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1.7 Basic Power Modes

1.7.1 Overview

The device features a number of modes to set the currentdrain and speed of response.The available operating modes are:

2.4 AKS

TM

Adjacent Key Suppression

This patented feature works to prevent multiple keys fromresponding to a single touch. This can happen with closelyspaced keys, or a scroll wheel that has buttons very near it.AKS operates by comparing signal strengths from keys withina group of keys to suppress touch detections from those that have a weaker signal change than the dominant one.When enabled globally on the QT1106, AKS allows only oneindependent key, or the scroll section, to indicate a touch at a time. Additionally, the QT1106 has options for partial AKS; where some keys are included in the AKS operation andothers are not affected. In this case only one key in the AKSgroup can indicate a touch at any time; other keys can indicate touch in any combination. AKS can also be disabled. • Free Run - fastest detection response at all times • LP mode - low power, slower touch sensing response • Sleep - microamp-level current drain • Sync mode - for noise suppression of low frequencies

1.7.2 Free Run Mode

This mode uses a continuous stream of acquire bursts. FreeRun mode has, in consequence, the highest power drain of all the QT1106 operating modes but the fastest response time.

1.7.3 LP Mode

In LP (low power) mode, the QT1106 spends most of the time sleeping to conserve power; it wakes itself periodically toperform acquire bursts, then normally goes back to sleep again.The QT1106 provides a choice of intervals between acquirebursts to allow an appropriate speed/power trade-off to bemade for each product.

2.5 Autorecalibration (MOD)

The device can time out and recalibrate each keyindependently after a continuous touch detection that lasts forthe chosen ‘Maximum on-duration’ (MOD). This ensures that a key can never become ‘stuck on’ due to foreign objects orother external influences. After recalibration the key will continue to function normally.The nominal delay is selectable to be either 10s, 20s, 60s, or infinite (disabled), though the actual delay is different in someoperating modes (see Table 2.1). n/aSleep mode(vary with sync rate)10s, 20s, 60sSync mode(typ 55Hz sync)28s, 55s, 164sLP mode,760ms

1.7.4 Sleep Mode

In Sleep mode, the QT1106 shuts down to conserve power; it will remain in this mode forever or until the host wakes itusing the /SS pin.

Table 2.1 Maximum On-duration

Max on-durationsOperating Mode

1.7.5 Sync Mode

In this mode the device will synchronize to the host in a waythat allows for the suppression of heavy low frequency noise;for example, from mains frequencies and their harmonics.
1 response (120ms
2 )10s, 20s, 60sFree Run
1 response (200ms
2 )10s, 20s, 60sLP mode,200ms

QT1106 - 34853 2 Signal Processing

1 response (360ms
2 )10s, 20s, 60sLP mode,280ms

2.1 Power-up Self-calibration

1 response (680ms
2 )15s, 30s, 88sLP mode,440ms On power-up or after reset, all 10 channels are typicallycalibrated and operational within 650ms.

2.2 Drift Compensation

1 response times are estimated using a DI of six counts. This operates to correct the reference level of each key automatically over time; it suppresses false detectionscaused by changes in temperature, humidity, dirt and other environmental effects.
2 response times are estimated using a DI of two counts. Note: all response times are based on typical sensecapacitor values.The device also autorecalibrates all keys when one or morenormal keys’ signal reflect a sufficient decrease incapacitance from the reference level (signal error). If QMagicProximity modeis active, a signal error on the Proximity Key(Key 7) will only recalibrate itself. This is filtered in a mannersimilar to the DI filter; the decrease in capacitance must be seen for at least six successive cycles. Hence, in Free Runmode the device typically recalibrates within 400ms so as torecover normal operation quickly.

2.3 Detection Integrator Filter

Detect Integrator (DI) filter confirmation reduces the effects ofnoise on key states. The DI mechanism requires a specifiednumber of measurements that qualify as detections (and these must occur in a row) or the detection will not bereported.In a similar manner, the end of a touch (loss of signal) alsohas to be confirmed over several measurements. The QT1106 provides a choice of either two or six DImeasurements for confirming start of touch; end of touchalways uses two measurements. The DI mechanism works together with spread spectrumoperation to dramatically reduce the effects of noise.

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