Amplifier Self-Cancellation of Intermodulation Distortion
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Solution Overview
Problem
Nonlinear electronic devices, such as amplifiers, generate nth-order intermodulation products at high output power, leading to signal distortion and interference with other signals, which existing methods like predistortion, postdistortion, and feedforward techniques fail to effectively cancel due to complexity and limited reduction of intermodulation products.
Innovation Solution
A method involving the application of a test signal to measure nth- and mth-order intermodulation products, calculating transfer function coefficients, and using a baseband resistor to add the mth-order intermodulation product back into the input of the nonlinear device to cancel nth-order intermodulation products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high output power is used to meet performance requirements, then power and signal strength are improved, but nth-order intermodulation products increase exponentially causing signal distortion and interference
Solution Approach 1:
The patent applies second-order intermodulation products (which are typically harmful distortions) as a beneficial feedback signal to cancel third-order intermodulation products. By feeding back the second-order products through a carefully designed resistor network, the system converts these harmful distortions into a useful cancellation mechanism, achieving linearization without complex predistortion circuitry
Solution Approach 2:
The patent implements a feedback mechanism where second-order intermodulation products are extracted from the amplifier output, scaled by a baseband resistance, and fed back to the amplifier input. This feedback loop creates destructive interference that cancels the harmful third-order intermodulation products, enabling high-power operation with reduced distortion
2Manufacturing precision
If signal filtering techniques are used to remove intermodulation products, then signal purity is improved, but certain intermodulation products at or near input signal frequency cannot be effectively removed
Solution Approach 1:
The patent applies preliminary action by canceling third-order intermodulation products before they can contaminate the output signal band. By using second-order products to preemptively cancel the third-order distortions at the input stage, the system prevents these harmful frequencies from being generated in the first place, making subsequent filtering unnecessary for these components
3Object-generated harmful factors
If predistortion or postdistortion techniques are used to improve amplifier linearization, then intermodulation product reduction is achieved, but device complexity and power consumption increase
Solution Approach 1:
The patent implements self-service by using the amplifier's own second-order intermodulation products to cancel its third-order intermodulation products. The system requires no external predistortion circuitry or complex feedback networks - the amplifier literally uses its own distortions to clean itself up, achieving linearization with minimal additional components
Solution Approach 2:
The patent merges the function of distortion cancellation with the existing amplifier structure by utilizing the naturally generated second-order intermodulation products. Instead of adding separate predistortion or postdistortion circuits, the system combines the cancellation function with the amplifier's inherent nonlinearities, reducing overall device complexity
Data Source
AI summary
A method for reducing distortion in a nonlinear device whereby nth-order intermodulation products are canceled. A test signal is applied to the input of the nonlinear device and amplitudes of nth- and mth-order intermodulation products are measured. Transfer function coefficients and an optimum value of a baseband resistance are calculated. A baseband resistance is applied to an output of the device. An input signal is applied to the input of the device and a mth-order intermodulation product is passed through the baseband resistance and added back to the input. A system for practicing the same includes a signal source that generates the test signal, a unit that measures the intermodulation products, a unit that calculates the transfer function coefficients and the optimum value of a baseband resistance, and a unit that applies the baseband resistance to the output of the device.