Takashi Takebayashi

A switched-capacitor interface for capacitive pressure sensors

A switched-capacitor interface of a capacitive pressure sensor is developed which provides linear digital outputs. It consists of a sample/hold circuit followed by a charge-balancing analog-to-digital converter. Two linearization methods based on the hyperbolic relation between the sensor capacitance and pressure are investigated in order to accommodate them to the basic interface configuration. In either method, linear digital outputs with an accuracy higher than 8-b are obtained. Because of its high accuracy and compatible fabrication process, the interface described is best suited for a smart silicon capacitive pressure sensor.<<ETX>>

A sensor signal processor

This paper describes a universal sensor interface named the sensor signal processor (SSP). The SSP consists of digital and analog blocks. The digital block generates a waveform which simulates the sensor characteristic in the time domain. An analog block processes a sensor output in the form consistent with the output of the digital block. Comparing both the outputs the SSP provides a linear digital equivalent of the measurand. For generating the waveform, the direct digital synthesis (DDS) and oversampling delta-sigma demodulation techniques are used. Eliminating precision devices, these techniques allow the high yield, monolithic implementation. The scale adjustment and cancellation of the offset and cross-sensitivity are also possible by adjusting the reference voltage involved in the DDS. Thus, the SSP satisfies almost all requirements for a universal interface. An application to a capacitive pressure sensor is also given to demonstrate its validity.<<ETX>>