Broadband Amplifier Predistortion Circuit for Third-Order Linearity
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Solution Overview
Problem
Existing broadband amplifiers face challenges in maintaining linear amplification across a wide frequency range, particularly in CATV systems, due to second and third-order distortions, which degrade signal quality and bit error rate, and current linearization techniques are inadequate in addressing these issues, especially with newer architectures that increase RF signal levels and tilt.
Innovation Solution
The proposed solution involves a pre-distortion circuit with a diode network and input transformer, using multiple diodes and RC networks to align the phase and magnitude of distortion, reducing DC power consumption and improving broadband linearization, specifically designed for integrated circuits to minimize parasitic effects and enhance high-frequency performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the size of transistors is increased to reduce distortion, then distortion performance is improved, but power consumption increases
Solution Approach 1:
The patent applies pre-distortion by introducing a distortion compensation circuit that generates opposite-phase distortion signals before the main amplifier stage. This preliminary action cancels out the amplifier's inherent distortion, allowing the use of smaller transistors with lower power consumption while maintaining good distortion performance.
2Manufacturing precision
If newer transistor technologies are used to improve linearity, then distortion is reduced, but reliability risks increase
Solution Approach 1:
The patent introduces a distortion compensation circuit as an intermediary element that mediates between the input signal and the amplifier. This circuit generates compensation signals that cancel distortion, allowing the use of standard, reliable transistor technologies without sacrificing linearity performance.
3Manufacturing precision
If pre-distortion circuits are added to reduce distortion, then distortion cancellation is achieved, but circuit complexity increases
Solution Approach 1:
The patent merges the distortion compensation function with the existing amplifier structure by integrating the compensation circuit into the signal path. The compensation circuit shares biasing and signal routing with the main amplifier, reducing overall complexity compared to separate pre-distortion stages.
4Manufacturing precision
If RC networks are added to align phase and magnitude of distortion, then linearization performance is improved, but device complexity increases
Solution Approach 1:
The patent applies RC networks locally at critical nodes within the distortion compensation circuit to adjust phase and magnitude of distortion signals. Rather than adding complex global control mechanisms, localized RC components fine-tune the compensation signals, improving linearization with minimal added complexity.
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 effectively reduces third-order distortion and minimizes power consumption by over 40% while maintaining excellent second-order distortion control, simplifying pre-distortion design and operation across a wide bandwidth and dynamic range, suitable for modern CATV systems with high peak-to-average signal ratios.
Implementation Method 1
The linearizer circuit introduces second order distortion through the use of non-linear devices such as diodes
Implementation Method 2
an input transformer, and a linearizing diode network connected across an output of the input transformer
Implementation Method 3
a first RC network connected to a first output of the input transformer, a first linearizing diode network connected to the first RC network
Data Source
AI summary
An apparatus and method to improve broadband amplifier linearization. The present circuits make use of pre-distortion techniques to improve the 3rd order distortion of an amplifier to reduce the amount of DC power required to achieve a given system requirement. In addition, the amplifiers have broadband characteristics which lend themselves to simplified pre-distortion. A pre-distortion linearizer circuit is connected across the input terminals of an amplifier. The linearizer circuit includes multiple diodes to improve the clipping performance of the linearizer. In addition, RC circuits align the phase of the linearizer distortion to be opposite that of the amplifier.