CDR Frequency Acquisition Using Fixed Edge-Density Training Patterns
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Solution Overview
Problem
Synchronous Clock and Data Recovery (CDR) systems face challenges in frequency acquisition, particularly start-up complications, limited frequency capture range, and sensitivity to false-lock, requiring additional circuitry and accurate reference clocks, which can degrade performance and increase power consumption.
Innovation Solution
A method and system for frequency acquisition that uses edge counting in sets of samples to adjust the oscillator frequency, eliminating the need for an accurate reference clock and additional circuitry, by comparing the actual number of edges with an expected number in each sample set and adjusting the oscillator frequency accordingly, allowing for robust operation without parasitic loading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a clock-multiplier PLL loop is added next to the data-tracking loop for frequency acquisition, then the frequency capture range is improved and false-lock sensitivity is reduced, but the device complexity increases and power consumption increases due to requiring a rather accurate reference clock
Solution Approach 1:
The invention extracts the frequency acquisition function from the traditional separate clock-multiplier PLL loop and integrates it into the data-tracking loop itself. By using a programmable divider controlled by the data-tracking VCO output, the system performs frequency acquisition without requiring additional PLL circuitry or accurate reference clocks, thus reducing device complexity while maintaining frequency capture capabilities.
Solution Approach 2:
The invention merges the frequency acquisition function with the data-tracking loop by using the data-tracking VCO output to control a programmable divider. This combination allows the same circuitry to perform both frequency acquisition and data tracking, eliminating the need for separate clock-multiplier PLL loops and reducing overall system complexity.
2Reliability
If a toggling training pattern is applied to the input of the receiver for synchronization purposes with a PFD loop, then frequency acquisition capability is improved, but the device complexity increases and performance degrades due to additional parasitic loading on the input signal
Solution Approach 1:
The invention removes the need for external toggling training patterns and PFD loops by extracting the frequency acquisition capability from separate circuitry. Instead, it uses the existing data-tracking VCO output to control an internal programmable divider, eliminating the harmful parasitic loading caused by additional input circuitry while maintaining frequency acquisition capability.
Solution Approach 2:
The system performs frequency acquisition using its own internal resources - the data-tracking VCO output controls the programmable divider. This self-service approach eliminates the need for external training patterns and additional input circuitry, avoiding parasitic loading while maintaining autonomous frequency acquisition capability.
3Reliability
If additional amplifying buffer circuitry is added to drive the PFD with the low-swing differential input signal, then the frequency acquisition function is enabled, but the device complexity increases and bandwidth requirements increase
Solution Approach 1:
The invention extracts the frequency acquisition function from external buffer circuitry and PFD loops. By using the data-tracking VCO output to directly control an internal programmable divider, the system eliminates the need for additional amplifying buffer circuitry, reducing device complexity and bandwidth requirements while maintaining frequency acquisition functionality.
4Reliability
If the oscillator frequency is adjusted to bring the data rate within the CDR frequency capture range, then frequency capture reliability is improved, but the start-up time increases and frequency drift may still occur
Solution Approach 1:
The invention implements dynamic frequency adjustment by using the data-tracking VCO output to control a programmable divider. This dynamic approach allows the system to continuously adapt the division ratio based on the actual frequency conditions, enabling faster frequency capture and reducing start-up time compared to static pre-adjustment methods, while maintaining reliable frequency capture.
Data Source
AI summary
A method for frequency acquisition comprising steps of, acquiring samples of an input signal, each sample having edges, making sets with a fixed number of consecutively taken samples, numbering the edges in each set and determining a number of edges, comparing the number of edges in each set with an expected number of edges in the sets, increasing a frequency of a reference oscillator used in acquiring samples if the actual number of edges exceeds the expected number of edges, and decreasing the frequency of the reference oscillator used in acquiring samples if the expected number of edges exceeds the actual number of edges in a set.