Clock Recovery Circuit for Spread-Spectrum Frequency Tracking
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Solution Overview
Problem
Clock and data recovery circuits face increased processing load and reduced characteristics when both serial data and PLL clock signals are subjected to spread-spectrum frequency modulation, leading to doubled load and difficulty in tracking frequency deviations.
Innovation Solution
A clock recovery circuit is designed with a phase detector, frequency tracking loop, and phase interpolator that adjusts the clock signal phase based on frequency deviation detection, using spread-spectrum frequency modulation information to offset frequency modulation and reduce the frequency tracking load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If both serial data and PLL clock signals are subjected to spread-spectrum frequency modulation, then electromagnetic interference is reduced, but the processing load on the clock and data recovery circuit is doubled
Solution Approach 1:
The patent extracts and removes the spread-spectrum frequency modulation component from the frequency tracking loop. By separating the frequency modulation information and eliminating it through the frequency divider and phase detector, the circuit only needs to track the residual frequency deviation of the serial data, reducing the processing load by half while maintaining the electromagnetic interference reduction benefits of spread-spectrum modulation
Solution Approach 2:
The frequency tracking loop is segmented into distinct functional blocks: frequency divider, phase detector, and integrator. This segmentation allows the spread-spectrum frequency modulation information to be processed and removed in the frequency divider stage, enabling the rest of the circuit to focus only on tracking the essential frequency deviation without the burden of processing the full spread-spectrum signal
2Object-affected harmful factors
If both serial data and PLL clock signals are subjected to spread-spectrum frequency modulation, then electromagnetic interference is reduced, but frequency deviation tracking becomes difficult
Solution Approach 1:
The patent extracts the frequency modulation information from the PLL clock signal through the frequency divider, which divides the clock frequency by a variable factor corresponding to the spread-spectrum modulation. This extraction removes the frequency modulation component, leaving only the essential frequency deviation that needs to be tracked, thereby simplifying the detection and measurement process
Solution Approach 2:
The frequency divider acts as an intermediary between the spread-spectrum modulated clock signal and the phase detector. It mediates by converting the frequency-modulated clock signal into a form where the spread-spectrum component is eliminated, allowing the phase detector to cleanly compare phases without being confounded by the frequency modulation, thus facilitating accurate frequency deviation tracking
Data Source
AI summary
A frequency tracking loop receives a result from a phase detector that detects an advance and a retard of a phase between input data and an extracted clock signal, and conducts a control to reduce a frequency deviation between the input data and the extracted clock signal. A phase interpolator adjusts a phase of the clock signal subjected to spread-spectrum frequency modulation on the basis result of the frequency deviation in the frequency tracking loop, and outputs the extracted clock signal. In the frequency tracking loop, the frequency deviation between the data signal and the clock signal is corrected to offset a variation of the frequency of the clock signal, on the basis of the frequency modulation information related to the clock signal subjected to the spread-spectrum frequency modulation which is input to the phase interpolator. The frequency of the clock signal seemingly follows the frequency of the data signal.