Multilevel Half-Rate Phase Detector for Clock and Data Recovery Circuits

In this brief, a half-rate (HR) bang-bang (BB) phase detector (PD) with multiple decision levels is proposed for clock and data recover (CDR) circuits. The combination allows the oscillator to run at half the input data rate while providing information about the sign and magnitude of the phase shift between the PD inputs. This allows a finer control of the frequency of the oscillator in the phase-locked loop (PLL) of the CDR circuit, which results in up to 30% less output clock jitter than with a conventional two-levels HR BB PD. Thanks to this, the bit error rate can be decreased by up to 5x in a 5-Gb/s CDR circuit. The proposed topology was implemented in a 28-nm FDSOI CMOS technology providing average power consumption below 76 mu W with a supply voltage of 1 V. Although multilevel (ML) BB PDs have already been proposed in some PLL-based CDR with very interesting results. a specific design of the PD has to be implemented for an HR system. This brief provides the first ML-HR-BBPD.