Cascaded Amplifier Feedforward Correction Without Coupler Loss
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Solution Overview
Problem
Feedforward correction systems suffer from low efficiency due to coupling loss in directional couplers, especially at low average error voltages with high peak-to-average ratios, while digital predistortion struggles with noise and complex distortion types, leading to inefficiencies and increased costs when scaling to high bandwidths and multiple antennas.
Innovation Solution
The implementation of a directional error amplifier and localized feedforward error correction between amplifier sections, using a cascade of sub-amplifiers with delay elements for interspersed error correction, allowing for optimized coupling and efficiency across varying amplitude ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If directional coupler based feedforward correction is used, then linearity is improved, but efficiency deteriorates due to coupling loss
Solution Approach 1:
The amplifier is divided into multiple parallel amplifier sections instead of using a single amplifier with feedforward correction. Each section handles a portion of the signal, eliminating the need for directional couplers and their associated coupling losses, thereby maintaining linearity while improving efficiency
Solution Approach 2:
The error correction function is extracted from the traditional feedforward architecture and distributed across multiple amplifier sections. Each section independently contributes to the corrected output signal, removing the inefficient coupler-based error extraction and injection mechanism
2Measurement precision
If error amplifier power is increased to accommodate large maximum error, then linearity is improved, but efficiency deteriorates due to high average voltage drops
Solution Approach 1:
The error correction capability is segmented across multiple amplifier sections rather than concentrated in a single error amplifier. Each section contributes incrementally to the correction, allowing the system to achieve high linearity without requiring any single amplifier to handle the full error range, thus maintaining efficiency
Solution Approach 2:
Each amplifier section is optimized for its specific local function in the correction process, contributing to the overall linearity without requiring excessive power headroom. The distributed architecture allows each component to operate in its optimal efficiency range while collectively achieving superior linearity performance
Data Source
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Figure 3a
AI summary
An amplifier circuit (200) for compensating an output signal (231) provided at an output (206) of the amplifier circuit (200) comprises a cascade of sub-amplifiers (2021-n). Each sub-amplifier of the cascade contributes to a respective part of the output signal (231). The cascade of sub-amplifiers (2021-n) comprises an end sub-amplifier (202n) and at least one preliminary sub-amplifier (2021). At least one error correction block (230) is coupled to apply feedforward error correction to an output of one of the at least one preliminary sub- amplifier (2021).