Single Chip CDCs Link Capacitive Sensors

Emerging as the industry’s first single-chip, sigma-delta capacitance-to-digital converters (CDCs) for interfacing with capacitive sensors, the AD7745, AD7746, and AD7747 devices integrate all analog functions to reduce design effort and external components. Each device includes a 24-bit a/d converter, precision reference, clock, multiplexer, calibration registers, and a 2-wire serial interface. Other common specs include 2.7V to 5.25V operation, a noise figure of 10-18/vHz, power consumption of 1 mA maximum, and an operating temperature from -40°C to +125°C. The AD7745 is a single-channel device for use with floating sensors while the AD7746 is an otherwise-similar, two-channel version. The AD7747 is a single-channel device for use with grounded (one-electrode) sensors. Sampling now with production slated for April, prices range from $4.60 to $4.95 each/1,000. ANALOG DEVICES INC., Wilmington, MA. (800) 262-5643.