Crest Factor Reduction Circuit for Multi-Carrier Power Amplifiers
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Solution Overview
Problem
In Multi-Carrier Power Amplifier (MCPA) communication transmission, high crest factor signals lead to high intermodulation distortion (IMD) and increased Adjacent Channel Power Ratio (ACPR), reducing amplifier efficiency and increasing out-of-band emissions, while existing methods to reduce crest factor either decrease efficiency or increase complexity and cost.
Innovation Solution
A system comprising a peak amplitude suppressor and an intermodulation distortion rejection filter, where the peak amplitude suppressor computes and applies a gain factor to the input signal to reduce peak amplitudes, and the IMD rejection filter, implemented with bandpass or finite impulse response filters, selectively suppresses or rejects IMD components to maintain low ACPR and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the transmit signal level is decreased to maintain low ACPR without linearization techniques, then ACPR is improved, but amplifier efficiency deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-processing the input signal through a peak amplitude suppressor before amplification. The suppressor identifies and reduces peak amplitudes in advance, allowing the power amplifier to operate at higher efficiency levels without generating excessive ACPR, thus resolving the contradiction between ACPR performance and amplifier efficiency
Solution Approach 2:
The peak amplitude suppressor acts as an intermediary component between the signal source and the power amplifier. It modifies the signal characteristics (reducing crest factor) before the signal enters the amplifier, enabling the amplifier to operate efficiently while maintaining low ACPR, thus mediating between the conflicting requirements
2Object-affected harmful factors
If amplitude limiting is applied to reduce crest factor, then crest factor is improved, but out of band emissions increase and ACPR deteriorates
Solution Approach 1:
The patent applies local quality by selectively reducing only the peak amplitudes of the signal while preserving the overall signal structure and spectral characteristics. The peak amplitude suppressor targets specific high-amplitude portions of the signal for reduction, rather than uniformly limiting the entire signal, thus reducing crest factor without significantly increasing out of band emissions or ACPR
Solution Approach 2:
The patent applies partial action by applying amplitude suppression only when and where peak amplitudes exceed a certain threshold, rather than continuously limiting the entire signal. This selective approach reduces the crest factor effect while minimizing the generation of out of band emissions that would result from more aggressive amplitude limiting
3Object-affected harmful factors
If conventional amplitude limiting is used to reduce crest factor, then crest factor is improved, but system complexity increases
Solution Approach 1:
The patent replaces complex mechanical or hardware-based amplitude limiting systems with an electronic signal processing approach. The peak amplitude suppressor uses electronic computation and control to identify and reduce peak amplitudes, substituting simpler electronic components for more complex traditional amplitude limiting hardware, thus reducing overall system complexity while maintaining crest factor reduction effectiveness
Data Source
AI summary
A crest reduction system and method. The inventive system includes a first circuit for suppressing peak amplitudes of an input signal and providing a peak amplitude suppressed signal in response thereto and a second circuit coupled to the first circuit for rejecting intermodulation distortion in the amplitude suppressed signal. In the illustrative implementation, the first circuit is a peak amplitude suppressor having circuitry for computing an amplitude of the input signal and for computing a gain factor for the input signal in response thereto. In the best mode, the gain factor is obtained from a lookup table. The peak amplitude suppressor further includes a multiplier for applying the gain factor to the input signal. In the illustrative embodiment, the second circuit includes a plurality of bandpass filters and a summer for combining the outputs thereof.