Data Recovery Circuit Sampling Method Using Phase-Shifted Strobes
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Solution Overview
Problem
High-speed serial link systems face issues with asynchrony and skew due to mismatched semiconductor processes, wire-interconnect lengths, temperature variations, and material imperfections, leading to inaccurate data sampling, even with conventional over sampling techniques.
Innovation Solution
A sampling method using multiple strobes with the same frequency but different phase delays, where the positions of data transition points are determined using exclusive OR calculations to select the optimal strobe for sampling, ensuring accurate data sampling by adjusting the delay time to align bit middle points with sampling edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional over sampling technique is used, then sampling frequency is increased and accuracy is improved, but incorrect data sampling still occurs when skew is very large and sampling edges fall on data transition points
Solution Approach 1:
The patent divides the sampling process into multiple segments by using four different strobes (CLK0, CLK1, CLK2, CLK3) with different phase delays. Each strobe samples the digital signal at different time points, effectively segmenting the sampling process to cover various skew conditions. This segmentation allows the system to identify and select the most reliable sampling results among multiple attempts.
Solution Approach 2:
The patent changes the phase delay parameter of the strobes to resolve sampling errors. By adjusting the phase delays of CLK0, CLK1, CLK2, and CLK3 relative to each other, the system can adapt to different skew conditions and select the sampling results that are least affected by timing misalignment between data and clock signals.
2Measurement precision
If multiple strobes with different phase delays are used, then optimal sampling strobe can be selected to improve accuracy, but device complexity increases
Solution Approach 1:
The patent segments the sampling function across four different strobes, each handling a specific phase delay condition. This segmentation distributes the sampling task across multiple simple clock signals rather than requiring one complex adaptive clock, reducing overall system complexity while maintaining high sampling accuracy.
Solution Approach 2:
The patent uses four strobes (excessive action) to sample the same digital signal, which is more than the single strobe traditionally used. This excessive sampling approach ensures that at least one sampling instance will be correct even under varying skew conditions, and the selection logic chooses from these multiple samples to guarantee accuracy.
3Ease of operation
If sampling is performed at fixed edges of strobe, then sampling timing is simple to control, but sampling accuracy deteriorates when strobe and data are asynchronous due to process mismatch and temperature variations
Solution Approach 1:
The patent segments the clock signal into multiple strobes with different phase delays (CLK0, CLK1, CLK2, CLK3), each sampling at fixed edges but at different time points relative to the data signal. This segmentation allows the system to maintain simple fixed-edge sampling control while achieving high accuracy by selecting the best sampling result among multiple phase-offset attempts.
Solution Approach 2:
The patent performs preliminary sampling with multiple strobes having different phase delays before final data selection. This preliminary action with CLK0, CLK1, CLK2, and CLK3 allows the system to pre-identify the optimal sampling point under current skew conditions, ensuring accurate data capture without complex real-time adjustment during the actual sampling moment.
Data Source
AI summary
A sampling method and a data recovery circuit using the same are provided. The sampling method includes following steps. First, a first strobe, a second strobe, a third strobe, and a fourth strobe are provided, wherein the second strobe lags the first strobe a first predetermined phase, the third and the fourth strobe respectively lag the first and the second strobe a second predetermined phase, and the second predetermined phase is half of the first predetermined phase. Then, a digital signal is respectively sampled with the first and the second strobe. Thereafter, the positions of data transition points of the digital signal are determined according to the sampling results of the first and the second strobe. Next, the third or the fourth strobe is selected as a preferable sampling strobe according to the determination result. Finally, the digital signal is sampled with the preferable sampling strobe.