RF Amplifier Bias and Impedance Switching for Low-Power Linearity
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Solution Overview
Problem
In wireless communications systems, power amplifiers face a challenge in maintaining linearity when operating in low power mode, as reducing bias current leads to a sharp rise in error vector magnitude (EVM) and reduced output signal quality.
Innovation Solution
The amplification circuit incorporates an impedance unit that adjusts capacitive impedance based on selection signals to maintain linearity across different power modes, using a combination of switches, capacitors, and transistors to control bias current and improve signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the bias current is reduced to operate the power amplifier in low power mode, then the power consumption is reduced, but the linearity of the power amplifier deteriorates and the output signal quality decreases
Solution Approach 1:
The patent changes the impedance parameter (capacitance value) according to the power mode. In low power mode, a first capacitance value is used, while in high power mode, a second capacitance value is used. This parameter change allows the circuit to maintain optimal linearity for each power mode while achieving power savings in low power mode.
Solution Approach 2:
The patent dynamically switches between different capacitance values based on the power mode requirement. The switching mechanism allows the impedance to be adjusted in real-time, enabling the power amplifier to adapt its characteristics to maintain linearity whether operating in high or low power mode.
2Use of energy by moving object
If the bias current is reduced to operate the power amplifier in low power mode, then the power consumption is reduced, but the error vector magnitude (EVM) increases sharply
Solution Approach 1:
The patent changes the capacitive impedance parameter based on power mode to compensate for the EVM degradation that occurs when bias current is reduced. By adjusting the capacitance value in low power mode, the circuit maintains better signal quality and lower EVM despite the reduced bias current.
3Reliability
If different capacitance values are used for different power modes, then the linearity is maintained across modes, but the circuit complexity increases
Solution Approach 1:
The patent segments the impedance adjustment function into discrete capacitance values corresponding to different power modes. Instead of using a continuous variable impedance element, the circuit uses switched capacitors that provide specific capacitance values for high and low power modes, simplifying the overall circuit structure while maintaining effectiveness.
Data Source
AI summary
An amplification circuit includes an input terminal, an output terminal, a capacitor, a bias unit, an amplification unit, and an impedance unit. The input terminal receives a radio frequency signal. The capacitor is coupled to the input terminal and the bias unit. The bias unit includes a transistor for controlling the bias current. The transistor has a first terminal for receiving a system voltage, and a control terminal coupled to the reference voltage terminal. The amplification unit has an input terminal coupled to the capacitor and the bias unit, and an output terminal coupled to the output terminal of the amplification circuit. The impedance unit has a first terminal coupled to the bias unit, and a second terminal coupled to the input terminal of the amplification circuit and the capacitor. The impedance unit adjusts the amplifying linearity of the amplification circuit according to a selection signal.