Touch sensor creates frugal keypad for handhelds

Quantum Research Group has developed a novel eight-key touch sensor IC that consumes just 40uA at 3V in low power mode.

Quantum Research Group, the charge-transfer (QT) capacitive touch company, has developed an eight-key touch sensor IC, the QT1080-ISG, that consumes just 40uA at 3V in low power mode.

Designed primarily for use in mobile phones, MP3 players, PC peripherals, remote controls and similar consumer devices, it enables eight touch keys through almost any panel material to facilitate a great variety of designs.

Other features include fully debounced results, lifetime automatic calibration, adjacent key suppression, low noise operation and a fast detection mode for use in applications where a simple touch slider is needed.

When used to implement individual touch keys, the sensitivity of each channel can be independently tuned simply by changing a capacitor.

Capacitive touch sensors have been notoriously prone to drift and unreliable operation.

The QT1080-ISG charge-transfer chip provides automatic drift compensation over-the life of the device to suppress false detections caused by changes in temperature, humidity or other environmental effects.

The device also self-calibrates on power-up and automatically recalibrates after long detections so that keys never "freeze" due to foreign objects in contact with the sensing surface or other unwanted influences.

Adjacent key suppression (AKS) is an included patent-pending feature that prevents multiple keys from responding to a single touch.

It works by comparing signal strengths within a group of keys and suppressing detections from those keys with signals which are weaker than the dominant, intended key.

AKS can operate across all eight keys or in two groups of four keys, or it can be disabled.

Spread spectrum, burst-mode operation ensures that external fields have minimal effect on key operation and heavily suppresses RF emissions A consensus filter that requires consecutive detections over a number of measurement cycles before a touch is confirmed, minimises the chances of false detection due to noise.

These features make EMC compliance tests simply a formality.

The device features a novel "wake from low power" mode that permits extremely low current consumption, typically 40uA, while retaining excellent normal response time once a key is touched.

This feature makes the QT1080 an excellent choice for portable applications such as MP3 players, mobile phones, and the like.

There are two output modes: one pin per key, and binary coded.

The QT1080-ISG operates from a single supply of between 2.8 and 5V DC and comes in a lead-free 1.1mm high QFN-32 package.

The QT1080 can be assessed using Quantum's E1080 evaluation board.

The E1080 provides a convenient reference design and allows the user to visualise discrete touch buttons and slider applications and also demonstrates back lighting.

The E1080 comes fully assembled and tested and ready to mount on the supplied plastic demo panel or to the inside of the user's end product.

It costs US $85 through distributors.

It is available now, priced at US $1 for high volume applications.

Only a handful of external passive components are required to produce an eight key control panel, leading to a very cost effective solution.

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