Adaptive Bias RF Power Amplifier for Stable 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 in mobile devices, due to variations in RF signal envelopes and non-idealities in field-effect transistors like short channel metal oxide semiconductor transistors.
Innovation Solution
The implementation of a power amplifier with adaptive bias using a current mirror and a choke inductor, where the internal voltage of the current mirror adjusts based on the power amplifier supply voltage, and a buffer is used to generate a gate bias voltage for the field-effect transistor, enabling efficient envelope tracking and compensating for transistor non-idealities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If envelope tracking is used to dynamically adjust power amplifier supply voltage to prolong battery life, then power efficiency improves, but gain variation and signal distortion increase due to non-idealities in field-effect transistors
Solution Approach 1:
The patent implements a feedback mechanism where the drain voltage of the first NFET in the Wilson current mirror is fed back to adjust the gate voltage of the power amplifier transistor. This feedback loop dynamically compensates for gain variation caused by envelope tracking, maintaining stable amplification while improving power efficiency.
Solution Approach 2:
The patent changes the operating parameters of the field-effect transistor by dynamically adjusting the gate voltage based on the drain voltage of the current mirror transistor. This parameter adjustment compensates for non-idealities in short channel transistors, reducing signal distortion while maintaining the power efficiency benefits of envelope tracking.
2Power
If Wilson current mirror is used to generate gate bias voltage for power amplifier, then power added efficiency improves, but circuit complexity increases
Solution Approach 1:
The Wilson current mirror circuit performs multiple functions: it generates the gate bias voltage for the power amplifier transistor, provides adaptive biasing to compensate for transistor non-idealities, and improves power added efficiency. By consolidating these functions into a single circuit block, the patent reduces overall system complexity while achieving multiple performance benefits.
3Ease of manufacture
If short channel metal oxide semiconductor transistor is used in power amplifier, then device integration improves, but non-idealities such as gain variation and current variation increase
Solution Approach 1:
The patent implements a self-service mechanism where the Wilson current mirror automatically adjusts the gate voltage of the short channel MOS transistor based on its own drain voltage. This self-adjusting mechanism compensates for non-idealities inherent in short channel transistors, such as gain variation and current variation, without requiring external intervention or complex control circuits.
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 generates the power amplifier supply voltage based on an envelope of the RF signal. The power amplifier includes a field-effect transistor (FET) for amplifying the RF signal, and a current mirror including an input that receives a reference current and an output connected to the power amplifier supply voltage. An internal voltage of the current mirror is used to bias the gate of the FET to compensate the FET for changes in the power amplifier supply voltage arising from envelope tracking.