Dual-Path Phase Modulation for Linear RF Amplitude Control

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Solution Overview

Problem

Wireless communication systems face challenges in achieving efficient RF signal amplification with minimal distortion, particularly in portable RFID transmitters where class C amplifiers offer better efficiency but introduce amplitude distortion, limiting their use due to power consumption concerns.

Innovation Solution

A circuit that splits the RF carrier signal into two paths for phase modulation, combines them to generate an amplitude modulated output, and uses feedback loops to lock the phase and linearize the amplitude, enabling energy-efficient nonlinear amplification with reduced residual phase noise and distortion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If class C amplifiers are used for RF signal amplification, then power efficiency is improved, but amplitude distortion increases

Engineering Contradiction:

Improvepower efficiencyVSAvoidamplitude distortion

Core Design Contradiction:

Use of energy by moving objectVSManufacturing precision

Solution Approach 1:

The RF carrier signal is divided into two separate paths, each undergoing phase modulation independently. This segmentation allows nonlinear amplification in each path without direct amplitude distortion, as the amplitude modulation is synthesized by combining the phase-modulated signals rather than directly amplifying the amplitude-modulated signal.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of directly amplifying an amplitude-modulated signal (which causes distortion in class C amplifiers), the invention inverts the approach by using phase modulation on two separate paths and combining them to synthesize the amplitude-modulated output. This indirect method allows class C amplifiers to operate efficiently without introducing amplitude distortion.

Inventive Principle:

Principle #13The other way round (Inversion)

2Manufacturing precision

If class A amplifiers are used for RF signal amplification, then amplitude distortion is reduced, but power consumption increases

Engineering Contradiction:

Improveamplitude distortionVSAvoidpower consumption

Core Design Contradiction:

Manufacturing precisionVSUse of energy by moving object

Solution Approach 1:

The signal path is segmented into two separate phase-modulation paths, each capable of using efficient nonlinear amplifiers. This segmentation enables the system to achieve distortion-free output through signal combination rather than requiring linear amplification throughout the entire signal chain.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention inverts the conventional approach by not directly amplifying the amplitude-modulated signal through linear amplifiers. Instead, it uses phase modulation and signal combination to achieve amplitude modulation, allowing the use of efficient class C amplifiers while maintaining signal fidelity.

Inventive Principle:

Principle #13The other way round (Inversion)

3Use of energy by moving object

If phase modulation is applied to generate amplitude modulated signal, then power efficiency is improved, but residual phase shift increases

Engineering Contradiction:

Improvepower efficiencyVSAvoidresidual phase shift

Core Design Contradiction:

Use of energy by moving objectVSMeasurement precision

Solution Approach 1:

A feedback mechanism is employed to monitor and correct the phase relationship between the two phase-modulated paths. This feedback ensures that the residual phase shift is minimized, maintaining the precision of the synthesized amplitude-modulated signal while allowing the use of efficient nonlinear amplifiers.

Inventive Principle:

Principle #23Feedback

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 solution allows for low power consumption and undistorted output in RF transmitters, making it suitable for portable RFID readers and other wireless devices by controlling the amplitude and phase of the modulated signal to occupy a narrow frequency band, enhancing power efficiency and reducing phase noise.

Implementation Method 1

circuitry for phase modulating the carrier signal on the first path, circuitry for phase modulating the carrier signal on the second path

Methodology Applied

Scientific EffectPhase Modulation: Phase Modulation

Data Source

PatentUS7773695B2Amplitude modulator

Publication Date: 2010.08.10 NETMOMENTUM LLC

AI summary

A circuit for amplitude modulating a carrier signal includes a carrier signal input, circuitry for splitting the carrier signal into first and second paths, circuitry for phase modulating the carrier signal on the first path, circuitry for phase modulating the carrier signal on the second path, and circuitry for combining the phase modulated carrier signal on the first path with the phase modulated carrier signal on the second path for generating an amplitude modulated output signal. Feedback loops virtually eliminate residual phase shift and make the amplitude modulated output signal linearly proportional to the baseband signal.