Reference-less Bang-bang CDR with Enhanced Frequency Acquisition Range Using Static and Modulated Integral Branch Offset Currents

This paper presents a technique to extend the frequency acquisition range for bang-bang phase-detector-based clock and data recovery (CDR) circuits without an additional frequency acquisition loop or lock detection circuit. The per-manent modulation of the offset current in the CDR's integral branch enhances the acquisition range by nearly 4 times, covering the entire tuning range of the voltage controlled oscillator. The increase in power dissipation and the chip area are negligible. This technique was implemented and measured in a 28 Gbps NRZ bang-bang CDR chip to confirm the working principle. In addition to the increased acquisition range, the CDR also surpasses jitter related specifications from the OIF CEI-28G-VSR standard.