Hybrid RF Power Amplifier Supply Circuit for Envelope Tracking
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Solution Overview
Problem
Existing power amplification technologies face inefficiencies when generating supply voltage for RF power amplifiers, particularly at low battery voltages, and struggle with noise and bandwidth requirements, with linear amplifiers being inefficient at low output voltages and switching converters having limited bandwidth and noise issues.
Innovation Solution
A circuit and method combining a switching converter and a linear amplifier to generate supply voltage for RF power amplifiers, where the switching converter provides peak power and the linear amplifier performs envelope tracking, allowing for efficient power regulation and modulation control while managing noise and bandwidth effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a linear amplifier is used to generate supply voltage VCC for a power amplifier, then low noise and high bandwidth are achieved, but efficiency deteriorates when VCC is far below battery voltage VBATT
Solution Approach 1:
The power supply system is segmented into two stages: a switching converter stage for gross power conversion and a linear amplifier stage for fine regulation. The switching converter handles the large voltage difference between VBATT and VCC to maintain efficiency, while the linear amplifier handles small adjustments to maintain low noise and high bandwidth performance.
Solution Approach 2:
The system dynamically switches between switching converter operation and linear amplifier operation based on the voltage difference between VBATT and VCC. When the voltage difference is large, the switching converter is active; when the voltage difference is small, the linear amplifier takes over, optimizing performance across varying operating conditions.
2Loss of energy
If a switching converter is used to generate supply voltage VCC, then efficiency is improved, but bandwidth and noise performance deteriorate
Solution Approach 1:
The power supply function is divided between a switching converter for efficient power conversion and a linear amplifier for low-noise regulation. The switching converter operates at fixed voltage steps while the linear amplifier provides continuous voltage adjustment, separating the efficiency-critical function from the noise-critical function.
Solution Approach 2:
The linear amplifier acts as an intermediary between the switching converter and the power amplifier. It filters out switching noise and provides smooth voltage modulation, mediating between the high-efficiency but noisy switching converter and the noise-sensitive power amplifier.
3Speed
If switching frequency is increased to improve response time, then bandwidth is improved, but switching losses and noise increase
Solution Approach 1:
The frequency response function is segmented between the switching converter and linear amplifier. The switching converter operates at a fixed, relatively low frequency for efficient power conversion, while the linear amplifier provides high-frequency voltage modulation without switching losses, as it operates in continuous conduction mode.
Data Source
AI summary
A power amplifier receives an input signal and generates an amplified output signal. A switching converter generates a regulated voltage and performs power control for the power amplifier. A linear amplifier performs modulation envelope control for the power amplifier. The switching converter may be coupled in series with the linear amplifier, and this circuit may operate in one of multiple modes. For example, the linear amplifier may output a tracked voltage to the power amplifier in GSM/polar EDGE mode, and the switching converter may output the regulated voltage to the power amplifier in WCDMA/UMTS mode. The linear amplifier could also output the tracked voltage in both modes, and a selector could select the appropriate feedback voltage for the switcher. The switching converter could also provide the regulated voltage directly to the power amplifier, and the linear converter could adjust a bias of the power amplifier to provide envelope tracking.