LNA Amplification Circuit With Active Admittance for Low-Power Gain
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Solution Overview
Problem
Low Noise Amplifiers (LNAs) face challenges in achieving low noise figure and high gain while maintaining low power consumption, particularly in radio frequency circuits, due to the limitations of passive inductors and existing amplification techniques, which often result in high surface area occupation and increased cost.
Innovation Solution
The proposed amplification circuit distributes input admittance between multiple admittances, allowing for a better input admittance to electrical consumption ratio by using a combination of main and secondary amplifiers with variable gains, along with neutralization connections and tertiary amplification, to achieve lower input impedance and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive inductors are used to adapt LNA to low impedance, minimize self-noise and maximize gain, then the noise figure and gain performance are improved, but the surface area occupation increases significantly
Solution Approach 1:
The patent extracts and eliminates the passive inductor components from the LNA circuit. Instead of using traditional inductors for impedance matching and gain enhancement, the invention employs an active circuit implementation using transistors and capacitors that achieves the same functional effects without requiring large inductor surface areas, thereby resolving the contradiction between noise figure performance and surface area occupation
Solution Approach 2:
The patent substitutes the passive mechanical inductor components with an active electronic system based on transistor amplification stages. The active circuit uses controlled current sources and transconductance mechanisms to achieve impedance transformation and gain without relying on physical inductors, thus reducing surface area while maintaining or improving noise figure performance
2Reliability
If the noise figure of LNA is reduced below 1 dB, then the noise performance is significantly improved, but the power consumption becomes very high (more than ten milliwatts)
Solution Approach 1:
The patent employs dynamic biasing and control mechanisms where the transistor operating points and circuit parameters can be optimized to achieve low noise figure only when necessary, rather than continuously operating at high power consumption. The active circuit allows dynamic adjustment of gain and impedance matching conditions to minimize power while maintaining acceptable noise performance
Solution Approach 2:
The invention changes the fundamental operating parameters of the LNA by using active transistor-based impedance transformation instead of passive inductive loading. This parameter change allows the circuit to achieve low noise figure through transconductance control rather than high bias currents, thereby reducing power consumption while maintaining noise performance
3Ease of operation
If the input impedance of LNA is matched to 50 Ω standard, then the impedance matching and signal transfer efficiency are improved, but the input admittance is limited which requires higher power consumption to increase
Solution Approach 1:
The patent implements feedback mechanisms in the active LNA circuit where the output is fed back to control the input impedance. This feedback allows the circuit to dynamically adjust and maintain 50 Ω impedance matching without requiring excessive power consumption, as the feedback control optimizes the operating conditions to achieve matching efficiently
Solution Approach 2:
The patent replaces the passive impedance matching network (which would require additional power to adjust and maintain) with an active transistor-based impedance transformation circuit. The active circuit uses controlled current sources and transconductance to achieve impedance matching, eliminating the need for power-hungry passive matching components and allowing better control over the input admittance
Data Source
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AI summary
The invention relates to an amplification circuit comprises an input (IN) intended to receive an input voltage (vIN), an output (OUT) intended to present an output voltage (vOUT), a main amplifier (202) designed to receive the input voltage (vIN) from the input (IN), to receive a main control voltage (vCTL,1), to amplify the input voltage (vIN) by a main gain (G1) dependent on the control voltage (vCTL,1), the output voltage (vOUT) corresponding to the input voltage (vIN) thus amplified, and to provide the output voltage (vOUT) to the output (OUT); and a second amplifier (212) designed to receive the input voltage (vIN) from the input (IN), to amplify the input voltage (vIN) by a secondary gain (G2), the main control voltage (vCTL,1) corresponding to the input voltage (vIN) thus amplified, and to provide the main control voltage (vCTL,1) to the main amplifier (A1). During operation, the secondary amplifier (212) has an input admittance (g2) of at least 1 millisiemens.