Two-Wire Analog Interfaces of Capacitance Sensors Based on GaAs Transistors

In this paper, the basic circuits of two-wire interfaces powered by a voltage source or a current source containing GaAs DpHEMT with an n-type channel and p-n-p HBT are investigated. Registration of signals of piezoelectric sensors with capacitance of about picofarad units requires reducing the influence of connecting cables on noise level and bandwidth. When operating the sensor at elevated temperatures, it is recommended to use an arsenide-gallium analog interface, where power supply and measured signals are transmitted via one cable. Based on the simulations, it is concluded that the best combination of parameters is possessed by the voltage-source powered interface containing cascode coupled DpHEMT and p-n-p HBT. The voltage-source and current-source powered interfaces are characterized by gain ratios of -4.827 and 0.823 and output resistances of 510 kOhm and 90 Ohms, and have less than 5% variation in gain over the input voltage range of -0.6 to 1 V and -0.3 to 1 V.