RF Front End Input Filtering for Low-Interference Power Amplifiers

Solution Overview

Problem

Existing radio frequency front end modules in access points require high-power consumption and inefficient bandpass filters to reduce radio interference, leading to poor DC/thermal efficiency and performance.

Innovation Solution

The access point filters the input to a non-linear power amplifier using a bandpass filter, eliminating the need for filters on the output of the power amplifier, and operates the power amplifier at a high biasing condition to reduce non-linearity and harmonics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If bandpass filters are placed at the output of power amplifiers to reduce radio interference, then radio frequency leakage and interference between radios are reduced, but power consumption increases, DC/thermal efficiency deteriorates, and insertion loss increases

Engineering Contradiction:

Improveradio interferenceVSAvoidpower consumption

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

The patent inverts the conventional filter placement from output to input of the power amplifier. By placing the bandpass filter before the power amplifier, the system achieves interference reduction without the penalties of high power consumption and poor efficiency associated with output filtering. This inversion fundamentally changes where the filtering action occurs in the signal chain.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The filter performs preliminary filtering of the RF signal before it reaches the power amplifier. By pre-filtering the input signal to remove out-of-band components and reduce non-linearity beforehand, the power amplifier operates more efficiently with reduced spectral regrowth, eliminating the need for post-amplification filtering that would consume excessive power.

Inventive Principle:

Principle #10Preliminary action

2Object-affected harmful factors

If bandpass filters operate at high operating point to filter power amplifier outputs, then radio frequency leakage is reduced, but insertion loss increases and performance deteriorates

Engineering Contradiction:

Improveradio frequency leakageVSAvoidperformance

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent inverts the conventional filter placement from output to input of the power amplifier. By placing the bandpass filter before the power amplifier, the system achieves interference reduction without the penalties of high power consumption and poor efficiency associated with output filtering. This inversion fundamentally changes where the filtering action occurs in the signal chain.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The filter performs preliminary filtering of the RF signal before it reaches the power amplifier. By pre-filtering the input signal to remove out-of-band components and reduce non-linearity beforehand, the power amplifier operates more efficiently with reduced spectral regrowth, eliminating the need for post-amplification filtering that would consume excessive power.

Inventive Principle:

Principle #10Preliminary action

3Object-affected harmful factors

If multiple switchable bandpass filters are used in front end modules, then coexistence problems between simultaneous radios are reduced, but device complexity and cost increase

Engineering Contradiction:

Improvecoexistence problemsVSAvoidfront end module complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent changes the operating parameters of a single bandpass filter dynamically. Instead of using multiple physical filters, the system adjusts the bandpass filter's center frequency and bandwidth parameters to match different radio channels and modes (e.g., 2.4 GHz vs 5 GHz, different Wi-Fi channels), achieving multi-radio coexistence with a single filter through parameter reconfiguration.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The single bandpass filter is designed to serve multiple functions across different radio operations. By making the filter tunable and reconfigurable, it can support multiple frequency bands, channels, and radio modes, replacing what would traditionally require multiple dedicated filters, thereby reducing device complexity while maintaining coexistence performance.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 reduces power consumption, improves DC/thermal efficiency, and enhances radio performance by minimizing interference and spectral regrowth.

Implementation Method 1

The bandpass filter filters the electrical signal from the transmitter to produce a filtered signal

Methodology Applied

Scientific EffectBandpass filtering: Filter (electronic)

Implementation Method 2

The non-linear power amplifier amplifies the filtered signal from the bandpass filter to produce an amplified signal

Methodology Applied

Scientific EffectPower amplification: Magnetic Amplifier

Data Source

PatentUS20260066931A1Radio frequency front end architecture

Publication Date: 2026.03.05 CISCO TECHNOLOGY INC

AI summary

The present disclosure describes an access point that filters the input to power amplifiers of a front end module. The access point includes a transmitter, a bandpass filter, a non-linear power amplifier, and an antenna. The transmitter produces an electrical signal. The bandpass filter filters the electrical signal from the transmitter to produce a filtered signal. The non-linear power amplifier amplifies the filtered signal from the bandpass filter to produce an amplified signal. The antenna transmits a first wireless signal based on the amplified signal.