A 14-to-32-Gb/s Deadzone-Free Referenceless CDR with Autocovariance-based Frequency Detector in 40-nm CMOS Technology

As data rate continues to rise in wireline communications, high-speed and low-cost clock and data recovery (CDR) has become a crucial part of receiver design [1]–[6]. The referenceless CDR has been explored to reduce hardware costs while maintaining wide-range operation because it does not require an external clock source. However, referenceless CDR should address several challenges. Since it does not receive synchronization information with the incoming data, the referenceless CDR should extract the corresponding frequency relying only on the data sequence. To achieve a wide and fast transient response, we adopt the stochasticbased FD (SFP) concept [1]. By collecting three consecutive data sequences and processing them correctly in Figs. 1(a), (b), and (c), the SFD shows remarkable locking behavior. However, in specific loop gain settings, they sometimes fall into the wrong frequencies and cannot escape that deadzone. Therefore, this manuscript thoroughly investigates when and why the deadzone occurs, and the new concept of autocovariance is introduced to prevent false locking.