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 permanent 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.