A Reference-Less CDR Using SAR-Based Frequency-Acquisition Technique Achieving 55ns Constant Band-Searching Time and up to 63.64Gb/s/µs Acquisition Speed

Reference-less clock and data recovery (CDR) circuits are prevalently employed in applications that demand a continuous data rate due to their simplicity and cost-effectiveness, as they eliminate the need for an external reference [1]–[6]. The frequency acquisition (FA) speed of such CDRs is critical for link setup, particularly in systems with dynamic data traffic management that necessitate frequent transitions from sleep to wake up [7], [8]. According to [9], part of the links can be turned off without congesting the network, even in high-load scenarios like data centers. However, the interface wake-up delay has been identified as the most significant bottleneck in the overall network. To address this issue, this paper proposes a fast FA reference-less CDR using a successive approximation register (SAR)-based frequency band switching technique, achieving a constant band switching time of 55ns. With the help of the proposed charge pump (CP) with positive net current, the total FA time of less than 150ns is achieved, which is at least 4× shorter than comparable work.