Clock phase imbalance and phase noise in RF N-path filters

The quality of RF N-path filtering is limited by the performance of the involved multiphase clock. The paper presents analysis of critical clock imperfections. The phase imbalance that gives rise to an extra image band located at second harmonic frequency is analyzed by a linear periodically varying (LPV) model of a 4-path filter where the respective rejection ratio is estimated and verified by simulation. We also analyze the clock phase noise and devise that the reciprocal mixing is not diminished by the attained blocker rejection, however, in this case one can benefit from band limitation by the output capacitance of the driving transconductance amplifier (LNTA). The analysis is supported by simulation results.