Power Amplifier Bias Control for High-Output Linearity
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Solution Overview
Problem
Existing power amplifier modules experience a decrease in linearity of output power characteristics with respect to input power as the output power approaches rated output power, leading to degradation in adjacent channel leakage ratio (ACLR) and error vector magnitude (EVM).
Innovation Solution
A power amplifier circuit is designed to include an amplifier circuit with a first bipolar transistor, a bias circuit with an emitter follower, a detector to monitor the power supply voltage, and a control circuit with a current limiting circuit. The control circuit adjusts the upper limit value of the control current based on the detected power supply voltage, improving the linearity of output power characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the control current is increased to improve output power, then the output power increases, but the linearity of output power characteristics deteriorates
Solution Approach 1:
The patent implements dynamic control of the control current by introducing a current limiting circuit that adjusts the upper limit value of the control current based on detected power supply voltage. This dynamic adjustment mechanism allows the system to optimize the balance between output power and linearity by adapting the current limit to changing operating conditions, thereby resolving the contradiction between maximizing output power and maintaining linearity.
Solution Approach 2:
The patent employs a feedback mechanism where a detector monitors the power supply voltage and provides this information to the control circuit. The control circuit then adjusts the upper limit value of the control current accordingly. This closed-loop feedback system enables real-time optimization of the control current to maintain optimal linearity while achieving the required output power level.
2Power
If the control current is increased to approach rated output power, then the output power increases, but the adjacent channel leakage ratio and error vector magnitude are degraded
Solution Approach 1:
The current limiting circuit dynamically adjusts the upper limit value of the control current based on the detected power supply voltage, preventing the control current from exceeding optimal levels that would cause ACLR and EVM degradation. This dynamic control ensures that the amplifier operates within the linear region even at high output power levels, thereby maintaining signal quality and reliability.
Solution Approach 2:
The patent applies preliminary anti-action by proactively limiting the control current before it can cause harmful effects. The current limiting circuit prevents the control current from reaching levels that would lead to ACLR and EVM degradation, thus counteracting potential harm before it occurs and maintaining reliable operation.
Data Source
AI summary
A power amplifier circuit includes an amplifier circuit, a bias circuit, a detector, and a control circuit. The amplifier circuit includes a first bipolar transistor. The bias circuit includes an emitter follower. The emitter follower includes a second bipolar transistor and supplies a bias current to the base of the first bipolar transistor. The detector detects the voltage of a power supply terminal connected to the collector of the first bipolar transistor. The control circuit includes a current limiting circuit disposed between a battery terminal and the collector of the second bipolar transistor. The control circuit changes an upper limit value of a control current to be supplied to the collector of the second bipolar transistor, based on the voltage detected by the detector.