A NOVEL FREQUENCY SYNTHESIZER CONCEPT FOR WIRELESS COMMUNICATIONS

The design of frequency synthesizers is especially challenging for wireless applications due to the requirements for high spectral purity, high frequency range, and fast tuning together with reasonable power consumption. In this paper, the idea of combining digital and analog techniques for achieving these goals is discussed. The proposed architecture uses I/Q modulation to translate a digitally synthesized tuneable low frequency tone to the final frequency range. In practice, mismatches between the I and Q branch amplitudes and phases as well as the local oscillator leakage can seriously degrade the spectral purity of the synthesized signal. A digital precompensation structure is presented to enhance the signal quality. The performance of the proposed synthesizer concept is illustrated using simulation results.