In-Line Distortion Cancellation Circuits With Bias-Tuned Phase Control
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Solution Overview
Problem
Existing distortion cancellation circuits for non-linear opto-electronic devices in fiber optical systems lack flexibility in tuning phase and frequency response, introduce high RF loss, and generate undesired reflections, particularly when large amounts of distortion are required, and fail to simultaneously tune both second and third order distortions effectively.
Innovation Solution
The use of Schottky or varactor diodes with adjustable bias to control the magnitude, phase, and frequency content of distortion cancellation in both pre- and post-distortion circuits, along with in-line pre-distortion circuits featuring nonlinear elements and bias inputs to generate frequency-dependent pre-distortion signals that match and oppose the distortion produced by nonlinear devices, allowing for simultaneous tuning of second and third order distortions with low insertion loss and good return loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pre-distortion or post-distortion circuits are used to cancel distortion in nonlinear devices, then the linearity of the system is improved, but the circuits introduce high RF loss and undesired reflections when large amounts of distortion are generated
Solution Approach 1:
The patent creates a copy of the distortion signal through a test path that mirrors the main signal path through the nonlinear device. This copied distortion signal is then used to generate the cancellation signal, allowing accurate distortion cancellation without requiring high-gain amplification that would introduce additional loss and reflections.
Solution Approach 2:
The patent replaces traditional high-gain amplifier-based distortion generation with a signal copying and processing approach. Instead of mechanically amplifying signals through nonlinear devices, the system uses electronic signal processing to generate the distortion cancellation signal, thereby reducing RF loss and reflections.
2Manufacturing precision
If distortion cancellation circuits are designed to correct second order distortion, then second order distortion is reduced, but undesired third order distortion is produced and both cannot be tuned simultaneously
Solution Approach 1:
The patent implements dynamic tuning capability where the distortion cancellation parameters can be adjusted in real-time. By making the system dynamic and adaptable, both second and third order distortion parameters can be independently optimized through electronic control, allowing simultaneous cancellation of multiple distortion orders without fixed circuit constraints.
Solution Approach 2:
The patent changes the approach from fixed circuit design to parameter-adjustable system. By allowing electronic adjustment of distortion cancellation parameters, the system can optimize cancellation for different distortion orders independently, enabling simultaneous reduction of both second and third order distortion through parameter optimization rather than fixed circuit topology.
3Manufacturing precision
If existing distortion circuits are used, then some degree of pre-distortion is achieved, but the circuits lack flexibility to create different frequency and phase characteristics
Solution Approach 1:
The patent creates a universal distortion cancellation system that can handle multiple types of nonlinear devices (lasers, photodiodes, RF amplifiers) and generate various frequency and phase characteristics through electronic control. The test path and signal processing architecture provide multi-functionality, allowing the same circuit to adapt to different distortion scenarios without requiring separate dedicated circuits for each application.
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 enables flexible and efficient distortion cancellation with low insertion loss and good return loss, allowing for simultaneous tuning of both second and third order distortions, effectively addressing the limitations of prior art by generating high amounts of distortion while minimizing unwanted effects.
Implementation Method 1
a Schottky or varactor diode with the bias of the diode adjusted to control the magnitude, phase and frequency content of the distortion cancellation
Data Source
AI summary
A distortion circuit is provided for correcting the distortion from a nonlinear circuit element by generating a frequency dependent signal having a sign opposite to the distortion signal produced by the nonlinear circuit and substantially the same magnitude. The distortion circuit includes an input signal and a first nonlinear device coupled to the input signal for generating a first signal and where the first nonlinear device has a first bias level. Also included is a second nonlinear device different from same first nonlinear device and coupled to the first nonlinear device for modifying the first signal to produce an output second signal, the second nonlinear device having a second bias level. A bias control means is provided for adjusting the first and said second bias levels so that the magnitude, phase and frequency of the output second signal can be adjusted.