| This thesis explores the use of commercially available SOI-CMOS technology for use in high-temperature sensor interface circuits for operation at temperatures up to 300°C. A fully depleted technology was chosen for its inherently low leakage current and critical sensor interface circuits were developed, specifically, a transimpedance amplifier and analog-to-digital converter. Since the ultimate goal is a high-temperature wireless microsensor, low power consumption and stable oscillator frequency were key issues in this work.; Oscillator topologies for MEMS resonators having very high series resistance were examined in regards power consumption and in-circuit quality factor. The transresistance topology was determined to be the best candidate for operation with MEMS resonators, but bandwidth and transimpedance gain must be very high to achieve a loop gain greater than one, as required for oscillation. An SOI transresistance was designed to meet the requirements of a particular SiC resonator. This IC was fabricated, packaged in a DIP, and tested. The amplifier, itself, oscillated due to parasitic coupling capacitance between input and output in the packaging, as proved by a variety of measurements and simulations. In future work, an unpackaged SOI-IC will be used to eliminate the parasitic coupling. Ideally, the MEMS resonator should be integrated with the IC.; To convert the analog signal to digital with 8-bit of accuracy reliably, a robust, 1st-order sigma-delta converter was designed. The sigma-delta converter is fully differential with discrete-time integrator and comparator, and also uses chopper stabilization, dynamic element matching and dithering to achieve high performance with relatively poor components. State-of-the-art performance has been achieved. With a power supply voltage of 3.3 V, SNR reached the theoretical maximum of 50 dB at room temperature, and was above 40 dB and 30 dB, respectively, up to 250°C and 275°C. Design weaknesses were identified in the course of testing, so it is believed that this performance can be improved. |
