Low-Gain LNA Feedback Circuit for Third-Order Distortion Cancellation
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Solution Overview
Problem
Low-gain low noise amplifiers (LNAs) produce undesired third-order intermodulation components due to transistor non-linear characteristics, distorting the output RF signal.
Innovation Solution
Incorporating an impedance matching circuit, an output impedance circuit, and a first tank circuit to generate resonance impedance at twice the input frequency, combining input and feedback RF signals to cancel third-order intermodulation components with equal and opposite magnitude and phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-gain LNA is used to maintain low noise figure, then noise performance is improved, but third-order intermodulation distortion increases due to transistor non-linear characteristics
Solution Approach 1:
The patent applies feedback by extracting a portion of the output signal and feeding it back to the input through a feedback network. This feedback mechanism is specifically designed to generate third-order distortion components that are equal in magnitude but opposite in phase to the unwanted intermodulation products, thereby canceling them out and improving linearity while maintaining low gain operation
Solution Approach 2:
The patent implements preliminary anti-action by pre-generating cancellation signals through the feedback path before they combine with the main signal at the input. The feedback network is configured to produce third-order distortion components in advance that will destructively interfere with the harmful intermodulation products, preventing their harmful effect on the output signal
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
Substantially reduces third-order intermodulation distortion in the output RF signal, improving signal linearity and reducing distortion.
Implementation Method 1
a first tank circuit configured to produce a resonance impedance at a first frequency substantially twice a second frequency of the input RF signal
Data Source
AI summary
An aspect of the disclosure relates to a method of reducing a third-order intermodulation component at a first terminal of a transistor, including: receiving an input radio frequency (RF) signal cycling with a first frequency at a control terminal of the transistor; generating a feedback RF signal cycling at a second frequency at a second terminal of the transistor, wherein the second frequency is substantially twice the first frequency; and generating a third-order intermodulation cancellation component at the first terminal including combining the input RF signal with the feedback RF signal, wherein the third-order intermodulation cancellation component has a magnitude and phase substantially equal to and opposite a magnitude and phase of the third-order intermodulation component at the first terminal of the transistor, respectively.