LNA Neutralization Circuit for Wideband Noise Cancellation
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Solution Overview
Problem
Existing low-noise amplifiers face challenges in achieving compact form factors while maintaining desirable noise figures over both lower and higher gain ranges, and previous noise cancellation techniques result in severe limitations in broadband capabilities due to parasitic capacitance at the impedance amplifier output.
Innovation Solution
A low-noise amplifier system with a dual-path architecture that includes an impedance amplifier for input impedance matching and noise cancellation, utilizing a neutralization amplifier to reduce parasitic capacitive loading, and a main amplifier for wideband amplification with adjustable gains, all integrated in a standard semiconductor process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If noise cancellation techniques are applied to achieve compact form factors by eliminating large input match inductors, then device size is reduced, but broadband capabilities are severely limited due to parasitic capacitance at the impedance amplifier output
Solution Approach 1:
A neutralization amplifier is introduced as an intermediary component between the impedance amplifier and main amplifier. This neutralization amplifier specifically targets and compensates for the parasitic capacitance at the impedance amplifier output, allowing the noise cancellation architecture to maintain broadband performance while achieving compact form factor without large input match inductors
2Reliability
If noise cancellation is applied to fixed gain LNAs or maximum gain state of variable gain amplifiers, then noise figure is improved at maximum gain, but noise figure degrades at lower gains
Solution Approach 1:
The system employs a variable gain main amplifier that can dynamically adjust its gain level. The noise cancellation architecture is designed to work effectively across the full gain range by maintaining proper impedance matching and noise cancellation at each gain setting, allowing the LNA to achieve low noise figure at both maximum and lower gain states rather than only at fixed or maximum gain
3Reliability
If dual-path architecture with impedance amplifier and main amplifier is used to achieve noise cancellation, then noise figure is reduced, but parasitic capacitive loading increases
Solution Approach 1:
The neutralization amplifier serves as a mediator that specifically addresses the parasitic capacitive loading introduced by the dual-path architecture. It compensates for this parasitic capacitance at the impedance amplifier output, allowing the beneficial noise cancellation effect to be maintained while eliminating the harmful parasitic loading that would otherwise limit broadband performance
Data Source
AI summary
Disclosed is a low noise amplifier system. Included is a main amplifier having a main input coupled to a RF input and a main output connected to an RF output and an impedance amplifier having an impedance input coupled to the RF input and an impedance output coupled to the RF output, wherein the impedance amplifier is configured to provide input impedance matching to the main amplifier. The impedance amplifier also provides a first noise path that passes through the impedance amplifier such that the noise generated by the impedance amplifier is substantially out of phase with the noise that passes through a second noise path that passes through the main amplifier. A neutralization amplifier is configured to reduce parasitic capacitive loading within the first noise path.