CMOS for Extreme Radiation Environments

This paper presents the design of an experimen- tal first-order modulator with 4-bit internal quantization, fabricated in a 1.5- m space-qualified radiation-hard partially depleted silicon-on-sapphire (SOS) digital CMOS process. This converter architecture has been chosen partly to allow investiga- tion into the design of a range of common analog functions with two key issues in mind: one of technology and one environmental. First, both the architecture and the circuit design are optimized using a variety of unconventional techniques to account for the influence of extreme bias-dependent, radiation-induced threshold- voltage shifts of up to 1 V, as well as poor 1 device noise. Second, the circuitry is specially adapted to accommodate the floating-body behavior of this type of process, wherein drain conductance varies considerably with drain bias and frequency. The design techniques are directly applicable to very large- scale-integration silicon-on-insulator design, where similar device physics are encountered. Notwithstanding the severe constraints on the design, the fab- ricated circuit provides 9.7 bits of dynamic range in a 63-kHz signal bandwidth, only degrading to 9.1 bits after 23 Mrad(Si) of total dose radiation.