Graduation date: 2006Circuits operating outside the earth’s atmosphere are more vulnerable to cosmic radiation and require special design consideration. The purpose of this work is to explore methods of mitigating the effect of radiation in phase locked loop (PLL) circuits. Several voltage controlled oscillators (VCOs) and two complete PLLs are designed and fabricated in a 0.35µm silicon on insulator (SOI) CMOS process. These circuits are characterized before and after exposure to total ionizing dose (TID) radiation to determine the effect of the radiation. This work shows that TID radiation has a relatively minor effect on PLL circuits in SOI process technology. All digital PLLs (ADPLLs) also provide increased resistance to radiation and thus are attractive for space applications. The design of a digitally controlled analog oscillator (DCAO), a key component of an ADPLL, is also presented.