Jitter Minimization of Phase-locked Loops for OFDM-Based Millimeter-Wave Communication Systems with Beam Steering

Phased-lock loop rms phase jitter is modelled for millimeter-wave (mmWave) OFDM systems. Emphasis is placed on phased arrays for fast beam steering. A cascade of at least two phase-locked loops (PLL) is proposed, where a slow PLL with programmable output frequency in the lower GHz range drives one or more fast integer-N mmWave PLLs with separate digital phase control. The large loop bandwidth of the latter reduces its phase noise contribution from the voltage-controlled oscillator (VCO) and reduces the switching time of the PLL phase to below 100 ns. The crucial point in the optimization of the loop bandwidths is the anticipation of the phase noise reduction in the receiver, after the OFDM signal has been down-converted to the baseband. As a result, a low rms phase jitter can be combined with ultra-short phase switching times. The corresponding signal-to-noise ratio at the receiver output after common phase error correction is deduced from the PLL phase noise spectra, the number of PLLs in the phased array, and the sub carrier spacing.