High-performance All-digital Quadrature Frequency Synthesizer/mixer

In this paper, a high-performance all-digital quadrature frequency synthesizer/mixer applied to QAM modulation and demodulation is presented, which synthesizes 12-bit sine and cosine waveforms with a spectral purity of –83.0dB. The synthesizer covers a bandwidth from dc to 100 MHz in steps of 0.0466Hz with a corresponding switching speed of 5 ns at 200MHz clock frequency. Also, it is capable of frequency, phase and quadrature amplitude modulation. In this design, an efficient ROM look-up table method for calculating the sine and cosine function is employed, and a compression algorithm that only calculates one-eighth sine function is adopted to reduce the volume of ROM. By taking advantage of sine and cosine symmetries, the size of the ROM look-up table is only 1/51 of that of traditional one. The resulting chip fabricated in 0.35um five-level metal CMOS process has a complexity of about 20,000 gates with core area of 2.00 1.00 mm.