Effects of Subharmonics in LO Generation on RF Transceivers

Subharmonic residual in LO can degrade the performance of RF/mm-wave transceivers that employ frequency multipliers for LO generation. In this paper, we analyze the side effects that such subharmonics can cause. The effects are categorized to three parts: distortions in the up/down-converted signal, out-of-band emissions, and blocker tolerance in the receivers. A 60 GHz direct-conversion transceiver with a frequency tripler is taken for analysis. It is proved that there is no distortion or out-of-band emission issue with the presence of subharmonic in LO. For normal blocker tolerance requirements, the intrinsic subharmonic rejection capability in frequency multipliers is sufficient. In extreme cases, extra subharmonic filtering/rejection is needed.