Ripple Cancellation Circuit for RF Power Amplifier

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Solution Overview

Problem

Switching power supplies used in RF amplifier circuits generate ripple signals that can violate output spectrum requirements due to their switching frequency and harmonics, which are coupled into the RF output and not effectively mitigated by existing technologies.

Innovation Solution

A ripple cancellation circuitry is introduced that uses a phase-shifted ripple cancellation signal, based on the switching frequency of the switching power supply, to cancel out the output ripple in RF amplifier circuits, incorporating phase-shifting, amplitude adjustment, and filtering circuitry to remove unrelated signals and adjust the ripple cancellation signal amplitude.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a switching power supply is used to power an RF power amplifier, then power supply efficiency is improved, but output spectrum compliance deteriorates due to ripple signals

Engineering Contradiction:

Improvepower supply efficiencyVSAvoidoutput spectrum compliance

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The ripple cancellation circuit generates a cancellation signal that is the inverse of the power supply ripple signal before it affects the RF output. This preliminary anti-action prevents the ripple from degrading output spectrum compliance while maintaining switching power supply efficiency.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

A ripple cancellation circuit is introduced as an intermediary component between the switching power supply and the RF power amplifier. This mediator processes the power supply signal to remove ripple components while preserving the efficient power delivery characteristics of the switching supply.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Speed

If switching frequency is increased to improve power supply response, then power delivery speed is improved, but ripple signal magnitude increases

Engineering Contradiction:

Improvepower delivery speedVSAvoidripple signal magnitude

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The circuit converts the harmful high-frequency ripple signal generated by fast switching into a useful cancellation signal. By detecting the ripple and generating its inverse, the circuit transforms the harmful effect of high-frequency switching into a beneficial ripple-free power delivery system.

Inventive Principle:

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

Solution Approach 2:

The ripple cancellation circuit dynamically adjusts parameters including phase shift, amplitude scaling, and frequency compensation to optimize ripple cancellation across different switching frequencies and power delivery conditions.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS7471155B1Cancelling switching power supply ripple from a radio frequency signal

Publication Date: 2008.12.30 QORVO US INC

AI summary

The present invention is ripple cancellation circuitry used with a switching power supply, which provides direct current (DC) power via a DC power amplifier (PA) signal to an RF PA final stage. The DC PA signal includes a DC component and a power supply ripple component, which is generated as a result of the switching characteristics of the switching power supply and creates an output ripple in an RF output signal from the PA final stage. The ripple cancellation circuitry substantially cancels the output ripple by adding a ripple cancellation signal having a ripple component that is phase-shifted approximately 180 degrees from the output ripple to the RF output signal. The ripple cancellation circuitry uses a switching signal that is provided by the switching power supply to generate the ripple cancellation signal.