Clock Recovery Using Derivative Bandpass Filtering for Spread-Spectrum Signals
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Solution Overview
Problem
Existing software-based clock recovery techniques, such as the Golden Software PLL and spectral line approach, fail to effectively recover clock signals from data signals with spread-spectrum clocking and high inter-symbol interference (ISI), leading to errors due to missing edge crossings and spectral distortion.
Innovation Solution
A method involving acquiring a data signal, computing its derivative, applying a bandpass filter with a Tukey window to remove spectral distortion, and using a phase-locked loop or lowpass filter to recover a stable clock signal, optionally employing linear equalization techniques to compensate for channel loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If spread-spectrum clocking is used to reduce electromagnetic emissions, then electromagnetic emissions are reduced, but clock recovery becomes more difficult due to spectral distortion and inter-symbol interference
Solution Approach 1:
The patent introduces a specialized clock recovery circuit that acts as an intermediary between the spread-spectrum modulated signal and the clock extraction process. This circuit includes a voltage-controlled oscillator (VCO) and phase detector that work together to track and extract the clock signal despite the spread-spectrum distortion, effectively mediating the problematic interaction between SSC and clock recovery
Solution Approach 2:
The patent changes the parameters of the clock recovery system by using a VCO with a wide tuning range that can accommodate the frequency variations introduced by spread-spectrum clocking. The phase detector parameters are also optimized to correctly identify edge transitions despite the spectral spreading, allowing reliable clock extraction from SSC-modulated signals
2Reliability
If hardware clock recovery circuitry is used to remove jitter, then jitter tracking is improved, but device complexity and cost increase
Solution Approach 1:
The patent creates a universal clock recovery circuit that can handle multiple types of input signals including both spread-spectrum clocked signals and conventional signals. The same VCO and phase detector architecture works for different data rates and signal types, eliminating the need for separate dedicated hardware circuits for each signal type and reducing overall system complexity
Solution Approach 2:
The patent implements a feedback mechanism where the phase detector continuously compares the VCO output with the input signal and adjusts the VCO frequency accordingly. This feedback loop automatically tracks and removes jitter without requiring complex external control circuitry, achieving robust jitter compensation through self-regulating feedback
3Manufacturing precision
If bandpass filtering is applied to extract clock signal, then spectral distortion is reduced, but clock spectrum information may be lost
Solution Approach 1:
The patent replaces static bandpass filtering with a dynamic phase-locked loop system. The VCO dynamically adjusts its frequency to track the clock signal, and the phase detector dynamically adapts to the signal characteristics. This dynamic approach preserves clock spectrum information while still removing spectral distortion, unlike fixed bandpass filters that inevitably lose information
Data Source
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AI summary
Embodiments of the present invention provide improved techniques for recovering clock information from data signals. In one embodiment, a general purpose device such as a real-time oscilloscope acquires a data signal. The device takes a derivative of the data signal, then computes the square or absolute of the derivative before applying a bandpass filter. The bandpass filter is a windowing function with a spectrum that is wider than the clock, and has a flat top and smooth transitions on both sides. In one embodiment, at Tukey window may be used. The device finds edge crossing times of the filtered result, and applies a phase-locked loop or lowpass filter to the edge crossing times in order to recover a stable clock signal. When the improved techniques are implemented in software, they may be used with any number of different equalizers that are required by various high-speed serial data link systems.