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This paper presents an 80-MHz 12-bit cryogenic low-power digital-to-analog converter (DAC) implemented in a 0.5-mum SiGe BiCMOS technology. The cryogenic DAC is capable of operating over an ultrawide temperature (UWT) ranging from -180degC to +120degC and under the high-energy particle radiation environment on the lunar surface. A bandgap voltage reference for the UWT applications is designed using SiGe heterojunction bipolar transistors, and the current-steering DAC is implemented using a segmented current source array. The design considerations for both extreme temperature and radiation environments are discussed. The cryogenic and radiation-tolerant DAC chip occupies a die area of 3.5 times 1.8 mm2 and consumes only 39.6 mW from a 3.3-V supply voltage. The maximum DAC sampling rate was measured at 80 MS/s at -180degC using a 40-pin dual in-line package.