Power Amplifier Bandpass Filtering for Sideband Loss Reduction
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Solution Overview
Problem
High peak to average power ratio (PAPR) signaling schemes in modern communication systems, such as LTE and WiMAX, consume more power due to less efficient operation of power amplifiers, which is a challenge in reducing power consumption and achieving compact, cost-effective RF transmission systems.
Innovation Solution
A power amplifier system that includes a bandpass filter with a lower input impedance at in-band frequencies than out-of-band frequencies, coupled with a predistorted pulse width modulated waveform to reduce power dissipation in sidebands, enabling more efficient operation by attenuating sidebands and optimizing power consumption based on the state of the pulse width modulated signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high PAPR signaling schemes (LTE, WiMAX) are used to increase bandwidth efficiency, then data transmission capability is improved, but power amplifier efficiency deteriorates due to operation in back-off condition
Solution Approach 1:
The patent applies parameter changes by modifying the impedance characteristics of the output filter across different frequency bands. The filter is designed with frequency-dependent impedance: low impedance at the carrier frequency to maximize power transfer, and high impedance at sideband frequencies to minimize power dissipation. This parameter variation resolves the contradiction by allowing the PA to operate efficiently with high PAPR signals.
Solution Approach 2:
The patent implements local quality by creating different impedance conditions at different frequency locations. The output filter provides locally optimized impedance matching: low impedance locally at the carrier frequency for efficient power delivery, and high impedance locally at sideband frequencies to prevent power loss. This spatial-frequency differentiation resolves the efficiency-bandwidth tradeoff.
2Use of energy by moving object
If power amplifier is operated closer to compression for power efficient signaling (GMSK), then power efficiency is improved, but bandwidth efficiency deteriorates compared to high PAPR schemes
Solution Approach 1:
The patent enables the PA to operate in a compressed state (higher efficiency) while maintaining bandwidth efficiency by dynamically changing the output filter impedance parameters. The frequency-selective impedance transformation allows compressed operation to be sustained without the traditional penalty of reduced bandwidth capability.
3Use of energy by moving object
If output filter has low impedance at carrier frequency for efficient power transfer, then power amplifier efficiency is improved, but power dissipation in sidebands increases
Solution Approach 1:
The patent resolves this contradiction through local quality by implementing frequency-dependent impedance in the output filter. The filter presents low impedance locally at the carrier frequency to maximize power transfer efficiency, while simultaneously presenting high impedance locally at sideband frequencies to minimize power dissipation. This localized impedance optimization at different frequency positions resolves the energy transfer vs. energy loss contradiction.
Solution Approach 2:
The output filter parameters are changed across the frequency spectrum: impedance magnitude varies from low at carrier frequency to high at sideband frequencies. This parameter transformation across different frequency domains simultaneously achieves efficient power transfer and reduced sideband power dissipation.
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 configuration significantly reduces power dissipation in sidebands, leading to more efficient power amplifier operation, improved coding efficiency, and reduced power consumption, especially during the RF off-period, thereby enhancing overall amplifier efficiency.
Implementation Method 1
The bandpass filter has a lower input impedance at an in-band center frequency than at out-of-band frequencies, and the first amplifier is configured to receive a pulse width modulated waveform filtered according to a first transfer function that attenuates sidebands of the pulse width modulated waveform
Data Source
AI summary
In accordance with an embodiment, a system includes a first amplifier and a first bandpass filter having an input coupled in series with an output of the first amplifier, and an output configured to be coupled to a load. The bandpass filter has a lower input impedance at an in-band center frequency than at out-of-band frequencies, and the first amplifier is configured to receive a pulse width modulated waveform filtered according to a first transfer function that attenuates sidebands of the pulse width modulated waveform.