Silicon Carbide Differential Amplifiers for High-Temperature Sensing

This paper presents silicon carbide sensor interface circuits and techniques for MEMSbased sensors operating in harsh environments. More specifically, differential amplifiers were constructed using integrated, depletion-mode, n-channel, 6H-SiC JFETs and off-chip passive components. A three-stage voltage amplifier has a differential voltage gain of ~50 dB and a gainbandwidth of ~200 kHz at 450oC, as limited by test parasitics. Such an amplifier could be used to amplify the signals produced by a piezoresistive Wheatstone bridge sensor, for example. Design considerations for 6H-SiC JFET transimpedance amplifiers appropriate for capacitance sensing and for frequency readout from a micromechanical resonator are also presented.