Capacitance-to-digital converter integrates DSP for on-chip data post-processing

November 08, 2017 // By Julien Happich
With a sampling rate up to 50kHz and resolving capacitance measurements down to 8aF, ams' PCap04 configurable capacitive sensing front end gives sensor manufacturers the ability to balance speed and resolution to match their design requirements.

When optimized for speed, the PCap04 can capture and digitize up to 50,000 sensor measurements per second. When sampling at a slower rate to optimize for precision, the PCap04 can achieve a measurement resolution of 8aF. 
The configurability of the device also enables sensor manufacturers to trade measurement speed off against power consumption. In low-power mode, the PCap04 draws a current as low as 4.0µA, making is suitable for battery-free operation on harvested energy. The PCap04 IC is intended for use with any sensing element that generates a change in capacitance. Featuring six capacitance measurement channels, it is well suited to use with sensing elements which measure parameters such as pressure, force, position, tilt, humidity, weight, level and many others.

The PCap04’s output may be supplied as a PWM or PDM representation of the raw measured capacitance value. The device also features a DSP to process the sensor measurements and convert them into digital values transmitted via an I 2C or SPI interface. It can handle input capacitance values over a broad range from as little as 1pF to as much as 100nF. The PCap04 provides various built-in configuration options, including support for grounded, floating, differential and differential grounded sensor connections. The DSP can run ams open-source code as well as user-generated code for functions such as measurement linearization and conversion. ams provides an evaluation kit and a user-friendly software development tool which make it easy for the design engineer to develop, test and debug code to run on the PCap04. The PCap04 is supplied as a bare die, or housed in a QFN-24 plastic package.

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