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Converters enable precise touch control

Posted: 14 Jun 2007 ?? ?Print Version ?Bookmark and Share

Keywords:capacitance-to-digital converter? touch controller? I2C?

AD7147 CapTouch controller from ADI

Cellphones, multimedia players, digital cameras and other rapidly shrinking mobile devices increasingly require new user interfaces to replace mechanical switches. Analog Devices Inc.'s new capacitance-to-digital converter (CDC) is a highly integrated touch controller that allows designers to quickly and easily add responsive user controls, such as scroll wheels and touch pads, to portable electronic devices.

As the newest addition to ADI's family of CapTouch controllers for consumer applications, the AD7147 provides highly accurate measurement and responsiveness and features the addition of an active shield feature for improved noise performance. Requiring only a single PCB for full implementation, the new CDC is ideal for ultra-thin mobile electronic devices.

The configurable AD7147 CDC features 13 capacitance inputs and femto farad resolution, allowing mobile electronics designers to implement a touch pad, scroll wheel, slider or up to 36 buttons per device. The addition of integrated active shield technology protects the AD7147 from capacitance-to-ground pickup and other noise sources in the system, allowing designers the freedom to place the sensor away from the main system IC.

The analog front-end of the AD7147 has been improved, yielding a threefold improvement in sensor response compared to previous AD714x products. The improved response allows end-users to experience more accurate finger navigation and improved device performance, while continuing to offer designers per-channel sensitivity adjustment for sensor-response fine-tuning. AD7147 includes on-chip sensitivity algorithms that compensate for changes in temperature and humidity, and ensure that users with different finger sizes receive the same responsive sensor performance.

AD7147 typically consumes 1mA in full power mode and just 50mA in low-power mode, a 20 percent reduction compared to competitive products on the market. The AD7147 also has the industry's lowest shutdown power consumption at only 2mA.

The AD7147 includes an SPI-compatible serial interface, while the AD7147-1 features an I?C-compatible serial interface. Both devices are sampling now and will be available in full production quantities in July. Priced at $1.30 each in 1,000-unit quantities, both products are housed in 24-pin 4-by-4mm LFCSPs.

- Henri Arnold
EE Times Europe

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