Feed-Forward Clock Recovery for Frequency-Shifted N-Ary Data
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Solution Overview
Problem
Current clock data recovery methods, particularly for high data rate serial transmission protocols, face challenges in handling n-ary signals and large frequency shifts, often resulting in latency issues and inefficiencies due to reliance on feedback structures like phase-locked loops.
Innovation Solution
A clock recovery module that accumulates edge timings, transforms them into a reference bit period, determines a time offset, and generates a reference clock signal, using a feed-forward structure to recover the clock signal, capable of handling n-ary signals and high data rates up to 10 Gbps with system clock rates of 250 MHz, while minimizing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase-locked loop based clock data recovery is used, then clock signal recovery is achieved, but latency increases due to feedback structure
Solution Approach 1:
The patent inverts the traditional feedback-based PLL approach by using a feed-forward structure. Instead of using feedback to correct phase errors, the system predicts and compensates for timing offsets in advance by accumulating edge timings and calculating expected edge positions, thereby eliminating the latency inherent in feedback loops while maintaining reliable clock recovery.
Solution Approach 2:
The system performs preliminary accumulation of edge timings and calculates expected edge positions before actual data reception. By pre-computing timing offsets and storing them in a lookup table, the system prepares compensation data in advance, avoiding real-time calculation delays and reducing overall latency in the clock recovery process.
2Loss of time
If blind oversampling is used, then latency is reduced, but frequency shifts due to spread-spectrum clocking modulation cannot be tracked
Solution Approach 1:
The patent incorporates feedback mechanisms in the form of accumulating actual edge timings and comparing them with expected edge positions. This feedback loop allows the system to track frequency shifts caused by spread-spectrum clocking modulation while maintaining low latency, as the feedback is used to update the lookup table rather than through a traditional PLL feedback path.
Solution Approach 2:
The system dynamically adjusts parameters by updating the lookup table with new timing offset values based on accumulated edge timings. This allows the system to adapt to frequency shifts and changing signal conditions while maintaining efficient operation, combining the speed of feed-forward processing with the adaptability of parameter updates.
3Adaptability or versatility
If phase interpolation techniques are used, then frequency shifts are tracked, but latency increases due to feedback control
Solution Approach 1:
The patent inverts the phase interpolation approach by using feed-forward timing offset compensation instead of feedback-based phase correction. The system accumulates edge timings and directly computes timing offsets to be applied in advance, eliminating the feedback control latency while maintaining the ability to track frequency shifts through continuous accumulation and lookup table updates.
4Area of stationary object
If digital solutions are used, then area is reduced, but performance degrades compared to analog solutions
Solution Approach 1:
The patent replaces analog mechanical components with digital processing elements. Instead of using analog phase detectors and voltage-controlled oscillators that occupy significant area, the system uses digital edge timing accumulation, lookup tables, and combinatorial logic to achieve clock recovery, significantly reducing device area while maintaining or improving performance through more precise digital timing control.
Data Source
AI summary
A method for recovering a clock signal from a data signal by using a clock recovery module is described. Edge timings of the data signal are accumulated. The edge timings accumulated are transformed into one reference bit period. A time offset for the reference bit period is determined. A reference clock signal is determined based on the time offset. The number of bits within a system clock of the clock recovery module is determined. The clock signal is recovered based on the reference clock signal and the number of bits. Further, a clock recovery module as well as a computer program are described.