Mixed-Signal PA Predistortion for RF Linearity and ACLR
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Solution Overview
Problem
Existing RF power amplifiers in cellular systems suffer from nonlinearity issues, leading to unwanted amplitude variations and interference with adjacent radio channels, which are difficult to address using solely analog signal processing techniques.
Innovation Solution
A mixed-signal RF power amplification system that partitions signal processing between the analog and digital domains, utilizing an in-band digital predistortion circuit and an RF power amplifier linearizer with adaptive analog predistortion, to improve linearization and minimize out-of-band emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If analog predistortion is used to linearize the power amplifier, then linearity is improved, but device complexity increases and manufacturing precision becomes more difficult
Solution Approach 1:
The patent replaces complex analog predistortion circuits with digital signal processing. The digital predistortion processor computes correction signals in the digital domain, which are then converted to analog for amplification. This substitution of digital processing for analog circuitry reduces manufacturing complexity while maintaining or improving linearity performance.
Solution Approach 2:
The patent introduces a digital-to-analog converter as an intermediary between the digital predistortion processor and the power amplifier. This intermediary allows the system to benefit from the precision and flexibility of digital processing while still providing the necessary analog signal to the amplifier, thereby reducing overall device complexity compared to purely analog solutions.
2Manufacturing precision
If digital signal processing is used to correct nonlinearity, then manufacturing precision is improved, but loss of time increases due to additional processing
Solution Approach 1:
The patent applies predistortion in advance before the signal reaches the power amplifier. The digital predistortion processor pre-computes correction signals that anticipate the amplifier's nonlinear behavior. By applying corrections beforehand rather than correcting after distortion occurs, the system minimizes processing delay while achieving the desired linearity improvement.
3Productivity
If power amplifiers operate at high power to compensate for signal attenuation, then productivity is improved, but object-generated harmful factors increase due to nonlinearity and adjacent channel interference
Solution Approach 1:
The patent applies predistortion to counteract the power amplifier's nonlinear effects before they occur. By pre-introducing opposite-phase distortion components, the system cancels out the harmful nonlinearities that would otherwise generate adjacent channel leakage. This allows the amplifier to operate at high power levels for improved productivity without generating excessive harmful interference.
Data Source
AI summary
A system for implementing linearization of a radio frequency (RF) power amplifier (PA) in a base station, as well as various component circuitry for implementing said system. By means of a smart partitioning of the signal processing for predistortion between the analog domain and the digital domain, a more linear relationship between the digital input data and the output RF signal is achieved. Linearization of the PA's output signal is obtained using a mixed-signal apparatus. The digital baseband signal enters the RF signal source. The RF signal source comprises an in-band predistortion circuit, a micro-controller and digital modulator. The output of the digital modulator is an RF signal that enters the PA module. The PA module is composed of the PA and the RF power amplifier linearizer (RFPAL). The RFPAL comprises an RF predistortion circuit, and RF signal analyzer and a microcontroller. In addition, a backward data interface connects the RF signal source with the RFPAL.