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Low-power 14bit capacitive sensor rolls

Posted: 29 May 2009 ?? ?Print Version ?Bookmark and Share

Keywords:capacitive sensor? signal conditioning? DSP?

 ZMD31210 capacitive sensor

ZMD AG has expanded its family of capacitive sensor signal conditioning devices with the 14bit dynamic range ZMD31210 cLite IC.

The design offers 0.5 percent accuracy over a range of capacitance and temperature. Capacitive sensors offer several benefits, including very low power operation, and the ZMD31210 supports this with a 60?A current draw over a supply voltage range from 1.8V to 5.5V.

The ZMD31210 can be configured to interface with capacitive sensors from 2- to 260pF with sensitivity as low as 125aF per digital bit. The part accommodates both single and differential input sensor configurations.

The range of input capacitance, operating temperature and power supply voltage should make the chip suitable for industrial, consumer and medical applications, the company said.

"In close cooperation with key customers, we developed a digital technique to correct not only first-order, but also second-order nonlinearity errors difficult or impossible to correct with a pure analog signal path," said Thilo von Selchow, CEO at ZMD, in a statement. "Second-order correction is especially useful in humidity and pressure applications, but it can of course correct for sensor imperfections in almost any situation."

The ZMD31210 connects to microcontrollers but can also be utilized in stand-alone designs for transducer and switch applications. The mixed-signal design of cLite offers 14bit capacitive-to-digital conversion and full 14bit compensation of sensor offset, sensitivity and temperature via an internal DSP running a correction algorithm. Calibration coefficients are stored in an on-board non-volatile EEPROM. The system interface offers I?C, SPI, PDM or alarm outputs.

The standard supply voltage is 2.7V to 5.5V. At this voltage, accuracy is 0.25 percent over the -20C to +85C range, and 0.5 percent from -40C to +125C. The ZMD31210 offers a pin option for operation from 1.8V to 3.6V, with an accuracy of 1 percent from -20C to +85C.

The sleep mode feature reduces current draw to less than 1?A, making the device suitable for battery-based and other power-sensitive applications.

The ZMD31210 is targeted for volume production in Q4 09. Samples are available in TSSOP14 packages. Unit prices start at 2.09 euros or $2.93, in 1,000-unit volumes or more.

- Peter Clarke
EE Times Europe

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