An 800 MHz quadrature digital synthesizer with ECL-compatible output drivers in 0.8 /spl mu/m CMOS

Direct digital frequency synthesizers (DDFS) play an important role in modern digital communications and instrumentation. They offer many advantages including fast continuous-phase switching response, fine frequency resolution, large bandwidth, good spectral purity, and low phase noise. The architecture in this design uses a phase accumulator to address a ROM look-up table that stores the sine samples. The input word (frequency-control word) to the phase accumulator controls the frequency of the generated sine waveform. This chip has modulation capabilities that include frequency modulation and phase modulation. Frequency modulation is performed by directly modulating the frequency control word and phase modulation is obtained by adding a phase offset to the phase accumulator output before addressing the ROM look-up table. The 7.2/spl times/7.9 mm/sup 2/ 94,000 transistor chip dissipates 3 W at 5 V and 800 MHz.