Hiroki Matsumoto

A switched-capacitor charge-balancing analog-to-digital converter and its application to capacitance measurement

An analog-to-digital converter is developed based on the charge-balancing principle. It consists of a switched-capacitor integrator, comparator, and digital logic circuit. Driven by the two phase clock, the integrator accumulates consecutively the incremental signal charge while extracting the quantized reference charge from the accumulated signal charge each time its output becomes positive, to keep their charge balance. The ratio between the accumulated and extracted frequencies for a given period of time then provides the digital representation of an input analog signal. A conversion accuracy higher than 14 bits can be expected from its integrated realization because the offset voltage and the finite open-loop gain of an op-amp and the parasitic capacitance have no effect upon the conversion process. It also features a small device-count integrate onto a very small chip area. Some applications are also presented to demonstrate its validity.

A high-accuracy digital readout technique for humidity sensor

A high-accuracy digital readout technique of capacitance difference for a capacitive-type humidity sensor is presented. Based on the sigma-delta (EA) technique, the structure detects the relative humidity by providing a digital readout of capacitance change it causes. Analysis shows that the structure is insensitive to circuit imperfections, thus permitting the realization of digital readout with good accuracy. A resolution as high as 20 bits is achievable. Simulation results are given to confirm the effectiveness.

A digital hygrometer

A digital hygrometer using a polyimide capacitive humidity sensor is described. The capacitance change of the sensor due to absorption of water vapor in the atmosphere is detected by a digital switched-capacitor capacitance bridge controlled by a one-chip microcomputer and is displayed as relative humidity with 0.1% resolution. The accuracy of the hygrometer which is calibrated by the two-point method, is determined solely by the temperature dependence and the long-term drift of the dielectric sensitivity of the sensor and is estimated to be 2%. >

A switched-capacitor digital capacitance meter

A digital capacitance meter has been developed based on the switched-capacitor cyclic analog-to-digital (A/D) converter. It consists of the analog arithmetic and sample/hold (S/H) circuits. The arithmetic circuit first samples the capacitance to be measured in a form of its proportional voltage. This voltage is then converted into a binary number by the A/D converter. The whole operation is insensitive to parasitic capacitances, offset voltages of op amps, and the capacitance mismatch involved in the circuit. Therefore, the proposed meter permits an accurate capacitance measurement. Error analysis shows that 12-bit accuracy can be expected by realizing the meter in an IC form. A prototype meter built using discrete components and examples of measurement are also given.

Switched- capacitor frequency-to-voltage and voltage-to-frequency converters

Novel switched-capacitor circuits for the frequency-to-voltage (F/V) and voltage-to-frequency (V/F) conversion are presented. The circuit operation is insensitive to both the offset voltages of op-amps and parasitic capacitances. Therefore, the circuits allow the accurate conversion over the wide dynamic range. Experimental results are also given to confirm the principles of operation.