RF Power Amplifier Biasing for Temperature-Stable Linearity
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Solution Overview
Problem
RF power amplifiers in wireless communication devices face challenges in maintaining high linearity and efficiency due to temperature-dependent current gain variations in bipolar junction transistors, leading to potential signal distortion, especially with high peak-to-average power ratio modulation techniques like OFDM.
Innovation Solution
The RF power amplifier design incorporates an adder circuit, output-stage circuit, and differential circuit to generate an adder voltage with temperature compensation, using a bandgap reference circuit to stabilize the reference voltage and feedback voltage, ensuring the output current remains temperature-independent, thus maintaining high linearity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a bandgap reference circuit is used as a bias circuit to provide a reference voltage with close to zero temperature coefficient, then the reference voltage stability is improved, but the current gain of bipolar junction transistor decreases with increasing temperature leading to reduced output current and output power
Solution Approach 1:
The patent changes the temperature coefficient parameter of the reference voltage from zero (bandgap) to positive temperature coefficient. By making the reference voltage have a positive temperature coefficient, it compensates for the negative temperature coefficient of the bipolar junction transistor's current gain, thereby maintaining stable output current and output power across temperature variations.
2Power
If the current gain of bipolar junction transistor is used for amplification, then the amplification capability is improved, but the linearity deteriorates due to negative temperature coefficient causing current gain to decrease with increasing temperature
Solution Approach 1:
The patent introduces a feedback mechanism where the output current is fed back through a feedback resistor to generate a feedback voltage. This feedback voltage is added to the reference voltage in the adder circuit, creating a closed-loop control system that automatically adjusts the base current to compensate for temperature-induced current gain variations, thereby maintaining linearity.
Solution Approach 2:
The patent changes the temperature characteristic parameter of the reference voltage from zero temperature coefficient to positive temperature coefficient. This parameter change enables the reference voltage to track and compensate for the negative temperature coefficient of the transistor's current gain, maintaining constant output current and improving linearity across temperature ranges.
3Productivity
If high peak-to-average power ratio modulation like OFDM is used to improve communication efficiency, then the data transmission capability is improved, but the demand for linearity of RF power amplifier increases leading to signal distortion
Solution Approach 1:
The patent employs a feedback mechanism where the output current is sensed and fed back to the adder circuit. This feedback loop continuously monitors and compensates for non-linear distortions caused by high PAPR modulation, maintaining signal linearity even under dramatic wave packet variations characteristic of OFDM systems.
Solution Approach 2:
The patent modifies the temperature coefficient parameter of the reference voltage to be positive, which compensates for temperature-induced non-linearities in the power amplifier. This parameter change ensures that the amplifier maintains high linearity across temperature variations, preventing signal distortion during high data rate OFDM transmission.
Data Source
AI summary
A radio frequency (RF) power amplifier is disclosed. The RF power amplifier includes an adder circuit, an output-stage circuit and a differential circuit. The adder circuit has a first ratio and a second ratio, and receives a reference voltage and a feedback voltage so as to output an adder voltage after an operation, wherein the feedback voltage is a voltage with a negative temperature coefficient, and the reference voltage is sum of a first voltage with a negative temperature coefficient and a second voltage with positive temperature coefficient. The output-stage circuit is used for providing the feedback voltage. The differential circuit has a first multiplier factor, and the differential circuit makes the first multiplier factor be multiplied with the adder voltage so as to provide a voltage to the output-stage circuit. The RF power amplifier stabilizes an output current through adjusting the temperature coefficient of the reference voltage.