Automatic Bias Control Circuit for Linear PA Current and Linearity
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Solution Overview
Problem
Conventional linear power amplifiers in cellular handsets consume excessive current at low power output levels, exceeding minimum specified linearity requirements, leading to reduced battery life due to the tradeoff between current consumption and linearity.
Innovation Solution
An automatic bias control circuit that converts the RF output signal to a control signal linearly proportional to the RF output power, adjusting the quiescent current of the power amplifier to optimize current consumption while meeting minimum linearity requirements, using a peak detector/log converter circuit and DC reference circuit coupled with a differential amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the linear power amplifier is optimized to meet linearity requirements at the highest output power level, then linearity is improved, but current consumption increases excessively at low power output levels
Solution Approach 1:
The patent implements dynamic bias control that automatically adjusts the quiescent current of the power amplifier based on the actual output power level. The autobias control circuit continuously monitors the RF output signal and dynamically modifies the bias voltage to optimize the tradeoff between linearity and current consumption for each operating condition, rather than using a fixed bias point optimized for maximum power.
Solution Approach 2:
The patent employs a feedback mechanism where the autobias control circuit receives the RF output signal from the power amplifier, processes it through a peak detector and log converter, and uses the resulting control signal to adjust the bias voltage. This closed-loop feedback system ensures that the amplifier automatically adapts its bias point to maintain optimal linearity while minimizing current consumption at each operating level.
2Use of energy by moving object
If the quiescent current is reduced to minimize battery power consumption, then current consumption is improved, but linearity performance deteriorates below minimum specified requirements
Solution Approach 1:
The system dynamically adjusts the quiescent current based on the actual operating conditions rather than using a static low-current bias point. When high linearity is needed (at higher power levels), the bias is increased accordingly. When low power operation is sufficient, the bias is reduced to minimize current consumption, thus maintaining linearity above minimum requirements while optimizing power efficiency.
Solution Approach 2:
The patent changes the bias voltage parameter dynamically based on the output power level. The autobias control circuit generates a control signal that varies the bias voltage to achieve the optimal operating point for each power level, ensuring linearity requirements are met without excessive current consumption. This parameter adjustment allows the system to adapt to different operating conditions in real-time.
3Manufacturing precision
If conventional linear power amplifiers operate at fixed bias optimized for maximum power, then linearity at high power is improved, but battery life is reduced due to excessive current at low power levels
Solution Approach 1:
The patent transforms the fixed bias operation into dynamic bias control that adapts to the actual power output requirements. The autobias control circuit continuously adjusts the quiescent current based on the RF output signal, allowing the amplifier to consume minimal current during low-power operations (extending battery life) while maintaining optimal linearity performance when high power is actually needed.
Solution Approach 2:
The power amplifier system performs self-adjustment through the autobias control circuit, which automatically monitors the output signal and modifies the bias conditions without external intervention. This self-service mechanism ensures that the amplifier optimizes its own power consumption and linearity performance based on real-time operating conditions, thereby extending battery life while maintaining communication quality.
Data Source
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AI summary
According to an exemplary embodiment, an amplification module includes a power amplifier configured to receive an RF input signal and provide an RP output signal. The amplification module further includes an autobias control circuit configured to receive and convert the RF output signal to a control signal. The control signal can cause the power amplifier to have a quiescent current that increases substantially linearly in response to an increase in the RF output power of the RF output signal. The autobias control circuit can include a peak detector/log converter circuit coupled to a first input of a differential amplifier, where the differential amplifier outputs the control signal. The autobias control circuit can further include a DC reference circuit coupled to a second input of the differential amplifier. The amplification module further includes an analog bias circuit coupling the control voltage to a bias input of said power amplifier.