CMOS/SOS Frequency Synthesizer LSI Circuit for Spread Spectrum Communications

Using a 3.5 $micro;m gate length complementary metal-oxidesemiconductor/silicon-on-sapphire (CMOS/80S) technology, a singlechip, radiation-hardened, direct digital frequency synthesizer has been developed. The circuit is a critical component of a fast-tuning wideband frequency synthesizer for spread spectrum satellite communications. Each clock period, the chip generates a new digitized sample of a sine wave, whose frequency is variable in 2 20 steps from dc to one-half the clock frequency. Operation at up to 7.5 MHz is possible in a worst case environment, including ionizing radiation levels up to 3 x 10 5 rads(Si). A computationally efficient algorithm was chosen, resulting in 12-bit output precision with only 1084 logic gates and 3840 bits of on-chip read-only memory (ROM). The accuracy of the algorithm is sufficient to maintain in-band spurious frequency components below ??-??65 dDc. At 300 mW, the chip replaces an MSI implementation which uses 25 integrated circuits and consumes 3.5 W.