Capacitance to Digital Converter using Dual Slope Technique

Now a days, mostly digital data processing is done because of high precision, power, bandwidth and area budget. When the sensors needs to be attached to a system with only digital inputs (microcontroller of low-cost) or when the sensor has to be located in a remote location, a digital output is preferred (e.g., in vehicle apparatuses). In most cases, obtaining a digital output requires first analog output generation and then digital conversion of it. Capacitance to Digital Converter (CDC) is a suggested interfacing circuit that transforms capacitance to a digital domain that may be easily handled. A CDC works on the similar principle as an analog to digital converter. Here, the CDC is implemented using dual slope technique but instead of using a single integrating capacitor, it uses a differential capacitive sensor element that varies by sensing a physical parameter, and the CDC generates a proportional digital output of the physical parameters sensed by the sensor. In this work, two different configurations of CDC that uses voltage source and current source are analysed in CADENCE software. The impact of non-idealities in the proposed technique on the converter’s performance is also explored. For the timing and control unit, a suitable counter was designed. Transmission gate based switch and the op-amp were designed using CADENCE software. The CDC is implemented using CMOS 180 nm technology for 8-bit with voltage source and current source and their accuracy is also analysed.