Capacitance-to-digital converter utilizing digital feedback and auxiliary dac

Abstract

A capacitance-to-digital converter circuit s a capacitor bridge circuit to sense a difference in capacitance between sense capacitors and fixed capacitors in the bridge circuit. The sense capacitors vary according to a sensed parameter. Auxiliary capacitor digital to analog converters (DACs) are coupled to the capacitor bridge circuit to cancel the sensed difference. An analog to digital converter (ADC) receives a signal generated by the capacitor bridge circuit and the auxiliary capacitor DACs and converts the received signal to a digital signal. A digital accumulator accumulates the ADC output, whose output represents the difference in capacitance between the sense capacitors and the fixed capacitors. The accumulator output is used to control the auxiliary capacitor DACs to offset the difference in capacitance between the sense capacitors and the fixed capacitors. The accumulator output also provides the basis for the capacitance-to-digital circuit output.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)[0001]This application relates to the applications entitled “Circuit Including a Switched Capacitor Bridge and Method,” application Ser. No. 13 / 925,781, flied on Jun. 24, 2013, naming Louis Nervegna et. al., as inventors; and the application entitled “Capacitance to Digital Converter”, application Ser. No. 13 / 954,955, filed on Jul. 30, 2013, naming Louis Nervegna et. al., as inventors, which applications are incorporated herein by reference.BACKGROUND[0002]1. Field of the Invention[0003]This invention relates to capacitive-to-digital converters, and more particularly to capacitive-to-digital converters to sense a parameter using a bridge circuit.[0004]2. Description of the Related Art[0005]Capacitance-to-digital conversion plays an important role in many sensor applications such as measurement of pressure and humidity. In these sensing applications, key performance metrics include measurement range, resolution (i.e. rms noise of each measurem...

AI Technical Summary

Benefits of technology

The patent describes a circuit that uses a digital feedback network to reduce the impact of amplifier nonidealities on the performance of a capacitance-to-digital converter. A capacitor bridge circuit senses a difference in capacitance between sense capacitors and other capacitors in the circuit and uses auxiliary capacitor digital to analog converters (DACs) to reduce the sensed difference. An analog to digital converter (ADC) converts the signal generated by the bridge circuit to a digital signal, and a digital accumulator creates an accumulated digital signal based on the digital signal. The auxiliary capacitor DACs are controlled to offset the difference in capacitance between the sense capacitors and other capacitors in the bridge circuit based on the accumulated digital signal. The technical effect of this invention is to improve the performance of the capacitance-to-digital converter by reducing the impact of amplifier nonidealities.

Problems solved by technology

These amplifiers often pose performance limitations due to their finite DC gain, nonlinear gain characteristic, and limited output swing.

The finite DC gain and nonlinear gain characteristic of the amplifier can lead to nonlinearity in the capacitance-to-digital measurement characteristic, which degrades its accuracy performance.

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