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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.  
3.5.2 NOISE  
C
OUPLING  
INTO Y LINES  
Figure 3-3 Relationship of X and Y signals  
External noise, sometimes caused by ground bounce due to  
injected line noise, can couple into the Y lines and cause  
signal interference in extreme cases. Such noise can be  
readily suppressed by adding a 100pF capacitor from each Y  
line to a ground plane near the QT60xx5.  
'n' pulses / burst  
R2R Value  
Xa  
Yb  
3.6 Burst Length & Sensitivity  
See also Command ^F, page 25  
Amp out  
The signal gain in volts / pF of Cx for each key is controlled  
by circuit parameters as well as the burst length.  
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 keys capacitance Cx.  
Xa  
Yb  
Yb'  
Yb  
QT60xx5 devices use a finite number of QT cycles which are  
executed in a short burst. There can be from 1 to 64 cycles in  
a burst, in accordance with the list of permitted values shown  
for command ^F, page 25. If burst length is set to zero, the  
burst is disabled but its time slot in the scanning sequence of  
all keys is preserved so as to maintain uniform timing.  
3.4.2 NOISE  
C
OUPLING  
I
NTO  
X
LINES  
External noise, sometimes caused by ground bounce due to  
injected line noise, can couple into the X lines and cause  
signal interference in extreme cases. Such noise can be  
readily suppressed by the use of series resistors as  
described above. Adding a small capacitor to the matrix line  
on the QT60xx5 side of the R, for example 100pF to ground  
near the QT60xx5, will greatly help to reduce such effects.  
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.  
Apparent touch sensitivity is also controlled by Negative  
Threshold (Section 2.1). Burst length and negative threshold  
interact; normally burst lengths should be kept as short as  
possible to limit RF emissions, but the threshold setting  
should be kept above a setting of 6 to limit false detections.  
The detection integrator can also prevent false detections at  
the expense of slower reaction time (Section 2.6).  
3.5 'Y' Gate Drives  
There are 8 'Y' gate drives (YC0..YC7) which are active-high;  
only one of these lines is used during a burst for a particular  
key. These lines are used to control the PLD to ground all  
unselected Ylines, making them low impedance. The  
selected Yline in the matrix remains unclamped by the PLD  
during the rising edge of the Xdrive line, during the time that  
the coupled charge from a single key is fed to the charge  
integrator via the 8:1 analog mux.  
3.7 Intra-Burst Spacing  
See also Command ^M, page 27  
The time between X drive pulses during a burst is the  
intra-burst pulse spacing. This timing has no noticeable effect  
on performance of the circuit, but can have an impact on the  
nature of RF spectral emissions from the matrix panel. The  
setting of this function can be from 2µs through 10µs, loosely  
corresponding to fundamental emission frequencies from  
500kHz and 100kHz respectively.  
There are also 3 Y-encoded lines YS0..YS2 which select the  
correct switch to actuate in the analog mux for the desired Y’  
line. Line YGfrom the controller acts to trigger the PLDs  
pulse generation circuit, whose pulse width following the rise  
of an Xline is dependent on an RC time constant. This  
pulse, YE, drives the enable pin of the QS3251 mux low  
(switch on) just before a positive-going Xdrive pulse, and  
high again (switch off) just after the Xdrive pulse. The time  
from the rising edge of an Xsignal to the rising edge of YE’  
is referred to as the dwell time, and this parameter has a  
direct effect on the ability of the circuit to suppress moisture  
films (see Sections 3.9 and 3.13).  
Longer spacings require more time to execute and can limit  
the operational settings of burst length and/or burst spacing  
(Section 5.7).  
The intra-burst QT spacing has no effect on sensitivity or  
water film suppression and is not particularly important to the  
sensing function other than described above.  
After the YEpulse has ceased, the controller and circuit act  
to ground all Ylines via the PLD just before the Xdrive  
signal goes low; this restores the charge across the matrix  
keys to a null state, making them ready for another sample.  
3.8 Burst Spacing  
See also Command ^G, page 25  
The interval of time from the start of one burst to the start of  
the next is known as the burst spacing. This is an alterable  
parameter which affects all keys.  
3.5.1 RFI FROM Y LINES  
Y lines are 'virtual grounds' and do not radiate a significant  
amount of RFI; in fact, they act as sinksfor RFI emitted by  
the X lines since they are virtual grounds. Series-R in the Y  
lines is not required for RFI suppression, and in fact series-R  
can introduce cross-talk among keys.  
Shorter spacings result in faster response time, but due to  
increasing timing restrictions at shorter spacings burst  
lengths are restricted, limiting the amount of gain that can be  
lQ  
12  
www.qprox.com QT60xx5 / R1.05