A Cyclic RSD Analog-Digital-Converter for Application Specific High Temperature Integrated Circuits up to 250°C

Abstract

Silicon-on-Insulator (SOI) CMOS is the most commonly used technology for integrated circuits suitable for high temperatures and harsh environmental conditions. Data acquisition circuitry operating at these conditions has to consider the impact of wide temperature range operation. Therefore, the accurate operation of elementary building blocks is essential for proper system performance. To overcome the accuracy limitations set by channel leakage and performance degradation of NMOS and PMOS transistors, advanced circuit design methods are necessary. By introducing advanced leakage compensation, the overall performance of analog circuits at elevated temperatures is significantly improved. In this paper we present a cyclic analog-to-digital converter with a resolution of 12 bit, fabricated in a 1.0 μm SOI CMOS process. It utilizes the redundant signed digit (RSD) principle in a switched capacitor circuit and is thus insensitive to amplifier or comparator offset. In order to reduce the conversion error, leakage current compensated switches have been used. The ADC features two high gain operational amplifiers. Thereby a gain of more than 110 dB over the whole temperature range has been realized. The ADC's performance has been verified up to 250°C with an input voltage range from 0 V to 5 V. Preliminary results report an accuracy of more than 10 bits with a conversion rate of 1.25 kS/s. The supply voltage is 5 V with a maximum power consumption of 3.4 mW for the analog part of the circuit. The ADC is intended as an IP module to be used in customer specific mixed signal integrated circuits.