RF Bitstream Combiner Using Phase Cancellation for Image Rejection

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Solution Overview

Problem

Digital RF systems face inefficiencies when low sampling rates cause image components of desired carrier signals to appear in or near the desired signal band, necessitating expensive filtering to remove undesired image components.

Innovation Solution

A circuit and electronic system that combine multiple RF signals by generating digital bitstreams with a ninety-degree phase difference, using directional couplers and Hilbert bandpass filters to suppress image components without the need for filtering, leveraging quadrature hybrid couplers for phase cancellation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If low sampling rates are used in digital RF systems, then system efficiency is improved, but image components appear in or near the desired signal band requiring expensive filtering

Engineering Contradiction:

Improvesystem efficiencyVSAvoidfiltering complexity

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The patent converts the harmful image components generated by low sampling rate operation into beneficial phase-cancelled signals. By processing the image components through quadrature modulators with ninety-degree phase shifted local oscillators and combining them in a directional coupler, the image components from different paths cancel each other out, transforming what was previously a harmful artifact into a useful feature that enables low sampling rate operation without requiring expensive filters

Inventive Principle:

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

Solution Approach 2:

The patent applies preliminary anti-action by pre-processing the image components before they become harmful interference. The image components are generated intentionally at low sampling rates, then immediately processed through quadrature modulation and directional coupling arrangements that create phase-inverted copies of these image components, which are then combined to cancel them out before they can interfere with the desired signal

Inventive Principle:

Principle #9Preliminary anti-action

2Reliability

If filtering is used to remove image components, then signal purity is improved, but power loss and cost increase

Engineering Contradiction:

Improvesignal purityVSAvoidpower loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent substitutes mechanical/physical filtering systems with an electronic signal processing system. Instead of using lossy reflective or absorptive filters that physically remove image components through reflection or absorption, the patent uses quadrature modulators and directional couplers to electronically cancel image components through phase interference, replacing a mechanical filtering approach with an electronic cancellation approach that avoids power loss

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 effectively attenuates image components, enhancing signal efficiency by eliminating the requirement for costly filtering while maintaining power gain, thus improving the signal-to-noise ratio without power loss.

Implementation Method 1

combining two or more RF signals in such a manner that image components associated with the RF signals are suppressed without a need for filtering

Methodology Applied

Scientific EffectPhase cancellation: Interference

Implementation Method 2

leveraging quadrature hybrid couplers for phase cancellation

Methodology Applied

Scientific EffectQuadrature hybrid coupling:

Implementation Method 3

using directional couplers and Hilbert bandpass filters to suppress image components

Methodology Applied

Scientific EffectBandpass filtering: Filter (electronic)

Data Source

PatentUS9673859B2Radio frequency bitstream generator and combiner providing image rejection

Publication Date: 2017.06.06 AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE LTD

AI summary

A circuit for combining analog signals includes first and second bitstream generators and a directional coupled connected therewith. The first bitstream generator receives a first analog signal and generates a first digital bitstream as a function thereof. The second bitstream generator receives a second analog signal and generates a second digital bitstream as a function thereof. The first and second bitstream generators are configured to maintain a ninety-degree phase difference between the first and second digital bitstreams. The directional coupler receives, at a first port, the first digital bitstream, and receives, at a second port, the second digital bitstream. The directional coupler includes a third port that is terminated, and a fourth port which generates a first output signal indicative of a combination of the first and second digital bitstreams in a manner that an image component is suppressed without a need for filtering.