Subharmonic Switching Power Amplifier for Efficient Power Back-Off

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Solution Overview

Problem

Power amplifiers (PAs) face significant efficiency degradation when operating in the power back-off (PBO) region, which is critical for achieving high average power efficiency in wireless communication systems due to high peak-to-average-power ratios (PAPRs) in modern wireless communication systems, and existing techniques like envelope-tracking, Doherty, and load modulation face design challenges such as large bandwidth requirements and complexity.

Innovation Solution

The implementation of subharmonic switching (SHS) in digital power amplifiers, where the PA switches at a subharmonic component of the carrier frequency, reducing power loss and maintaining high efficiency in the PBO region, combined with techniques like class-G operation and phase-interleaved architectures to enhance efficiency peaks and cancel unwanted subharmonic components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the PA operates at peak power, then the efficiency is highest, but the output power cannot be scaled back for PBO operation

Engineering Contradiction:

Improvepower efficiencyVSAvoidoutput power flexibility

Core Design Contradiction:

Loss of energyVSPower

Solution Approach 1:

The PA toggles dynamically between different operating states (ON/OFF) at subharmonic frequencies, allowing the output power to be scaled back while maintaining high efficiency through periodic operation rather than continuous operation at fixed power levels

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The PA employs periodic toggling at subharmonic frequencies (e.g., f/2, f/3) to achieve power back-off while maintaining efficiency, using periodic ON/OFF cycles to reduce average power consumption while preserving peak efficiency during active periods

Inventive Principle:

Principle #19Periodic action

2Loss of energy

If the PA is toggled at subharmonic frequency, then power loss is reduced and efficiency is improved in PBO region, but the output power magnitude decreases

Engineering Contradiction:

Improvepower lossVSAvoidoutput power magnitude

Core Design Contradiction:

Loss of energyVSPower

Solution Approach 1:

The invention changes the toggling frequency parameter from the fundamental carrier frequency to subharmonic frequencies (f/2, f/3, etc.), which reduces switching losses and improves efficiency in the PBO region while accepting reduced output power magnitude as a trade-off for better efficiency

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If envelope-tracking PA is used, then efficiency within deep PBO region is very high, but supply modulators with large bandwidths and dynamic ranges are required

Engineering Contradiction:

Improveefficiency in deep PBO regionVSAvoidsupply modulator bandwidth and dynamic range

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The subharmonic switching technique uses simple ON/OFF toggling at reduced frequencies instead of complex high-bandwidth supply modulators, achieving deep PBO efficiency with simpler, lower-bandwidth control circuitry that does not require large dynamic range modulators

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

4Loss of energy

If Doherty PA is used, then additional efficiency peaks in PBO region are provided, but large area is required for the power combiner

Engineering Contradiction:

Improveefficiency peaks in PBO regionVSAvoidpower combiner area

Core Design Contradiction:

Loss of energyVSArea of stationary object

Solution Approach 1:

The subharmonic switching technique extracts the efficiency enhancement function from the complex Doherty power combiner structure and implements it through simple frequency division and periodic toggling, achieving multiple efficiency peaks without requiring large-area power combining networks

Inventive Principle:

Principle #2Taking out (Extraction)

5Adaptability or versatility

If outphasing-based PA is used, then larger bandwidth is achieved, but mismatch of the two PAs must be dealt with for good linearity

Engineering Contradiction:

ImprovebandwidthVSAvoidPA matching complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The PA is segmented into multiple parallel units that toggle at different subharmonic frequencies, with a frequency divider segmenting the carrier frequency into subharmonics and a MUX selecting the appropriate subharmonic for each PA unit, reducing matching complexity while maintaining bandwidth

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS11159126B2Sub-harmonic switching power amplifier

Publication Date: 2021.10.26 UNIV OF SOUTHERN CALIFORNIA

AI summary

A subharmonic switching digital power amplifier system includes a power amplifier core that includes at least one power amplifier operable in a power back-off region and a power supply providing at least one operating voltage to the power amplifier. Characteristically, the power amplifier is toggled at a subharmonic component of a carrier frequency (Fc) to achieve power back-off wherein the power amplifier is operated in a voltage mode or current mode driver. Multi-subharmonics can be used to further enhance the power back-off efficiency. A switching digital power amplifier system employing phase interleaving is also provided.