RF Amplifier Circuit With LC Resonance for Noise-Stable Output
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Solution Overview
Problem
Radio-frequency power amplifiers face challenges in achieving high saturated output and power-added efficiency while effectively suppressing out-of-band noise, due to phase shift issues and oscillation problems in existing designs.
Innovation Solution
A radio-frequency signal amplifier circuit with an LC series resonance circuit connected between a resistance element and the amplifier transistor, which complements the phase shift between voltage and current, and includes a second resistance element to prevent oscillation, thereby stabilizing amplification and suppressing out-of-band noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a series resonance circuit is connected between the amplifier transistor and bias circuit to suppress out-of-band noise, then out-of-band noise is suppressed, but oscillation easily occurs and the amplification operation becomes unstable
Solution Approach 1:
A first resistance element is introduced as an intermediary component between the amplifier transistor and the series resonance circuit. This resistance element acts as a mediator that prevents direct coupling between the RF signal path and the bias circuit, thereby suppressing oscillation while allowing the series resonance circuit to maintain its noise suppression function. The resistance element isolates the bias circuit from RF signals that would otherwise cause oscillation.
2Object-affected harmful factors
If the series resonance circuit is positioned to suppress noise, then out-of-band noise is reduced, but the phase shift between voltage and current cannot be sufficiently adjusted, reducing saturated output and power-added efficiency
Solution Approach 1:
The noise suppression function is segmented into two independent parts: (1) the first resistance element that prevents RF signal entry into the bias circuit and provides phase adjustment, and (2) the series resonance circuit that specifically targets difference frequency band noise. This segmentation allows each component to perform its function independently without interfering with the other, enabling both noise suppression and phase optimization.
3Reliability
If the first resistance element is connected between the signal input terminal and bias circuit to prevent oscillation, then oscillation is suppressed, but the radio-frequency transmission signal is attenuated
Solution Approach 1:
The first resistance element is strategically positioned at a specific location where it provides maximum oscillation suppression with minimum impact on the RF transmission signal. By connecting it between the signal input terminal and the bias circuit rather than in the main RF path, the resistance element locally suppresses oscillation at the bias circuit interface while allowing the RF signal to pass through with minimal attenuation.
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
This configuration improves saturated output and power-added efficiency while stably suppressing out-of-band noise, enhancing amplification performance and noise suppression in multi-band communication devices.
Implementation Method 1
an induction-capacitance (LC) series resonance circuit that has one end connected to a node between the first resistance element and the signal input terminal and the other end connected to a grounding terminal and includes an inductor and a capacitor that are connected in series to each other. A resonant frequency of the LC series resonance circuit is included in a difference frequency band between the radio-frequency transmission signal and the radio-frequency reception signal.
Data Source
AI summary
A radio-frequency signal amplifier circuit that is used in a front-end circuit and that propagates a radio-frequency transmission signal and a radio-frequency reception signal is described. The amplifier circuit has an amplifier transistor, a bias circuit, a resistor, and an LC series resonance circuit. The LC series resonant circuit has one end that is connected to a node between the resistor and a signal input terminal, and has another end that is connected to a grounding terminal. A resonant frequency of the LC series resonance circuit is included in a difference frequency band between the frequencies of the transmission signal and the reception signal.