A 40 Gb/s clock and data recovery (CDR) module for a fiber-optic receiver with improved phase-locked loop (PLL) circuits has been successfully implemented. The PLL of the CDR module employs an improved D-type flip-flop frequency acquisition circuit, which helps to stabilize the CDR performance, to obtain faster frequency acquisition, and to reduce the time of recovering the lock state in the event of losing the lock state. The measured RMS jitter of the clock signal recovered from 40 Gb/s pseudo-random binary sequence (2 31 -1) data by the improved PLL clock recovery module is 210 fs. The CDR module also integrates a 40 Gb/s D-FF decision circuit, demonstrating that it can produce clean retimed data using the recovered clock.
Significant performance improvements have been obtained with a 40 Gb/s phase-locked clock recovery (CR) module for fiber optic receivers by employing a new frequency acquisition circuit in the phase-locked loop (PLL) and a clock hold circuit. The new simple frequency acquisition circuit helps to extend the frequency lock-range, obtain faster frequency acquisition, and reduce the current consumption as compared with the conventional ones. In addition, a clock hold circuit helps to prevent the loss of the clock signal in the cases of temporary input signal loss. The measured RMS jitter of the improved PLL CR module at 40 Gb/s is about 250 fs, which is significantly better than the open-loop type CR module.
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