Gain-Shaped Envelope Tracking Power Amplifiers for Linearity
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Solution Overview
Problem
Power amplifiers in RF communication systems face inefficiencies and linearity degradation due to limited gain shaping capabilities, particularly when operating with envelope tracking, leading to suboptimal peak power added efficiency (PAE) and increased heat dissipation.
Innovation Solution
The implementation of a gain shaping circuit that adjusts the bias of the power amplifier based on a gain shaping current, which is generated in response to the voltage level of the supply voltage from an envelope tracker, allowing for flexible gain expansion and compression across different voltage levels, thereby enhancing PAE while maintaining linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If envelope tracking is used to control supply voltage, then power efficiency is improved, but gain linearity deteriorates
Solution Approach 1:
A gain shaping circuit is introduced as an intermediary component between the envelope tracker and the power amplifier. This circuit receives the envelope signal and generates a gain shaping current that compensates for the non-linear gain variations caused by envelope tracking, thereby maintaining linearity while preserving the power efficiency benefits of voltage control.
Solution Approach 2:
The gain shaping circuit dynamically adjusts the bias current of the power amplifier based on the supply voltage level. By changing the bias current parameter in response to voltage changes, the circuit compensates for gain compression or expansion effects, maintaining linear operation across varying power efficiency conditions.
2Power
If gain expansion is increased to improve PAE, then peak power added efficiency is improved, but linearity performance deteriorates
Solution Approach 1:
The gain shaping circuit implements a feedback mechanism where the envelope signal is monitored and used to adjust the bias current. This feedback loop detects gain deviations caused by excessive expansion and compensates by adjusting the bias, thereby maintaining linearity while allowing the system to operate at optimal PAE points.
Solution Approach 2:
The bias current is made dynamic rather than fixed, allowing real-time adjustment based on the operating point. The gain shaping circuit continuously adapts the bias current to maintain optimal linearity across the full range of power output levels, enabling the system to achieve high PAE without sacrificing linearity performance.
3Device complexity
If fixed bias is used to simplify circuit design, then device complexity is reduced, but adaptability to voltage variations deteriorates
Solution Approach 1:
The bias control function is segmented into two independent parts: a fixed bias component and a dynamic gain shaping component. The fixed bias provides the baseline operating point with simple circuitry, while the gain shaping circuit adds only the necessary dynamic adjustment capability, minimizing overall complexity while achieving full adaptability.
Solution Approach 2:
The gain shaping circuit is designed to work with various power amplifier configurations and envelope tracking implementations. By creating a universal bias control mechanism that can adapt to different voltage variations, the circuit maintains simplicity while providing broad adaptability across different operating conditions and device types.
Data Source
AI summary
Envelope tracking power amplifiers with advanced gain shaping are provided. In certain implementations, a power amplifier system includes a power amplifier that amplifies a radio frequency (RF) signal and an envelope tracker that controls a voltage level of a supply voltage of the power amplifier based on an envelope of the RF signal. The power amplifier system further includes a gain shaping circuit that generates a gain shaping current that changes with the voltage level of the supply voltage from the envelope tracker. For example, the gain shaping circuit can include an analog look-up table (LUT) mapping a particular voltage level of the supply voltage to a particular current level of gain shaping current. Additionally, the gain shaping circuit biases the power amplifier based on the gain shaping current.