RF Transmission Chain Predistortion for Wideband Linearity
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Solution Overview
Problem
Radiofrequency power amplifiers generate distortions due to non-linear responses, making it challenging to achieve satisfactory linearity, especially in high-modulation-order systems, and existing predistortion methods are limited by high power and bandwidth constraints, which are costly and bulkier, incompatible with low-consumption technologies like mobile phones.
Innovation Solution
A method that generates a predistortion signal with lower power and wider bandwidth than the incident signal, allowing for frequency shifting and summing to optimize the transmission chain, using digital-to-analog and analog-to-digital converters with adjusted dynamic ranges and sampling frequencies, and implemented on a silicon-germanium substrate to avoid gallium-arsenide costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional predistortion methods are used with wide passband and high incident-signal power, then linearity is improved, but device complexity and cost increase
Solution Approach 1:
The patent segments the predistortion function into two separate modules: a first module handling the incident signal with narrow passband and low power, and a second module handling the predistortion signal with wide passband and high power. This segmentation allows each module to be optimized independently, reducing overall device complexity while maintaining linearity performance.
Solution Approach 2:
The patent introduces a frequency dimension separation by shifting the predistortion signal to a different frequency range than the incident signal. The predistortion signal is frequency-shifted by at least one octave relative to the incident signal, allowing parallel processing in different frequency domains and reducing the complexity requirements for each individual module.
2Manufacturing precision
If gallium arsenide substrates are used for satisfactory linearity, then linearity is improved, but production cost increases
Solution Approach 1:
The patent changes the operating parameters of the predistortion system by separating the incident signal and predistortion signal into different power and bandwidth ranges. This parameter separation enables the use of standard silicon-based technologies for the high-power incident signal path while using lower-power, lower-cost modules for the predistortion function, eliminating the need for expensive gallium arsenide substrates.
3Manufacturing precision
If class-A amplifier design is used for linearity, then linearity is improved, but power consumption increases
Solution Approach 1:
The patent applies predistortion only to the necessary portion of the signal chain - specifically to the incident signal before it enters the power amplifier. By generating a predistortion signal that compensates for amplifier nonlinearity rather than designing the entire chain for maximum linearity, the system achieves satisfactory linearity with reduced power consumption compared to class-A designs.
4Productivity
If high modulation order systems are used for data rate, then productivity is improved, but maintaining linearity and efficiency becomes more difficult
Solution Approach 1:
The patent applies predistortion in advance before the signal enters the power amplifier. The predistortion signal is generated based on the incident signal characteristics and applied to pre-compensate for the nonlinearities that will occur during amplification. This preliminary correction enables high-modulation-order systems to maintain linearity and efficiency by preventing distortion before it occurs in the amplifier stage.
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 approach optimizes transmission chain performance, reducing production costs and bulk while maintaining high linearity, compatible with low-consumption technologies, and effective in wideband channels.
Implementation Method 1
shifting the frequency of a first signal issued from the incident signal using the shift signal so as to generate a first shifted signal
Data Source
AI summary
A transmission chain receives an incident signal to be transmitted having a first power and a first bandwidth. A first modulator frequency shifts a first signal derived from the incident signal to generate a first shifted signal at a modulation output. A power amplifier coupled to the modulation output amplifies an intermediate signal to generate an amplified output signal. A predistortion-signal-generating circuit generates, from the incident signal and from the amplified output signal in a second bandwidth that is larger than the first bandwidth, a predistortion signal having a second power lower than the first power. A second modulator frequency shifts a second signal derived from the predistortion signal to generate a second shifted signal for combination with the first shifted signal at said modulation output to produce the intermediate signal.