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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.  
o accomplish. Only a full recalibration via a reset or a  
2.8 Reference Guardbanding  
See also commands ^N, ^O, page 27; L, page 28  
recalibration command will perform a complete recalibration  
involving both the R2R Offset and Cz capacitors (Section  
2.10).  
QT60xx5 devices provide for a method of self-checking that  
allows the host device to ascertain whether one or more key  
reference levels are 'out of spec'. This feature can be used to  
determine if an X or Y line has broken, the matrix panel has  
delaminated from the control panel, or there is a circuit fault.  
After a fast recalibration has taken place, the affected key will  
once again function normally even if it is still being contacted  
by the foreign object. This feature is set on a per-key basis  
using setup ^L. It can be disabled if desired by setting this  
parameter to zero, so that it will not recalibrate automatically.  
Guardbanding alerts the host controller when the reference  
level of a key falls outside of acceptable absolute levels. The  
guardband is expressed in percent of absolute reference from  
the reference level of each individual key. The normal  
reference levels can be locked into internal eeprom via the  
Lock command 'L' during production; deviations in references  
that fall outside the guardbands centered on these reference  
levels are then reported as errors.  
2.6 Detect Integrator (DI)  
See also command ^J, page 26  
To suppress false detections caused by spurious events like  
electrical noise, the QT60xx5 incorporates a 'detection  
integrator' or DI counter that increments with each sample  
where the signal passes below the negative threshold, until a  
user-defined DI limit is reached, at which point the detection  
is confirmed and the corresponding detect bit is set.  
The calculations required for guardbanding are performed  
after the device has recalibrated or been reset after the L’  
command.  
If before the DI limit is reached, the signal rises to a point  
between the hysteresis and threshold levels, the DI counter is  
decremented with each such sample to a limit of zero.  
Positive excursion guarding is treated separately from  
negative excursion guarding. The possible negative settings  
are from 1% to 99% of absolute signal reference in steps of  
1% as set by command ^O. Positive excursions can run from  
10% to 1,000% in steps of 10% as set by command ^N. A  
setting of 0 disables the corresponding guardband direction.  
If before the DI limit is reached, the signal rises above the  
hysteresis level, the DI counter is immediately cleared.  
When an active key is released, the DI must count down to  
zero before the key state is cleared. Clearing a keys DI limit  
disables that key although the bursts for that key continue.  
Since the circuit uses a segmented ADC approach with a  
'coarse' (based on Cz states) and 'fine' (based on R2R ladder  
drive) offsets, the determination of percentage reference  
deviation from 'normal' presents a problem. The contributions  
of the Cz caps and the R2R ladder must be factored into the  
determination in order to make an accurate assessment of  
the error band. There are three commands which set  
coefficients used to convert the Cz and DAC offset values to  
'absolute signal' values, according to the following equation,  
for each key:  
The DI is extremely effective at reducing false detections at  
the expense of slower reaction times. In some applications a  
slow reaction time is desirable; the DI can be used to  
intentionally slow down touch response in order to require the  
user to touch longer to operate the key.  
There are 16 possible values for the DI limit.  
2.7 Positive Recalibration Delay  
See also command ^K, page 26  
TotalRef(k) = (C1 x nCz) + (C2 x Offset) + SigRef  
Where -  
TotalRef(k) is the equivalent absolute reference for key k;  
C1 is a global constant set by commands ^T and ^U;  
C2 is a global constant set by command ^V;  
nCz is the number of Cz caps switched in for key k;  
Offset is the noted value of the R2R DAC for key k;  
SigRef is the noted current 'window reference' for key k.  
A recalibration can occur automatically if the signal swings  
more positive than the positive threshold level. This condition  
can occur if there is positive drift but insufficient positive drift  
compensation, or if the reference moved negative due to a  
recalibration, and thereafter the signal returned to normal.  
As an example of the latter, if a foreign object or a finger  
contacts a key for period longer than the Negative Recal  
Delay, the key is by recalibrated to a new lower reference  
level. Then, when the condition causing the negative swing  
ceases to exist (e.g. the object is removed) the signal can  
suddenly swing back positive to near its normal reference.  
The percent deviations are computed in relation to  
TotalRef(k) on a per-key basis at the time the 'L' command is  
executed. Once the L command has recorded all values of  
relating to TotalRef into eeprom, the part will compare the  
actual running reference level of each key to its  
corresponding computed TotalRef value to see if it falls  
outside the guardbands specified by global parameters ^N  
and ^O.  
It is almost always desirable in these cases to cause the key  
to recalibrate to the new signal level so as to restore normal  
touch operation. The device accomplishes this by simply  
setting Reference = Signal.  
Values which correspond to the reference circuit of Figure 3-1  
are:  
The time required to detect this condition before recalibrating  
is governed by the Positive Recalibration Delay command. In  
order for this feature to operate, the signal must rise through  
the positive threshold level (Section 2.2) for the proscribed  
user-set interval determined by ^K.  
C1 = 1513; ^T value = 0x05, ^U value = 0xE9  
C2 = 8; ^V value = 0x08  
Guardbanding tests should not be confused with Reference  
Boundary errors (Section 2.11). Guardbanding can report  
errors that occur even if the signal is properly centered in the  
ADC window, while Reference Boundary error reporting  
cannot. Guardband tests do however require that the key  
After the Positive Recal Delay interval has expired and the  
fast-recalibration has taken place, the affected key will once  
again function normally. This interval can be set on a per-key  
basis; it can also be disabled by setting ^K to zero.  
lQ  
7
www.qprox.com QT60xx5 / R1.05