Optical Receiver Fractional Sampling Timing Recovery

The patent implements dynamic resampling and interpolation mechanisms that adapt the sampling rate to the actual symbol rate. The system uses a phase-locked loop (PLL) to dynamically adjust the sampling clock frequency, allowing the ADC to operate at lower rates when symbol rates are lower, while still supporting higher data rates when needed. This dynamic adaptation reduces the average complexity of the ADC system compared to fixed high-rate sampling.

The patent changes the sampling parameter from a fixed high rate to a variable rate that adapts to the symbol rate. By implementing fractional sampling where the sampling rate is a rational multiple of the symbol rate, and using digital resampling to convert to the desired output rate, the system achieves high data rate capability without requiring the ADC to always operate at the maximum possible sampling rate, thus reducing complexity.

The patent creates a universal sampling system that can handle multiple symbol rates through fractional sampling and digital resampling. The ADC is designed to sample at a fractional multiple of the symbol rate (e.g., 3/2, 5/4, 7/4 times the symbol rate), and a digital resampler converts these samples to the desired output rate. This multi-functional approach allows the same hardware to efficiently process different symbol rates without requiring rate-specific hardware configurations.

The patent introduces digital resampling as an intermediary process between the fractional-rate ADC output and the final symbol-rate data stream. The resampler acts as a mediator that converts samples taken at one rate to the desired output rate, enabling the system to maintain efficient fractional sampling while providing flexible output rates. This intermediary digital processing layer decouples the ADC sampling rate from the symbol rate, providing both efficiency and flexibility.

The patent implements feedback-based timing recovery mechanisms that use the fractional samples to detect and correct timing errors. The system employs a phase-locked loop (PLL) that continuously monitors the timing of received symbols and adjusts the sampling phase accordingly. The feedback loop compares expected symbol positions with actual sample positions and generates correction signals to maintain accurate timing synchronization, making timing recovery feasible even with fractional sampling rates.

The patent performs preliminary timing estimation and synchronization operations on the fractional samples before final data recovery. The system uses the fractional samples to pre-calculate timing offsets and phase corrections, which are then applied to align the sampling grid with the symbol boundaries. This preliminary timing adjustment simplifies the subsequent data detection process by ensuring that samples are taken at optimal points in the symbol waveform.