Tunable Inductor With Phase Shifting For LC VCOs

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Solution Overview

Problem

The tuning range of LC-tank oscillators is limited, making it difficult to cover multiple frequency standards in wireline communication, and existing methods to increase this range, such as using varactor banks, are hindered by parasitic effects that degrade the quality factor.

Innovation Solution

A tunable inductor design featuring a primary coil in parallel with isolated secondary coils and phase shifting devices between open-circuited ports of the secondary coils, allowing for fine-tuning of mutual inductance and overall inductance through active and passive coupling structures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If more varactor banks are used to increase the tuning range of LC-tanks, then the capacitance variation increases, but capacitive parasitics decrease the Cmax/Cmin-ratio and resistive parasitics degrade the quality factor

Engineering Contradiction:

Improvetuning rangeVSAvoidquality factor

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent replaces the mechanical/electrical switching of multiple varactor banks with a phase-shifting mechanism that controls the coupling between primary and secondary coils. This substitution eliminates the need for multiple discrete capacitor banks and their associated parasitic elements, achieving wide tuning range without quality factor degradation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent employs a composite inductor structure combining primary and secondary coils with coupled magnetic fields. This composite structure enables continuous inductance tuning through phase control while maintaining high quality factor, avoiding the parasitic limitations of composite varactor bank approaches.

Inventive Principle:

Principle #40Composite materials

2Adaptability or versatility

If the number of varactor banks is increased to extend frequency ranges, then the capacitance variation increases, but the resistive parasitics degrade the quality factor disproportionately due to longer wiring traces

Engineering Contradiction:

Improvefrequency range coverageVSAvoidresistive losses

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The patent merges the functions of multiple varactor banks into a single integrated inductor structure with coupled primary and secondary coils. The phase-shifting mechanism controls the effective inductance by adjusting the coupling between coils, eliminating the need for multiple separate capacitor banks and their associated wiring traces and resistive losses.

Inventive Principle:

Principle #5Merging (Combining)

3Adaptability or versatility

If inductor coils are switched to perform tuning at higher frequencies, then the tuning capability improves, but the quality factor degrades due to resistive losses of closed switches

Engineering Contradiction:

Improvehigh frequency tuning capabilityVSAvoidquality factor

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent implements dynamic tuning by controlling the phase relationship between primary and secondary coils rather than using static switch connections. The phase-shifting mechanism continuously adjusts the coupling between coils, enabling high-frequency operation without the quality factor degradation associated with switch resistance in traditional switched inductor configurations.

Inventive Principle:

Principle #15Dynamics

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 design achieves a wide tuning range with improved granularity and reduced inductance step size, maintaining a high quality factor by minimizing resistive losses and parasitic effects, thus enhancing the performance of LC VCOs across various frequencies.

Implementation Method 1

at least one phase shifting device arranged between open-circuited ports of at least one secondary coil

Methodology Applied

Scientific EffectPhase shifting:

Implementation Method 2

The inductor comprises a primary coil coaxially arranged and operated in parallel with one or more isolated secondary coils

Methodology Applied

Scientific EffectMutual inductance: Electromagnetic Induction

Data Source

PatentUS8717138B2Inductor combining primary and secondary coils with phase shifting

Publication Date: 2014.05.06 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

An inductor including a primary coil coaxially arranged and operated in parallel with isolated secondary coils each including at least one loop winding with two open-circuited ports. At least one phase shifting device is arranged between open-circuited ports of at least one secondary coil. A method to operate an inductor by combining primary and secondary coils with phase shifting devices to get a wide tuning range is also provided. The method includes the step of phase shifting open-circuited ports of at least one secondary coil.