LNA Input Impedance Circuit With Negative Coupling Matching
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Solution Overview
Problem
Existing low-noise amplifiers (LNAs) suffer from poor impedance matching between the input impedance and the output impedance of the filter, which degrades the performance of the filter and increases noise figure, and existing solutions using off-chip elements degrade the performance of the filter and increase the form factor and cost.
Innovation Solution
An input impedance adjustment circuit is used to adjust the input impedance of the LNA by coupling an inductor and capacitor in series with negative magnetic coupling to cancel the effect of negative capacitance, thereby improving impedance matching and reducing noise figure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If off-chip elements are used to adjust input impedance, then impedance matching is improved, but form factor and cost increase
Solution Approach 1:
The patent combines the input impedance adjustment function with the existing LNA circuit by integrating an inductor and capacitor directly into the chip. The inductor is coupled between the gate of the first transistor and ground, while the capacitor is coupled between the drain of the first transistor and ground, merging the impedance matching function into the core LNA structure rather than using separate off-chip components.
Solution Approach 2:
The patent introduces an intermediary circuit consisting of a specifically designed inductor and capacitor combination that acts as a mediator between the filter output and the LNA input. This intermediary network transforms the impedance relationship without requiring external components, resolving the contradiction between achieving good impedance matching and maintaining compact form factor.
2Manufacturing precision
If off-chip elements are used to adjust input impedance, then impedance matching is improved, but cost increases
Solution Approach 1:
The patent merges the impedance adjustment function into the on-chip LNA structure, eliminating the need for separate off-chip inductors and capacitors. This integration reduces component count and assembly complexity, thereby reducing manufacturing cost while maintaining impedance matching performance.
Solution Approach 2:
The LNA circuit is designed to be self-adjusting for impedance matching through the integrated inductor and capacitor. The circuit automatically achieves optimal impedance matching without requiring external adjustment components or complex manufacturing processes, making production simpler and more cost-effective.
3Device complexity
If negative capacitance effect is not cancelled, then circuit is simpler, but noise figure increases
Solution Approach 1:
The patent converts the harmful negative capacitance effect into a beneficial impedance matching mechanism. By intentionally introducing a capacitor that exploits the negative capacitance phenomenon of the first transistor, the circuit achieves improved input impedance matching. The inductor and capacitor are specifically designed to cancel the negative capacitance effect, transforming what would be a harmful distortion into a useful impedance transformation mechanism, thereby reducing noise figure without excessive circuit complexity.
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
The input impedance adjustment circuit enhances impedance matching between the LNA and the filter, improving the performance of the filter and reducing noise figure without increasing the form factor or cost.
Implementation Method 1
a second inductor, wherein the second inductor is coupled with the first inductor through negative magnetic coupling
Data Source
AI summary
Aspects of the present disclosure provide a circuit configured to adjust an input impedance of an amplifier such as a low-noise amplifier. In certain aspects, the circuit is coupled to a node, wherein the node is between a first transistor and a second transistor of the amplifier. The circuit may include an inductor and a capacitor coupled in series, wherein the inductor is coupled with one or more load inductors of the amplifier through negative magnetic coupling.