Low-Noise Amplifier Feedback Circuit for Noise-Bandwidth Tradeoffs
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Solution Overview
Problem
Conventional low noise amplifiers (LNAs) face challenges in improving frequency characteristics while reducing noise, particularly due to increased parasitic capacitance and trade-offs between noise and frequency characteristics.
Innovation Solution
The proposed solution involves a low noise amplifier configuration that includes a common-gate amplifier circuit, an inverting amplifier circuit, and a negative feedback resistor inserted between the input and output terminals of the inverting amplifier circuit. This configuration reduces parasitic capacitance and improves impedance matching, thereby enhancing frequency characteristics and noise performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a common-source amplifier circuit is connected to the output of a common-gate amplifier circuit to achieve high gain and low noise, then noise characteristics improve, but parasitic capacitance increases and frequency characteristics deteriorate
Solution Approach 1:
The patent extracts the noise amplification function from the traditional common-source amplifier configuration and implements it through a negative feedback network connected to the common-gate amplifier. This separation allows the common-gate stage to handle high-frequency signals with low parasitic capacitance while the feedback network provides noise reduction, resolving the contradiction between noise performance and frequency characteristics.
Solution Approach 2:
The patent applies negative feedback by connecting a feedback network from the output to the input of the amplifier circuit. This feedback mechanism reduces the overall noise figure while maintaining stable gain across a wide frequency range, effectively decoupling the noise performance from the parasitic capacitance limitations of additional amplifier stages.
2Object-affected harmful factors
If load resistance is increased to reduce noise in the LNA, then noise characteristics improve, but gain variation due to frequency change increases and frequency characteristics deteriorate
Solution Approach 1:
The negative feedback network compensates for gain variations caused by frequency changes and load resistance variations. By feeding back a portion of the output signal to the input, the system maintains stable gain across the operating bandwidth while allowing the use of higher load resistance values for noise reduction.
Solution Approach 2:
The patent optimizes the impedance parameters of the common-gate amplifier and feedback network to achieve a balance between noise figure and gain stability. By carefully selecting the source impedance and feedback network parameters, the system achieves low noise performance with minimal gain variation across frequency.
Data Source
AI summary
In a low noise amplifier in which a common-source amplifier circuit is used, frequency characteristics are improved while noise is reduced.The low noise amplifier includes a common-gate amplifier circuit, an inverting amplifier circuit, and a negative feedback resistor. In the low noise amplifier, the common-gate amplifier circuit amplifies a reception signal and outputs the amplified reception signal as an internal signal. In addition, in the low noise amplifier, the inverting amplifier circuit inverts and amplifies the internal signal and outputs the inverted and amplified internal signal as an output signal. Moreover, the negative feedback resistor is inserted between an input terminal and an output terminal of the inverting amplifier circuit.