A silicon carbide high gain differential amplifier for extreme temperature applications

In this paper, a high temperature, high gain differential amplifier based on a custom-built silicon carbide (SiC) N -channel junction field effect transistor (JFET) only, without using complementary P-channel devices is proposed. The operation principle of this active load differential amplifier is discussed, and the expression of the differential gain is derived. A prototype circuit is fabricated using thick film process on an alumina substrate and tested from room temperature up to 500 degrees C to demonstrate the high temperature capability of the proposed differential amplifier. The differential gain of 50.8 dB is achieved with 58.6 dB common-mode rejection ratio (CMRR) and 9.1 MHz gain bandwidth product (GBW) at 500 degrees C. Excellent linearity and low output impedance of the proposed differential amplifier are also demonstrated at various temperatures. The proposed SiC JFET high gain differ-ential amplifier can serve as a fundamental building block of the signal conditioning circuitry to be integrated with the sensing element for extreme environment applications.