Wideband RF Amplifier Staging for Second-Order Distortion Cancellation
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Solution Overview
Problem
Conventional RF amplifiers introduce second-order harmonic distortion, which is difficult to remove in wideband systems without additional parallel amplifiers, as filtering is inappropriate when the instantaneous bandwidth is greater than an octave.
Innovation Solution
A series configuration of non-linear and linear circuit stages is used, where the first non-linear stage adds a second-order component, the linear stage inverts and attenuates it, and the second non-linear stage cancels the distortion, resulting in an output signal with substantially unity gain and reduced second-order distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If filtering is used to remove second order distortion, then distortion is reduced, but filtering is inappropriate when the instantaneous bandwidth is greater than an octave
Solution Approach 1:
The amplifier is segmented into multiple stages: a first non-linear stage that introduces second-order distortion, a linear stage that inverts and attenuates the signal, and a second non-linear stage that cancels the distortion. This segmentation allows distortion cancellation without requiring external filtering, making the solution applicable to wideband systems where filtering would be inappropriate.
Solution Approach 2:
The linear stage performs preliminary anti-action by inverting the signal before it enters the second non-linear stage. This inversion causes the second non-linear stage to generate distortion products that are equal in magnitude but opposite in phase to those from the first non-linear stage, thereby canceling the distortion before the output signal is produced.
2Object-affected harmful factors
If multiple amplifiers are used in parallel, anti-phase configuration, then second order distortion is reduced, but device complexity increases
Solution Approach 1:
The invention merges multiple functions into a single amplifier chain: distortion introduction, signal inversion, and distortion cancellation are all performed within one sequential path rather than requiring separate parallel amplifiers. The linear stage serves dual purposes of both inversion and providing the correct phase relationship for distortion cancellation, eliminating the need for additional parallel amplifier paths.
Solution Approach 2:
The linear stage performs multiple functions: it inverts the signal from the first non-linear stage, attenuates the signal to the appropriate level, and establishes the correct phase relationship for the second non-linear stage. This multi-functionality reduces the overall system complexity compared to using separate dedicated components for each function.
3Device complexity
If a single amplifier is used, then device complexity is reduced, but second order distortion is not cancelled
Solution Approach 1:
The invention changes key parameters of the signal as it passes through each stage: the first non-linear stage changes the amplitude parameter while introducing distortion, the linear stage changes the phase parameter by inverting the signal, and the second non-linear stage changes both amplitude and phase parameters to cancel the distortion. These parameter changes enable distortion cancellation within a single amplifier chain.
Solution Approach 2:
The linear stage acts as an intermediary between the two non-linear stages. It receives the distorted signal from the first non-linear stage, inverts it, and passes it to the second non-linear stage. This intermediary function is crucial for establishing the correct phase relationship that enables distortion cancellation in the final stage.
Data Source
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.