Magnetically Coupled L-C Resonant Circuit for Wide Frequency Tuning

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Solution Overview

Problem

Monolithic L-C resonant circuits face limitations in tuning range, noise, phase accuracy, and power consumption, especially in high-frequency applications, due to the restricted variability of integrated variable capacitors and the quality factor degradation with switched inductors.

Innovation Solution

The resonance frequency of the L-C resonant circuit is adjusted through a second inductor magnetically coupled with the first inductor, which is electrically connected in parallel or series to the capacitor, by sensing the current flowing through the first inductor and forcing a scaled and/or out-of-phase replica current through the second inductor, allowing for a broader tuning range without using varactors or selection switches.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If integrated variable capacitors (MOS or PN junction varactors) are used to tune the resonance frequency, then the device can be adjusted to different frequencies, but the tuning range is limited to about 20-30% and power consumption increases

Engineering Contradiction:

Improvefrequency tuning rangeVSAvoidpower consumption

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by moving object

Solution Approach 1:

The patent replaces the electrical field-based varactor tuning mechanism with a magnetic field-based inductor coupling mechanism. By using a second inductor magnetically coupled to the first inductor through mutual inductance, the resonance frequency can be tuned over a wide range (exceeding 100%) without the power consumption penalties associated with varactor depletion regions.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the tuning parameter from capacitance variation (varactors) to inductance variation through magnetic coupling. By controlling the coupling coefficient between the two inductors, the effective inductance of the tank circuit can be varied significantly, enabling wide frequency tuning without the inherent limitations of integrated capacitors.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If selection switches are used to connect different inductors to the capacitor, then the resonance frequency can be adjusted, but the quality factor deteriorates due to the finite resistance of the switches

Engineering Contradiction:

Improvefrequency adjustabilityVSAvoidquality factor

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent introduces a second inductor as an intermediary element that magnetically couples to the first inductor. This magnetic coupling acts as a mediator to transfer energy and adjust the effective inductance without requiring direct electrical connection through switches, thereby avoiding the quality factor degradation caused by switch resistance.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If the capacitance is varied through varactors to achieve frequency tuning, then the resonance frequency can be adjusted, but noise performance deteriorates

Engineering Contradiction:

Improvefrequency tuning capabilityVSAvoidnoise

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The patent substitutes the varactor-based electrical field tuning mechanism with an inductor-based magnetic field tuning mechanism. This substitution eliminates the noise generation associated with varactor depletion region modulation and charge injection effects, providing cleaner frequency tuning suitable for sensitive RF applications.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enables a tuning range exceeding 100% from 3 GHz to 8 GHz, improving frequency adjustability while maintaining low noise and power consumption, suitable for high-frequency applications in wireless devices.

Implementation Method 1

a second inductor magnetically coupled with the first inductor that is electrically coupled in parallel (or in series) to the capacitor of the L-C tank circuit

Methodology Applied

Scientific EffectMagnetic coupling: Electromagnetic Induction

Data Source

PatentUS7649424B2Method of adjusting the resonance frequency of an L-C resonant circuit and resonant circuit

Publication Date: 2010.01.19 STMICROELECTRONICS SRL

AI summary

An L-C resonant circuit with an adjustable resonance frequency, having a capacitor and a first inductor electrically coupled together and a second inductor magnetically coupled to the first inductor. Additionally, there is a control circuit to sense a signal representing a first current flowing through the first inductor and to force through the second inductor a second current that is a replica of the first current for setting the adjustable resonance frequency of the L-C resonant circuit.