Device Variability Compensation in High Temperature Electronics for Hall Sensing Applications

We demonstrate high temperature electronics for next-generation aircraft, focusing on the realization of a monolithically integrated active Hall effect sensor in SiC. This circuit is required to operate at temperatures up to 450 °C. A novel approach to operational amplifier design is introduced, employing discrete 4H-SiC JFETs and investigates the resulting variability in circuit performance for JFET prameter mismatches, subsequently leveraging these insights to optimize performance at temperatures up to 200 °C. Traditionally, a pair of transistors with highly matched turn-on voltage, is required for the realisation of a differential pair, a fundamental building block in op-amp topologoes. A novel method to compensate for the mismatch in turn-on voltage has been developed in a differential pair, allowing for significant improvements in gain despite a 1.3 V difference in threshold voltage between input JFETs. The op-amp circuit utilizes careful resistor selection in the source follower stages to ensure DC offset symmetry and reduce the influence of variation in JFET conductivity in the subsequent amplifier stages. The op-amp experimentally demonstrates an open loop DC gain of 71.5 dB and is shown to be effective in feedback networks and circuits integrated with a SiC Hall bar. An op-amp differential amplifier with a 359 DC voltage gain and 84 Ω output impedance was developed, and this circuit design offers adjustable signal amplification and significantly improved performance characteristics compared to conventional amplifier topologies.