Digital Clock Recovery for Jitter and Frequency Offset
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-speed optical communication systems face challenges in clock recovery due to timing jitter and frequency offset, particularly in coherent receivers, where traditional analogue implementations are inadequate and digital implementations are limited by processing speed and latency, leading to instability and reduced bandwidth.
Innovation Solution
A fully digital feed-forward clock recovery method is introduced, which determines the timing phase and frequency estimation over an observation interval, uses phase correction to adjust the interpolation phase, and employs a decimation mechanism to handle jitter and frequency offset, ensuring stability and high tolerance to timing jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a fully analogue clock recovery implementation is used, then bandwidth requirements of high-speed systems are fulfilled, but it is not feasible in a coherent receiver due to distortions (CD, PMD, nonlinear distortion, carrier frequency offset)
Solution Approach 1:
The patent replaces the analogue electronic system with a digital signal processing system. The digital implementation processes the received signal through ADC conversion and applies digital filtering, phase estimation, and frequency offset compensation algorithms to achieve clock recovery without requiring analogue components that cannot handle coherent receiver distortions.
2Reliability
If a digital clock recovery implementation is used, then impairments (at least CD) can be compensated, but processing speed of digital electronics in VLSI circuits is at least two orders of magnitude slower than high-speed optics
Solution Approach 1:
The patent performs preliminary processing of the received signal by accumulating samples over multiple symbol periods before making phase and frequency estimates. This preliminary accumulation allows the digital system to achieve sufficient processing speed by preparing data in advance, reducing the critical path delay and enabling real-time operation despite the inherent slowness of digital electronics.
3Reliability
If digital clock recovery is used, then impairment compensation is possible, but processing latency adversely affects bandwidth of clock recovery and limits ability to handle timing jitter
Solution Approach 1:
The patent implements a dynamic adaptation mechanism where the clock recovery parameters (phase and frequency estimates) are continuously updated based on incoming signal samples. The system adapts its estimation window and processing rate dynamically to balance latency and accuracy, allowing it to track timing jitter effectively while maintaining impairment compensation capabilities.
4Adaptability or versatility
If a hybrid analogue-digital clock recovery is used, then clock recovery can be implemented in CP-QPSK receiver, but a significant delay in the control loop is introduced by the compensator
Solution Approach 1:
The patent extracts and removes the delay-inducing compensator element from the control loop. By implementing a fully digital architecture that processes signals directly without requiring analogue compensator stages, the system eliminates the significant delay that would otherwise be introduced, while maintaining full compatibility with CP-QPSK receiver requirements.
Data Source
AI summary
A method and a device for processing a signal determine a timing phase over an observation interval of an input signal. A frequency estimation is determined based on the timing phase. A phase correction is determined for the observation interval based on the timing phase and the frequency offset. Then the phase correction is used to adjust the timing of the input signal. Also, a communication system with at least one such device is described.