Integrated RF Switch-Filter Network for Harmonic Rejection
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Solution Overview
Problem
RF switches using field-effect transistors (FETs) face challenges with non-linear ON-resistance, harmonics, and intermodulation distortion, which affect signal integrity and require large device sizes or multiple transistor stacks, and post-switch filtering is not optimizable for different frequency bands.
Innovation Solution
The implementation of an integrated switch-filter network with transmission lines and tank circuits configured to present open or short circuits at specific frequencies, reducing the need for series switches and minimizing harmonics and intermodulation distortion, using transmission lines of specific lengths (e.g., ¼λ or ¾λ) and LC networks to achieve improved linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional RF switches using FETs are used, then switching function is achieved, but non-linear ON-resistance, harmonics, and intermodulation distortion occur affecting signal integrity
Solution Approach 1:
The patent extracts the filtering function from a separate post-switch filter and integrates it directly into the switch architecture. Transmission lines are placed in series with switch arms and shunt arms are connected to ground, creating an integrated switch-filter network that eliminates harmonics and intermodulation distortion at their source rather than filtering them afterward.
Solution Approach 2:
The patent merges the switching function and filtering function into a single integrated network. The transmission lines and shunt arms are combined with the FET switches to form a unified structure that simultaneously performs signal routing and harmonic rejection, improving signal integrity while reducing the need for separate filtering components.
2Reliability
If large device sizes or multiple transistor stacks are used to address non-linearities, then signal integrity improves, but device complexity and size increase
Solution Approach 1:
The patent introduces transmission lines as intermediary elements between the FET switches and the signal paths. These transmission lines, with specific lengths (e.g., λ/4 at the operating frequency), act as impedance transformers that present high impedance to harmonics and intermodulation products, effectively rejecting them without requiring larger or more complex transistor configurations.
3Object-generated harmful factors
If post-switch filtering is implemented, then harmonics are reduced, but filtering is not optimizable for different frequency bands
Solution Approach 1:
The patent makes the filtering characteristics dynamic and adaptive by using transmission lines whose electrical length can be adjusted or selected based on the operating frequency band. Different transmission line lengths (e.g., λ/4, λ/2) can be used for different frequency bands, allowing the integrated switch-filter network to optimize harmonic rejection for each specific band while maintaining the same basic architecture.
4Object-generated harmful factors
If series switches are used to improve filtering, then harmonic rejection improves, but insertion loss and voltage swing across switches increase
Solution Approach 1:
The patent applies different impedance characteristics to different parts of the switch network. Transmission lines are designed with specific characteristic impedances and lengths to present high impedance locally at harmonic frequencies while maintaining low insertion loss at the fundamental frequency. This localized impedance control allows harmonic rejection without sacrificing signal transmission efficiency.
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 solution reduces ON-arm harmonic generation, minimizes voltage swing across OFF-arm switches, and improves switching performance by eliminating the need for series transistors, resulting in reduced insertion loss, increased isolation, and improved intermodulation distortion performance across multiple frequency bands.
Implementation Method 1
the first transmission line being configured to present a substantially open circuit looking into the first switch arm from the common pole node at a fundamental frequency of a signal transmitting on the second switch arm
Implementation Method 2
the tank circuit being configured to resonate at the at least one harmonic of the fundamental frequency and present a substantially short circuit to ground at the fundamental frequency
Implementation Method 3
The inductor-capacitor network may include a first shunt capacitor, a second shunt capacitor, and an inductor disposed between the first and second shunt capacitors
Data Source
AI summary
A radio-frequency module includes a switching device having first and second switch arms and a common pole node connected to both the first and second switch arms, a first shunt arm connected to the first switch arm, and a first transmission line disposed in the first switch arm between the common pole node and the first shunt arm, the first transmission line being configured to present a substantially open circuit looking into the first switch arm from the common pole node at a fundamental frequency of a signal transmitting on the second switch arm when the first switch arm is in an OFF-state and the first shunt arm is in an ON-state.