LNA Notch Filter for TX Harmonic Coupling

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Solution Overview

Problem

The increasing complexity of RF devices leads to potential coupling of RF frequency components from the transmit side of an RF frontend stage operating at one frequency band to the receive side operating at a different frequency band, which can degrade the performance of the receive path.

Innovation Solution

A multi-band multi-channel RF frontend circuit is designed with a notch filter coupled at the output of the first receive low noise amplifier (LNA), featuring a notch at a harmonic of the first frequency within the first band, thereby reducing harmonic coupling to the second receive LNA.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multiple frequency bands and complex modulation schemes are implemented to improve data throughput and adaptability, then the functionality and performance of the RF device is improved, but the device complexity increases leading to frequency coupling between transmit and receive paths

Engineering Contradiction:

Improvefrequency band supportVSAvoidRF frontend complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The RF frontend is divided into separate processing blocks for different frequency bands (first processing block for first band, second processing block for second band), each with dedicated amplifiers and filters. This segmentation isolates the signal paths and prevents frequency coupling between bands while maintaining multi-band functionality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A notch filter is introduced as an intermediary component at the output of the first receive LNA to specifically attenuate harmonic frequencies that could couple into the second band receive path. This mediator selectively removes harmful frequency components without affecting the desired signal.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If transmit path and receive path share common components to reduce device complexity, then the device complexity is reduced, but frequency coupling occurs degrading receive performance

Engineering Contradiction:

Improvefrontend stage complexityVSAvoidreceive path performance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The frontend stage is segmented into distinct first and second processing blocks for different frequency bands, with separate amplifiers (PA1, LNA1 for first band; LNA2 for second band) and filters. This segmentation maintains performance isolation while using a shared RF frontend architecture.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The harmful harmonic components are extracted and removed by the notch filter at the output of the first receive LNA, separating the useful signal from the harmful frequency components that could cause coupling to the second band.

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If harmonics of first band frequency are present in the receive path to maintain signal integrity, then the signal processing is improved, but the harmonics couple to second band receive path causing desensitization

Engineering Contradiction:

Improvesignal processing qualityVSAvoidharmonic coupling

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The notch filter converts the harmful harmonic components into a beneficial filtering action by selectively attenuating these harmonics at the output of the first receive LNA, preventing them from coupling into the second band receive path while preserving the main signal integrity.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The notch filter serves as an intermediary component that specifically targets and removes harmonic frequencies (notches at harmonic of first frequency) from the signal path, acting as a protective barrier between the first band processing and second band receiving.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

The implementation of the notch filter effectively reduces the level of harmonics coupled from the first band to the second band, enhancing the performance of the receive path by minimizing desensitization and noise figure degradation.

Implementation Method 1

a notch filter coupled at an output of the first receive LNA, wherein the notch filter comprises a notch at a harmonic of a first frequency

Methodology Applied

Scientific EffectFrequency selective filtering: Filter (electronic)

Data Source

PatentUS20250105996A1LNA with TX harmonic filter

Publication Date: 2025.03.27 PSEMI CORP

AI summary

Methods and devices for reducing coupling of RF frequency components between different bands of an RF system are presented. According to one aspect, a notch filter having a notch centered at a harmonic of a fundamental frequency of a first band transmit side is coupled to an output of an LNA of the first band. According to another aspect, the harmonic is a second harmonic, a third harmonic or higher order harmonics. According to another aspect, the notch filter includes a plurality of notches at respective plurality of harmonics. According to a further aspect, the notch has an attenuation of 30 dB or greater at the second harmonic and 10 dB or greater at the third harmonic. Further included is a method for reducing coupling of harmonics of signals transmitted in the first band into a receive path of the second band, thereby increasing noise figure/sensitivity performances of the receive path.