RF Power Amplifier Limiter Circuit for Input-Amplitude Power Control
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Solution Overview
Problem
Existing limiter circuits for power amplifier circuits in wireless communication terminals fail to effectively limit output power based on input signal amplitude, leading to potential over-input issues in subsequent amplifier stages due to counteracting effects between supply voltage and bias current limitations.
Innovation Solution
A limiter circuit that includes an input signal detection transistor and a voltage limiting transistor, connected in a configuration where the voltage applied to the amplifying transistor is controlled based on the current flowing to the input signal detection transistor, effectively limiting output power by adjusting the supply voltage in response to input signal amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a bias voltage is applied to the drain of a FET via a resistor to limit bias current with the increase of an input signal, then bias current limitation effect is provided, but an increase in supply voltage countervails the bias current limitation effect and thus a sufficient output power reduction effect is not provided
Solution Approach 1:
The patent employs feedback mechanisms where the limited output signal from the amplifier circuit is fed back to control the supply voltage of subsequent amplifier stages. This feedback loop ensures that when output power increases beyond a certain level, the supply voltage is automatically reduced, thereby maintaining effective power limitation despite variations in bias current. The feedback principle directly addresses the contradiction by creating a self-regulating system that prioritizes output power control.
Solution Approach 2:
The patent dynamically changes the supply voltage parameter of amplifier circuits based on the amplitude level of input signals. By adjusting the supply voltage in response to signal conditions, the system achieves effective output power limitation. This parameter change approach allows the power amplifier to adapt its operating characteristics, ensuring that output power remains within desired limits while accounting for the counteracting effect of supply voltage increases on bias current limitation.
2Use of energy by moving object
If amplifier circuits with a plurality of stages are connected in a multi-stage connection configuration to improve power efficiency, then power efficiency is improved, but excessive increase in output power of a previous stage leads to over input to a subsequent stage
Solution Approach 1:
The patent implements preliminary action by limiting the output power of each amplifier stage before the signal is passed to the next stage. The limiter circuits are positioned at the output of each amplifier stage to proactively prevent excessive power levels from developing. This preliminary limitation ensures that even if one stage produces excessive power, subsequent stages are protected from over-input conditions, thereby maintaining the integrity of the multi-stage configuration while preserving power efficiency benefits.
Solution Approach 2:
The patent introduces limiter circuits as intermediary elements between amplifier stages in the multi-stage configuration. These limiter circuits act as mediators that control and regulate the signal power level passing between stages. By placing these intermediary limiting devices, the system maintains the power efficiency advantages of multi-stage amplification while preventing the harmful over-input effect from propagating through the signal chain.
3Power
If a limiter circuit is designed to limit output power based on input signal amplitude, then output power limitation is achieved, but the circuit complexity increases
Solution Approach 1:
The patent merges the limiter circuit functionality with the existing amplifier circuit structure. Rather than adding completely separate limiting components, the design integrates power limitation functions into the amplifier stages themselves, using shared components and control paths. This merging approach achieves effective output power limitation based on input signal amplitude while minimizing the increase in overall circuit complexity by leveraging existing circuit elements for multiple purposes.
Data Source
AI summary
There is provided a limiter circuit and a power amplifier circuit that are capable of effectively limiting output power of an amplifying transistor based on the amplitude of an input signal. A limiter circuit is connectable to an amplifying transistor that amplifies and outputs a radio frequency signal and controls a voltage to be applied to the amplifying transistor, based on the radio frequency signal. The limiter circuit includes an input signal detection transistor that detects power of the radio frequency signal and a voltage limiting transistor that limits the voltage to be applied to the amplifying transistor, based on current flowing to the input signal detection transistor.