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QT100 Datasheet(PDF) 3 Page - Quantum Research Group |
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QT100 Datasheet(HTML) 3 Page - Quantum Research Group |
3 / 10 page Figure 2.4 SYNC Mode (Short Pulses) SNSK QT100 SYNC >10us >10us >10us 2.1.4 SYNC Mode It is possible to synchronize the device to an external clock source by placing an appropriate waveform on the SYNC pin. SYNC mode can synchronize multiple QT100 devices to each other to prevent cross-interference, or it can be used to enhance noise immunity from low frequency sources such as 50Hz or 60Hz mains signals. The SYNC pin is sampled at the end of each burst. If the device is in Fast mode and the SYNC pin is sampled high, then the device continues to operate in Fast mode (Figure 2.2). If SYNC is sampled low, then the device goes to sleep. From then on, it will operate in SYNC mode (Figure 2.1). Therefore, to guarantee entry into SYNC mode the low period of the SYNC signal should be longer than the b urst length (Figure 2.3). However, once SYNC mode has been entered, if the SYNC signal consists of a series of short pulses (>10µs) then a burst will only occur on the leading edge of each pulse (Figure 2.4) instead of on each change of SYNC signal, as normal (Figure 2.3). In SYNC mode, the device will sleep after each measurement burst (just as in LP mode) but will be awakened by a change in the SYNC signal in either direction, resulting in a new measurement burst. If SYNC remains unchanged for a period longer than the LP mode sleep period (about 70ms), the device will resume operation in either Fast or LP mode depending on the level of the SYNC pin (Figure 2.3). There is no DI in SYNC mode (each touch is a detection) but the Max On-duration will depend on the time between SYNC pulses; see Sections 2.3 and 2.4. Recalibration timeout is a fixed number of measurements so will vary with the SYNC period. 2.2 Threshold The internal signal threshold level is fixed at 10 counts of change with respect to the internal reference level, which in turn adjusts itself slowly in accordance with the drift compensation mechanism. The QT100 employs a hysteresis dropout of two counts of the delta between the reference and threshold levels. 2.3 Max On-duration If an object or material obstructs the sense pad the signal may rise enough to create a detection, preventing further operation. To prevent this, the sensor includes a timer which monitors detections. If a detection exceeds the timer setting the sensor perform s a full recalibration. This is known as the Max On-duration feature and is set to ~60s. This will vary slightly with Cs and if SYNC mode is used. As the internal timebase for Max On-duration is determined by the burst rate, the use of SYNC can cause dramatic changes in this parameter depending on the SYNC pulse spacing. 2.4 Detect Integrator It is desirable to suppress detections generated by electrical noise or from quick brushes with an object. To accomplish this, the QT100 incorporates a ‘detect integration’ (DI) counter that increments with each detection until a limit is reached, after which the output is activated. If no detection is sensed prior to the final count, the counter is reset immediately to zero. In the QT100, the required count is four. In LP mode the device will switch to Fast mode temporarily in order to resolve the detection more quickly; after a touch is either confirmed or denied the device will revert back to normal LP mode operation automatically. The DI can also be viewed as a 'consensus' filter, that requires four successive detections to create an output. lQ 3 QT100-ISG R3.06/0606 Figure 2.3 SYNC Mode (triggered by SYNC edges) SYNC SYNC SNSK QT100 SNSK QT100 slow mode sleep period sleep sleep sleep sleep sleep sleep Revert to Fast Mode Revert to Slow Mode slow mode sleep period Figure 2.2 Fast Mode Bursts (SYNC held high) SNSK QT100 SYNC ~1ms Figure 2.1 Low Power Mode (SYNC held low) SYNC SNSK QT100 sleep sleep sleep fast detect integrator OUT ~70ms |
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