DCO Overlap Bypass Control for Limit Cycle Reduction in PLLs

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Solution Overview

Problem

Hybrid and digital phase locked loops (PLLs) experience limit cycles due to frequency redundancy in digitally controlled oscillators (DCOs) caused by DCO frequency overlap regions, leading to degraded jitter performance.

Innovation Solution

A method to detect the boundary of DCO frequency overlap regions and adjust the integral control signal to bypass these regions, reducing the amount of overlap by adjusting the control code, thereby minimizing limit cycles and jitter.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If DCO frequency overlap regions are used to ensure continuous frequency coverage, then frequency coverage continuity is improved, but limit cycles are generated causing degraded jitter performance

Engineering Contradiction:

Improvefrequency coverage continuityVSAvoidlimit cycles and jitter

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies the skipping principle by detecting when the DCO is approaching a frequency overlap region and temporarily bypassing those control code values. The controller skips over the problematic overlap region by adjusting the control code to jump past the boundary, thereby avoiding the limit cycle generation while maintaining frequency coverage through alternative control paths.

Inventive Principle:

Principle #21Skipping (Rushing through)

Solution Approach 2:

The patent implements preliminary action by detecting the boundary of frequency overlap regions in advance and taking preventive measures before the DCO enters the problematic region. The controller monitors the control code and predicts when an overlap region will be reached, then proactively adjusts the control signal to avoid entering the overlap region, preventing limit cycles before they occur.

Inventive Principle:

Principle #10Preliminary action

2Object-affected harmful factors

If control code is adjusted to bypass DCO frequency overlap regions, then limit cycles are reduced, but control complexity increases

Engineering Contradiction:

Improvelimit cyclesVSAvoidcontrol mechanism

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent employs feedback mechanisms where the controller continuously monitors the DCO control code and detects when it is approaching a frequency overlap region boundary. Based on this feedback information, the controller dynamically adjusts the control signal to bypass the overlap region. This closed-loop feedback approach enables automatic adaptation without requiring complex external control systems.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent introduces an intermediary control mechanism that sits between the standard PLL control loop and the DCO. This intermediary component detects overlap region boundaries and mediates the control signal by making temporary adjustments to bypass problematic regions. The intermediary acts as a buffer that simplifies the overall control architecture by handling the complexity of overlap region management in a localized manner.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12597937B2Reduce DCO frequency overlap-induced limit cycle in hybrid and digital PLLS

Publication Date: 2026.04.07 MICROCHIP TECHNOLOGY INC

AI summary

A method includes: observing that a digitally controlled oscillator (DCO) frequency is at a boundary of a DCO frequency overlap region; and bypassing at least a portion of the DCO frequency overlap region.