Touch sensors need no MCU for control

Ultra-low-power touch-sensor chips are intended for portable applications such as mobile phones, PDAs, notebook PCs and media players.

STMicroelectronics has come up with a new family of ultra-low-power touch-sensor chips, following the signing of a technology-licensing agreement with the Korean company ATLab.

The sensors are intended for portable applications such as mobile phones, PDAs, notebook PCs and media players, as well as for the cost-sensitive white-goods market.

The new S-Touch family uses ATLab's capacitive touch-sensing technology, which is based on a fully digital architecture that needs no on-chip MCU, memory or firmware to implement control interfaces responsive to their users' touch.

The first products in the family are eight- and 12-channel devices.

This new hardwired touch-sensor family complements ST's recently announced MCU-based QST series, which enables intelligent touch-sensitive control interfaces for more complex applications and - at the other end of the scale - in simpler products where the sensor's MCU can also control multiple secondary functions.

The combined sensor portfolio positions ST as the only semiconductor supplier to provide a full range of touch-sensor solutions, meeting a wide spread of requirements and conditions across different industries.

ST has implemented the hardwired finite state machine, at the core of the S-Touch family, in optimised silicon, which requires very little power: consumption is around five to ten times lower than conventional touch-sensor solutions, with a sleep-mode consumption of just 1uA.

The sensor lines from the device to the application's touch pads do not need the external RC (resistor-capacitor) networks that are typically required in other solutions, and the sensors themselves are tiny - the 8-input device uses a 2.6 x 1.8mm QFN16 package - ensuring a very compact solution that is some 80% smaller than existing equivalent solutions, and highly cost-competitive.

The sampling time of the sensor, at 2ms, is also among the fastest in the industry Future products in this family will integrate proprietary technology from ST's new Xpander Logic family, which helps to overcome limitations in the number of I/O ports in MCU-based embedded systems by reassigning I/O-intensive tasks to an ultra-low-power Xpander Logic IC.

The technology allows an existing system processor to use a wide range of additional intelligent functions through a fast I2C interface, including a keypad controller capable of supporting up to 96 keys, with ghost key, multiple key and hotkey handling; and LED brightness control through a PWM controller.

By combining ST and ATLab IP in this way, S-Touch will be able to realise a true one-chip solution for a full user-interface controller, handling a full-size keypad with LED-backlighting control, and with capacitive touch-key and resistive touchscreen features.

ST also plans to explore the possibility of extending the collaboration with ATLab, especially in advanced digital IP design services in specific areas.

The technology provides an alternative to ST's MCU-based QST series, the two families ensuring the widest range of touch-sensing design options to meet styling, material and functional requirements.

Samples of the 12-channel STMPE1208 will be available within the first half of 2007, with volume production planned for September.

The 8-channel STMPE821 will be sampling in September 2007 and in volume production in January 2008.

The devices are priced at US $1.60 and $1.40, respectively, in quantities of 100,000 pieces.

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