Switchable RF Filter Structure for Self-Interference Cancellation

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Solution Overview

Problem

Existing RF devices face challenges in achieving compact, cost-effective, and high-quality filtering solutions, particularly in multi-frequency band operations, due to the limitations of SAW and BAW filters.

Innovation Solution

A circuit design for self-interference cancellation in RF transceivers, comprising a first circuit element with inductors on one substrate and a second circuit element with capacitors and switching devices on another substrate, controlled by a unit to adapt the signal path for interference cancellation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If SAW and BAW filters are used for RF filtering, then filtering performance is improved, but device volume and cost increase

Engineering Contradiction:

Improvefiltering performanceVSAvoiddevice volume

Core Design Contradiction:

ReliabilityVSVolume of stationary object

Solution Approach 1:

The patent combines multiple filter functions (transmit filter, receive filter, and self-interference cancellation filter) into a single integrated filter structure. This merging of previously separate SAW/BAW filter components into one unified device reduces the overall device volume while maintaining the required filtering performance across multiple frequency bands.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The integrated filter structure is designed to perform multiple functions simultaneously: it acts as a transmit filter, receive filter, and self-interference cancellation filter across different frequency bands. This multi-functionality eliminates the need for separate dedicated filters for each function and frequency band, thereby reducing device volume and component count.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If multiple SAW or BAW filters are used for multi-frequency band operation, then frequency coverage is improved, but cost and space usage increase

Engineering Contradiction:

Improvefrequency coverageVSAvoidnumber of filters

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The filter incorporates switchable components that allow dynamic reconfiguration of the filter response to adapt to different frequency bands and operational modes. This dynamic capability enables a single filter structure to replace multiple fixed-frequency filters, reducing both the number of components and overall complexity.

Inventive Principle:

Principle #15Dynamics

3Reliability

If inductive components are manufactured with high quality factor, then signal quality is improved, but manufacturing difficulty increases

Engineering Contradiction:

Improvesignal qualityVSAvoidmanufacturing difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces traditional discrete inductive components with planar inductors fabricated using standard printed circuit board (PCB) metallisation techniques. This substitution of mechanical/wound inductors with planar trace-based inductors maintains acceptable signal quality while dramatically simplifying the manufacturing process and enabling integration with other circuit elements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent optimizes the geometric parameters of the planar inductors (trace width, trace spacing, number of turns, loop area) to achieve the required inductance values and quality factors using standard PCB fabrication capabilities. By carefully controlling these geometric parameters, the design achieves acceptable signal quality without requiring complex manufacturing processes.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20250070757A1Filter structures

Publication Date: 2025.02.27 FOREFRONT RF LTD

AI summary

A circuit for providing self-interference cancellation in a radio transceiver, the circuit comprising: a first circuit element provided on a first substrate and comprising one or more inductors; a second circuit element provided on a second substrate and comprising one or more capacitors; at least one switching device provided on the second substrate, the switching device being capable of switching one or more of the inductors and the capacitors into or out of a signal path; and a control unit adapted to control the switching device so as to adapt the response of the signal path to perform self-interference cancellation.