Impact of loop delay on the performance of Gardner timing recovery

Feedback timing recovery schemes suffer from the delay in the feedback loop. Since this delay can be large in optical systems, especially when digital signal processing is implemented in FPGA, the performance of the phase-locked loop can be compromised when it has large loop bandwidth. In the letter, the performance of the digital feedback timing recovery scheme based on Gardner's detector is analyzed taking into account the delay in the loop and the phase noise that affects the local oscillators used for clocking data converters. Numerical results reported in the letter show that simulations closely fit the analysis.