Analogue, Mixed Signal, LSI


Capacitance-to-digital converters

28 February 2022 Analogue, Mixed Signal, LSI

The AD7745 and AD7746 from Analog Devices are high-resolution Σ-Δ capacitance-to-digital converters. Their architecture features inherently high resolution (24-bit no missing codes, up to 21-bit effective resolution), high linearity (±0,01%) and high accuracy (±4 fF factory calibrated). The capacitance input range is ±4 pF (changing), while it can accept up to 17 pF common-mode capacitance (unchanging), which can be balanced by a programmable on-chip digital-to-capacitance converter.

The AD7745 has one capacitance input channel, while the AD7746 has two channels. Each channel can be configured as single-ended or differential. The AD7745/AD7746 are designed for floating capacitive sensors. For capacitive sensors with one plate connected to ground, the AD7747 is recommended.

The parts have an on-chip temperature sensor with a resolution of 0,1°C and accuracy of ±2°C. The on-chip voltage reference and the on-chip clock generator eliminate the need for any external components in capacitive sensor applications. The parts have a standard voltage input which, together with the differential reference input, allows easy interfacing to an external temperature sensor such as an RTD, thermistor or diode.


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