Synchronization-Phase Alignment of All-Digital Phase-Locked Loop Chips for a 60-GHz MIMO Transmitter and Evaluation of Phase Noise Effects

A phase-coherent technique for multiple all-digital phase-locked loops (ADPLLs) is presented and developed in this paper to target a 57-63-GHz multiple-input multiple-output (MIMO) transmitter (TX) with a digital beam-steering capability. The ADPLL TX chains are first fabricated in nanoscale CMOS and then time-synchronized and frequency- phase locked by a field-programmable gate array (FPGA) evaluation board. The calibration approach for phase alignment is carried out using a cancellation method to acquire the out-of-phase state within two ADPLLs. The accuracy of beam steering and phase alignment is investigated and analyzed based on a time-domain model for ADPLL to consider the impact of phase noise. The analysis results offer the required values of the ADPLL parameters to allow a millimeter-wave (mm-wave) MIMO TX with a highly accurate digital beam-steering capability.