Multi-ring Cross-coupled VCO for Jitter Reduction
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Solution Overview
Problem
In high-speed chip-to-chip communication systems, existing Phase-Locked Loop (PLL) and Delay-Locked Loop (DLL) technologies face challenges in generating multiple phases of an oscillator signal to enable multi-phase processing, phase interpolation, and reducing clock jitter, which affects the reliability and efficiency of data detection.
Innovation Solution
The implementation of a two-ring voltage-controlled oscillator (VCO) system, where each ring generates a subset of phases of the oscillator signal, with inverse-phase locking and feed-forward signals, and a tail current is used to supply the rings, allowing for the generation of multiple phases and improved phase detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-ring VCO is used to generate oscillator phases, then the device complexity is low, but the ability to support multi-phase processing and reduce clock jitter is insufficient
Solution Approach 1:
The VCO is divided into two separate rings, each generating a subset of the required phases. Ring 1 generates phases φ0, φ1, φ2 while Ring 2 generates phases φ3, φ4, φ5. This segmentation allows each ring to be optimized independently and enables multi-phase processing capability without requiring a single complex ring structure.
2Adaptability or versatility
If multiple rings are used to generate multiple phases, then multi-phase processing capability is improved, but the device complexity increases
Solution Approach 1:
The two rings are cross-coupled and merged through shared tail current sources and phase comparison mechanisms. The rings work cooperatively to generate all six phases (φ0-φ5) with complementary relationships, achieving multi-phase processing capability while maintaining manageable complexity through systematic integration.
Solution Approach 2:
Each ring serves multiple functions: generating its subset of phases, providing feed-forward signals to the other ring, and participating in phase comparisons. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby managing complexity while enhancing versatility.
3Stability of the object's composition
If inverse-phase locking is implemented between rings, then clock jitter is reduced, but the control circuit complexity increases
Solution Approach 1:
Inverse-phase locking establishes a feedback mechanism where each ring's output phases are compared with the other ring's corresponding phases. The phase detectors generate error signals that feed back to the tail current sources, automatically adjusting the phases to maintain precise 180-degree relationships and reduce jitter.
4Speed
If feed-forward signals are added to accelerate phase transitions, then the switching speed is improved, but the circuit complexity increases
Solution Approach 1:
Feed-forward signals are generated in advance from each ring and applied to the other ring before the main phase transitions occur. This preliminary action pre-charges or pre-discharges the necessary nodes, accelerating the switching speed of phase transitions without requiring complex additional control logic.
Data Source
AI summary
Two rings of a voltage controlled oscillator (VCO) configured to generate a plurality of phases of an oscillator signal, each ring of the two rings comprising three stages of inverters configured to generate a subset of phases of the plurality of phases of the oscillator signal, cross coupled via each stage to a corresponding stage in an other ring of the two rings using inverters to inverse-phase lock the subsets of phases of the plurality of phases of the oscillator signal of the two rings, and configured to receive inputs at each stage from a previous stage in the ring and a feed-forward signal from a successive stage in the other ring of the two rings, and a tail current supply configured to supply the two rings of the VCO with a tail current, the tail current comprising a low-magnitude proportional component and a high-magnitude integral component.