下载PDF文件 查看货源
内容描述: 32 , 48 , 64 KEY QMatrix KEYPANEL传感器IC [32, 48, 64 KEY QMatrix KEYPANEL SENSOR ICS]
分类和应用: 传感器
文件页数/大小: 42 页 / 810 K
品牌: QUANTUM [ QUANTUM RESEARCH GROUP ]
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© Quantum Research Group Ltd.  
Figure 1-2 Sample Electrode Geometries  
1 Overview  
QMatrix devices are digital burst mode charge-transfer (QT)  
sensors designed specifically for matrix geometry touch  
controls; they include all signal processing functions  
necessary to provide stable sensing under a wide variety of  
changing conditions. Only a few external parts are required  
for operation. The entire circuit can be built within 8 square  
centimeters of PCB area.  
PARALLEL LINES  
SERPENTINE  
SPIRAL  
Figure 1-1 Field flow between X and Y elements  
edge transitions of the X drive pulse. The charge emitted by  
the X electrode is partly received onto the corresponding Y  
electrode which is then processed. The parts use 8 'X'  
edge-driven rows and 8 'Y' sense columns to permit up to 64  
keys. Keys are typically formed from interleaved conductive  
traces on a substrate like a flex circuit or PCB (Figure 1-2).  
overlying panel  
X
Y
The charge flows are absorbed by the touch of a human  
finger (Figure 1-3) resulting in a decrease in coupling from X  
to Y. Thus, received signals decrease or go negative with  
respect to the reference level during a touch.  
element  
element  
Water films cause the coupled fields to increase slightly,  
making water films easy to distinguish from touch.  
QMatrix devices include charge cancellation methods which  
allow for a wide range of key sizes and shapes to be mixed  
together in a single touch panel. These features permit the  
construction of entirely new classes of keypads never before  
contemplated, such as touch-sliders, back-illuminated keys,  
and complex warped panel shapes, all at very low cost.  
1.2 Circuit Model  
An electrical circuit model is shown in Figure 1-5. The  
coupling capacitance between X and Y electrodes is  
represented by Cx. While the reset switch is open, a sample  
switch is gated so that it transfers charge flows only from the  
rising edge of X into a charge integrator. On the falling edge  
of X, the switch connects the Y line to ground to allow the  
charge across Cx to neutralize to zero. The voltage change  
on the output of the charge integrator after each X edge is  
quite small, on the order of a few tens of millivolts. Changes  
due to touch are typically under 0.1% of total integrator  
voltage. The X pulse can be  
The devices use an SPI interface running at up to 1.5MHz to  
allow key data to be extracted and to permit individual key  
parameter setup. The interface protocol uses simple single  
byte commands and responds with single byte responses in  
most cases. The command structure is designed to minimize  
the amount of data traffic while maximizing the amount of  
information conveyed.  
repeated in a burst of up to 64  
pulses to increase the change in  
integrator output voltage due to  
touch during an acquire (Section  
3.6) to increase gain.  
Figure 1-3 Field Flows When Touched  
In addition to normal operating  
and setup functions the device  
can also report back actual  
signal strengths and error codes.  
QmBtn software for the PC can  
be used to program the IC as  
well as read back key status and  
signal levels in real time.  
The charge detector is an opamp  
configured as an integrator with a  
reset switch; this creates a virtual  
ground input, making the Y lines  
appear low impedance when the  
sample switch is closed. This  
configuration effectively  
eliminates cross-coupling among  
Y lines while greatly lowering  
QMatrix parts employ transverse  
charge-transfer ('QT') sensing, a  
new technology that senses  
changes in the charge forced  
across an electrode by a digital  
edge.  
overlying panel  
X
Y
element  
element  
susceptibility to EMI. The circuit  
is also highly immune to  
The parts are electrically  
identical with the exception of the  
number of keys which may be  
sensed.  
capacitive loading on the Y lines,  
since stray C from Y to ground  
appears merely as a small  
parallel capacitance across a  
Figure 1-4 Fields With a Conductive Film  
virtual ground.  
1.1 Field Flows  
The circuit uses an 8-bit ADC,  
with a subranging structure to  
effectively deliver a 14-bit total  
conversion 'space' (see Figure  
1-6 and Section 3.3). In this way  
the circuit can tolerate very large  
Figure 1-1 shows how charge is  
transferred across an electrode  
set to permeate the overlying  
panel material; this charge flow  
exhibits a high dQ/dt during the  
lQ  
4
www.qprox.com QT60xx5 / R1.05