Triple-Path CDR Circuit for Jitter Control and Loop Stability
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Solution Overview
Problem
CDR circuits face challenges with large jitter due to process variations, temperature variations, and timing uncertainties in high-speed data transmission, affecting oscillator performance and loop stability.
Innovation Solution
A clock and data recovery circuit with a triple-path structure that includes a sampling circuit, phase detector, processing circuits, and an oscillator circuit, utilizing a triple-path structure for bandwidth tracking and frequency adjustment, allowing for wide tuning range and high resolution despite temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional oscillator circuit is used in CDR, then the circuit structure is simple, but large jitter occurs due to process variations, temperature variations, and timing uncertainties
Solution Approach 1:
The oscillator control is segmented into three independent paths: a proportional path for phase adjustment, an integral path for frequency adjustment, and a feedforward path for bandwidth tracking. Each path processes control signals independently and combines them at the oscillator input, allowing separate optimization of jitter performance without requiring complete circuit redesign
Solution Approach 2:
The system dynamically changes oscillator parameters (phase and frequency) based on three different control signals that respond differently to input conditions. The proportional path provides immediate phase correction, the integral path eliminates steady-state frequency errors, and the feedforward path anticipates frequency changes, collectively reducing jitter across varying process and temperature conditions
2Adaptability or versatility
If the oscillator tuning range is increased to handle frequency variations, then adaptability improves, but loop stability deteriorates
Solution Approach 1:
Different portions of the tuning range are handled by different control paths with optimized characteristics. The proportional path handles small deviations near lock point with high stability, the integral path handles medium-range frequency corrections, and the feedforward path handles large frequency shifts. Each path is locally optimized for its specific operating region, maintaining overall loop stability across the full tuning range
Solution Approach 2:
The control system dynamically switches between different control mechanisms based on the magnitude of frequency deviation. When frequency errors are small, the proportional and integral paths provide stable closed-loop control. When large frequency shifts occur, the feedforward path becomes dominant, allowing rapid retuning without compromising loop stability during the transition
3Speed
If high-speed data transmission is implemented, then data rate increases, but timing uncertainties and jitter increase
Solution Approach 1:
The feedforward path performs preliminary frequency adjustment based on detected frequency errors before the main feedback loop completes its correction cycle. By anticipating required frequency changes and applying them in advance, the system reduces timing uncertainties that would otherwise accumulate during the feedback delay period, maintaining timing precision at high data rates
Data Source
AI summary
A clock and data recovery circuit includes a sampling circuit, a phase detector, a first processing circuit, a second processing circuit and an oscillator circuit. The sampling circuit is configured to sample input data according to an output clock, and generate a sampling result. The phase detector is configured to generate a detection result according to the sampling result. The first processing circuit is configured to process the sampling result to generate a first digital code. The second processing circuit is configured to accumulate a portion of the first digital code to generate a second digital code. A rate of change of a code value of the second digital code is slower than a rate of change of a code value of the first digital code. The oscillator circuit is configured to generate the output clock according to the detection result, the first digital code and the second digital code.