Methods and apparatus for detecting a loss of lock condition in a clock and data recovery system

Methods and apparatus are provided for detecting a loss of lock condition in a clock and data recovery system. A loss of lock condition is detected in a clock and data recovery system that generates a recovered clock signal from a received signal by sampling the received signal for a plurality of different phases using one or more latches clocked by the recovered clock; evaluating the samples to monitor a data eye associated with the received signal; and detecting the loss of lock condition if the data eye does not satisfy one or more predefined conditions. Generally, the predefined conditions identify a loss of the data eye (e.g., when the data eye cannot be substantially detected), for example, based on a degree of opening of the data eye. The clock and data recovery system can optionally be restarted if the loss of lock condition is detected.