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QT60161B Datasheet(PDF) 7 Page - Quantum Research Group |
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QT60161B Datasheet(HTML) 7 Page - Quantum Research Group |
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7 / 36 page  the suppression of multiple key presses based on relative signal strengths. AKS assists in solving the problem of surface water which can bridge a key touch to an adjacent key, causing multiple key presses, causing multiple key presses even though only one key was touched. This feature is also useful for panels with tightly spaced keys, where a fingertip can partially overlap an adjacent key. AKS works for keys that are AKS-enabled anywhere in the matrix and is not restricted to physically adjacent keys; the device has no knowledge of which keys are physically adjacent. When enabled for a key, adjacent key suppression causes detections on that key to be suppressed if any other AKS-enabled key in the panel has a more negative signal deviation from its reference. This feature does not account for varying key gains (burst length) but ignores the actual negative detection threshold setting for the key. If AKS-enabled keys in a panel have different sizes, it may be necessary to reduce the gains of larger keys relative to smaller ones to equalize the effects of AKS. The signal threshold of the larger keys can be altered to compensate for this without causing problems with key suppression. AKS works to augment the natural moisture suppression capabilities of the device (Section 3.10), creating a more robust touch panel. 2.10 Full Recalibration See also command ‘b’, page 24 The part fully recalibrates one or more keys after the ‘b’ command has been issued to it, depending on the current scope of the ‘b’ command. The device recalibrates all keys on powerup, after a hard reset via the RST pin or on power up, or via a reset using the ‘r’ command. Since the circuit tolerates a very wide dynamic signal range, it is capable of adapting to a wide mix of key sizes and shapes having widely varying Cx coupling capacitances. If a false calibration occurs due to a key touch or foreign object on the keys during powerup, the affected key will recalibrate again when the object is removed depending on the settings of Positive Threshold and Positive Recal Delay (Sections 2.2 and 2.7). Calibration requires 9 full burst cycles to complete, and so the time it takes is dependent on the burst spacing parameter (Section 3.8 also, ^G, page 22. 2.11 Device Status & Reporting See also commands ‘7’, page 19; ‘e’, page 19; ‘E’, page 20; ‘k’, page 20, ‘K’, page 20 The device can report on the general device status or specific key states including touches and error conditions, depending on the command used. Usually it is most efficient to periodically request the general device status using command ‘7’ first, as the response to this command is a single byte which reports back on behalf of all keys. ‘7’ indicates if there are any keys detecting, calibrating, or in error. If command ‘7’ reports a condition requiring further investigation, the host device can then use commands ‘e’, ‘E’, ‘k’ or ‘K’ to provide further details of the event(s) in progress. This hierarchical approach provides for a concise information flow using minimal data transfers and low host software overhead. 3 Circuit Operation A QT60161B reference circuit is shown in Figure 2-1. 3.1 Matrix Scan Sequence The circuit operates by scanning each key sequentially, key by key. Key scanning begins with location X=0 / Y=0. X axis keys are known as rows while Y axis keys are referred to as columns. Keys are scanned sequentially by row, for example the sequence Y0X0 Y0X1 Y0X2 Y0X3 Y1X0 etc. Each key is sampled from 1 to 64 times in a burst whose length is determined by Setup ^F. A burst is completed entirely before the next key is sampled; at the end of each burst the resulting analog signal is converted to digital using a single-slope conversion process. The length of the burst directly impacts on the gain of the key; each key can have a unique burst length in order to allow tailoring of key sensitivity on a key by key basis. 3.2 Signal Path Refer to Figures 1-5, 3-1, and 3-2. X-Drives. The X drives are push-pull CMOS lines which drive charge through the matrix keys on the positive and negative edges of X. Only the positive edge of X is used for signal purposes, however the negative edge must cause the charge across the keys to neutralize prior to the next positive edge, else the sampling mechanism will cease after one pulse. The part accomplishes this by holding all Y lines to ground during the falling edge of X. Charge gate. Only one X row is pulsed during a burst. Charge is coupled across a key's Cx capacitance from the X row to all Y columns. A particular key is chosen by gating the charge from a single Y column into a single one of four possible sampler capacitors. The other three X and three Y lines are clamped to ground during this process. Dwell time. The dwell time is determined internally and is the same as one oscillator period, i.e. 83.3ns with a 12MHz resonator. The dwell time is set via internal switching action ©Quantum Research Group Ltd. lQ 7 www.qprox.com QT60161B / R1.03 Figure 3-1 QT60161B Circuit Model X d rive (1 of 4) Y line (1 o f 4) X ele ctrode Y ele ctrode Cx C s (1 of 4) Do ne Start Result SM P CSB CSA R s (1 of 4) X |
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