Wideband RF Amplifier Staging for Second-Order Distortion Cancellation
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Solution Overview
Problem
Existing RF amplifiers introduce second-order harmonic distortion, which is difficult to remove in wideband systems without additional parallel amplifiers, as conventional methods are not always feasible or convenient.
Innovation Solution
A system comprising a first non-linear circuit stage, a linear circuit stage, and a second non-linear circuit stage are coupled in series, where the linear stage inverts and attenuates the signal to cancel out second-order distortion, maintaining unity gain and reducing unwanted second-order components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a parallel, balanced amplifier configuration is used to reduce second-order distortion, then second-order harmonic distortion is reduced, but device complexity increases due to requiring additional amplifiers
Solution Approach 1:
The amplifier is divided into three distinct circuit stages: a first non-linear stage, a linear middle stage, and a second non-linear stage. This segmentation allows each stage to perform a specific function in the distortion cancellation process, reducing overall second-order distortion without requiring parallel amplifier configurations.
Solution Approach 2:
The linear circuit stage inverts the signal from the first non-linear stage before passing it to the second non-linear stage. This inversion causes the second-order distortion products generated by both non-linear stages to cancel each other out, achieving distortion reduction through inverse signal processing rather than parallel cancellation.
2Object-generated harmful factors
If filtering is used to remove second-order distortion, then second-order harmonics are removed, but this approach is ineffective when instantaneous bandwidth exceeds an octave causing in-band distortion
Solution Approach 1:
The invention converts the harmful second-order distortion products into beneficial cancellation signals. By processing the inverted signal through a second non-linear stage with similar characteristics, the distortion products are regenerated with opposite polarity, causing them to cancel each other out and leaving a cleaned output signal.
3Device complexity
If conventional single-stage amplifiers are used, then device complexity is low, but second-order non-linear distortion is introduced in the output signal
Solution Approach 1:
The invention changes the operational parameters of the amplifier by introducing a linear attenuation stage with gain less than unity between two non-linear stages. This parameter change allows the system to operate in a regime where distortion cancellation occurs, transforming the amplifier's transfer function to eliminate second-order terms while maintaining useful signal gain.
Data Source
Figure 1A~1B
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Figure 3
AI summary
A system has a plurality of non-linear circuit stages and an intervening linear circuit stage. An input signal is provided to a first non-linear circuit stage, and from the first non-linear circuit stage, to the linear circuit stage. The first non-linear circuit stage applies a second-order distortion to the input signal and provides the resulting signal to the linear circuit stage. The resulting signal that is output from the linear circuit stage is inverted with respect to the input signal and suitably linearly processed (attenuated or amplified). This signal is then provided to a second non-linear circuit that applies a second-order distortion and outputs a signal that has an overall reduction in second-order distortion.