RF Amplifier Feedback Circuit With Variable Injection Gain Control
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Solution Overview
Problem
Existing RF receiver front-end amplifier circuits face challenges in minimizing noise, maintaining input impedance, and reducing current consumption, especially at low gain settings, while also dealing with limited scalability and linearity issues.
Innovation Solution
The amplifier circuit employs a shunt-shunt feedback topology with transconductance circuitry that adjusts the point of current injection along a feedback resistance, allowing for variable gain control without changing the input impedance, and uses a complementary stage arrangement to reduce current consumption and improve noise figure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If current reduction techniques are implemented to reduce power consumption at low gain settings, then power consumption is reduced, but the transconductance of the amplifier changes causing input impedance mismatch
Solution Approach 1:
The patent introduces a feedback resistance as an intermediary element that mediates between the transconductance circuitry and the output. By adjusting the injection point along the feedback resistance, the system can independently control gain and maintain constant input impedance, resolving the contradiction between power reduction and impedance matching
Solution Approach 2:
The patent employs dynamic adjustment of the transconductance injection point along the feedback resistance based on the desired gain setting. This dynamic reconfiguration allows the amplifier to adapt its characteristics: at low gain settings, current consumption is reduced while the feedback mechanism maintains the required input impedance, thus resolving the contradiction
2Object-affected harmful factors
If inductively degenerated amplifier topology is used to reduce noise and increase transconductance, then noise performance is improved, but the input stage operates over narrow bandwidths requiring tuning for different frequency bands
Solution Approach 1:
The patent replaces the mechanical/resonant circuit approach (inductively degenerated amplifier with series RLC resonance) with an electronic feedback-based approach. The feedback resistance and transconductance circuitry provide gain control without requiring narrowband resonant circuits, thus achieving low noise performance with broadband operation and eliminating the need for tuning
Solution Approach 2:
The feedback-based amplifier topology serves multiple functions simultaneously: it provides noise reduction through the feedback mechanism, enables broadband operation without tuning, and allows for variable gain control. This universal approach resolves the contradiction between noise performance and bandwidth adaptability
3Object-affected harmful factors
If voltage amplification is provided before the first noisy component to reduce overall noise, then noise performance is improved, but the gate-source voltage swing of the transistor increases causing higher distortion
Solution Approach 1:
The patent employs feedback through the feedback resistance to control the amplifier operation. The feedback mechanism allows voltage amplification before the noisy component while simultaneously controlling the gate-source voltage swing to remain within linear regions, thus achieving noise reduction without excessive distortion through closed-loop control
Data Source
AI summary
An amplifier circuit for amplifying an input signal received at an input node of the amplifier circuit. The amplifier circuit comprises a feedback resistance connected between the input node of the amplifier circuit and an output node of the amplifier circuit. Transconductance circuitry is arranged to inject a transconductance current at a point along the feedback resistance. The transconductance circuitry is configurable to vary the point along the feedback resistance where the transconductance current is injected.