Analysis of the Effect of Clock Skew Imperfection in ۴-phase High-QBand-pass Filters

In this paper the effect of clock skew on the behaviorof high-Q ۴-phase band-pass filters (BPFs) have beenthoroughly investigated. Exact mathematical derivations havebeen carried out to study the effects of such non-idealities asclock skew in the ۴-phase clock generator in a ۴-path filter.Using tedious mathematical analysis, it is proved that imagesignals from all frequencies fold back atop the desired RFvoltage, a phenomenon commonly ignored as previousderivations have been performed under the assumption ofperfect ۴-phase clock signals. In a real clock generator,however, this effect is present, degrading the performance andfiltering characteristics of the circuit. Simulation results provethat with only ۱o error in the phase of one LO signals, therejection of image signal which would otherwise be infinity isnow limited to about -۳۰dB.

Keywords:

High-Q Band-pass filters , N-path filters , Clock jitter , Clock skew , Harmonic fold-back (HFB).