Adaptive Bias RF Power Amplifier With Feedback for Envelope Tracking
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Solution Overview
Problem
Power amplifiers in RF communication systems face challenges in efficiently managing power to prolong battery life and maintain suitable transmit power levels, particularly due to variations in RF signal envelopes, which can lead to inefficiencies and distortion.
Innovation Solution
The implementation of an adaptive bias power amplifier system that includes a current mirror and a field-effect transistor with a gate biased by an internal voltage, along with a choke inductor and a buffer, to dynamically adjust the power amplifier supply voltage based on the RF signal envelope, using an envelope tracker that combines a DC-to-DC converter and an error amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the power amplifier supply voltage is dynamically adjusted based on RF signal envelope, then power efficiency is improved, but gain variation and distortion increase due to transistor non-idealities
Solution Approach 1:
The patent implements a feedback mechanism where the drain voltage of the first NFET is fed back to adjust the gate voltage of the amplifying NFET. This feedback loop compensates for gain variation and distortion by dynamically adjusting the gate voltage in response to changes in drain voltage, thereby maintaining signal fidelity while enabling dynamic supply voltage adjustment for power efficiency.
Solution Approach 2:
The patent changes the operating parameters of the power amplifier by dynamically adjusting the supply voltage (VDD) based on the RF signal envelope. The envelope tracker modifies the DC-to-DC converter output to track the signal envelope, changing the supply voltage parameter in real-time to improve power efficiency while the adaptive bias circuit compensates for resulting distortions.
2Duration of action of moving object
If envelope tracking is implemented to improve power efficiency, then battery life is extended, but system complexity increases
Solution Approach 1:
The patent merges the adaptive bias circuit functionality into the existing power amplifier structure. The current mirror, buffer, and biasing components are integrated with the main amplifying NFET and supply voltage tracking circuitry, combining multiple functions (biasing, voltage tracking, and signal amplification) into a unified circuit architecture to manage system complexity.
Solution Approach 2:
The DC-to-DC converter is designed to serve multiple functions: it provides the supply voltage to the power amplifier and simultaneously tracks the RF signal envelope to generate the dynamic supply voltage profile. This multi-functionality reduces the need for separate dedicated circuits, thereby managing system complexity while achieving power efficiency improvements.
3Loss of energy
If dynamic supply voltage adjustment is used, then power efficiency improves, but bandwidth and signal fidelity deteriorate
Solution Approach 1:
The feedback mechanism compensates for bandwidth and signal fidelity deterioration by continuously monitoring the drain voltage and adjusting the gate voltage accordingly. This real-time correction maintains signal integrity and frequency response characteristics even as the supply voltage dynamically changes, preventing degradation of bandwidth and signal fidelity.
Solution Approach 2:
The adaptive bias circuit performs preliminary action by pre-establishing the appropriate gate voltage level based on the expected supply voltage changes. The current mirror and buffer circuitry are configured to anticipate and prepare the bias conditions before the full effect of supply voltage changes occurs, thereby maintaining signal fidelity and bandwidth performance.
Data Source
AI summary
Power amplifiers with adaptive bias for envelope tracking applications are provided herein. In certain embodiments, an envelope tracking system includes a power amplifier that amplifies a radio frequency (RF) signal and that receives power from a power amplifier supply voltage, and an envelope tracker that controls a voltage level of the power amplifier supply voltage based on an envelope of the RF signal. The power amplifier includes a current mirror having an input that receives a reference current, an output electrically connected to the power amplifier supply voltage, and a node that outputs a gate bias voltage. The power amplifier further includes a field-effect transistor that amplifies the radio frequency signal and a first depletion-mode transistor having a gate connected to the node of the current mirror and a source connected to a gate of the field-effect transistor.