Multi-Path VCO with Shared Varactor for Stable PLL Control

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Solution Overview

Problem

Conventional dual-path voltage-controlled oscillators (VCOs) face challenges in maintaining stable phase-locked loop stability and electromagnetic interference suppression due to size disparities and mismatched DC bias in separate varactors across different paths, especially under process, voltage, and temperature variations.

Innovation Solution

A multi-path VCO design that uses a single varactor controlled by both integral and proportional paths through a control voltage generator circuit, employing time-division multiplexing of control voltages from these paths to maintain stable DC bias and reduce electromagnetic interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If separate varactors are employed for I-path and P-path in conventional dual-path VCO design, then bandwidth control and frequency control can be implemented independently, but size disparity between the two varactors causes bad matching and they cannot track the same DC bias under PVT variation

Engineering Contradiction:

Improveindependent bandwidth and frequency controlVSAvoidmatching accuracy and DC bias tracking

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent merges the I-path and P-path control functions into a single shared varactor, eliminating size disparity and DC bias tracking issues. The control voltage generator circuit combines both control voltages through addition, allowing independent control signals to be integrated into a unified control mechanism that maintains accurate matching under PVT variation.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The single varactor serves multiple functions by being controlled through a composite control voltage that incorporates both I-path (frequency control) and P-path (bandwidth control) components. This universal control approach allows one varactor to perform what previously required two separate varactors, while maintaining consistent electrical characteristics.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Object-affected harmful factors

If a large I-path gain Ki is used to achieve better EM suppression, then electromagnetic interference suppression is improved, but PLL loop stability deteriorates

Engineering Contradiction:

Improveelectromagnetic interference suppressionVSAvoidPLL loop stability

Core Design Contradiction:

Object-affected harmful factorsVSStability of the object's composition

Solution Approach 1:

The patent changes the control approach by introducing a proportional path control voltage component that is added to the integral path control voltage. This parameter modification allows the system to achieve EM suppression benefits of high Ki while maintaining loop stability through the proportional control contribution, effectively decoupling the trade-off between EM suppression and stability.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12261607B2Multi-path voltage-controlled oscillator with same varactor controlled by inputs from different paths and associated method

Publication Date: 2025.03.25 MEDIATEK INC

AI summary

A multi-path voltage-controlled oscillator (VCO) includes a VCO core circuit and a control voltage generator circuit. The VCO core circuit includes a varactor that has a control node for receiving a control voltage. The control voltage generator circuit receives at least one proportional path (P-path) control input and an integral path (I-path) control input, and generates and outputs the control voltage to the control node of the varactor according to the at least one P-path control input and the I-path control input.