Linearized RF Transmitter Using Predistortion for PA Distortion
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Solution Overview
Problem
Power amplifier circuits in wireless local area network systems experience distortion due to large swings in output power levels, leading to signal transmission errors and reduced communication quality, which is exacerbated by integration with other RF transmitter circuitry and limitations in semiconductor fabrication technologies.
Innovation Solution
A method and system for a linearized transmitter that utilizes a multiband RF transmitter with a demarcation point dividing the transmitter chain into a transconductance stage and a gain stage, generating multiple RF output signals using a single transconductance stage and multiple gain stages, and employing digital predistortion to compensate for AM-AM and AM-PM distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If power amplifier circuits operate over a wide range of frequencies with large swings in output power levels, then the transmitter can support multiple WLAN standards and modulation schemes, but distortion increases leading to signal transmission errors
Solution Approach 1:
The transmitter chain is divided into multiple stages including a first power amplifier stage and a second power amplifier stage, each operating at different power levels. This segmentation allows the system to handle wide power swings by distributing amplification across stages, reducing distortion in each individual stage while maintaining overall high output power capability and supporting multiple WLAN standards.
Solution Approach 2:
Digital predistortion is applied to the input signal before amplification to pre-compensate for expected non-linear distortion. This preliminary action counteracts the distortion that will occur during amplification, allowing the power amplifier to operate efficiently over wide frequency ranges and power levels while maintaining signal accuracy and reducing transmission errors.
2Device complexity
If power amplifier circuits are integrated with other RF transmitter circuitry, then device complexity is reduced, but distortion performance deteriorates due to fabrication technology limitations
Solution Approach 1:
Different portions of the power amplifier circuit are implemented using different fabrication techniques optimized for their specific functions. Critical linearization components are implemented with higher precision while less sensitive components use standard CMOS processes. This local quality approach maintains good distortion performance even when integrated with other RF circuitry on the same chip.
Solution Approach 2:
The power amplifier circuit combines multiple transistor types and circuit topologies within a single integrated device. By using composite circuit structures with different characteristics, the design achieves both integration with other RF circuitry and acceptable distortion performance, leveraging the strengths of different circuit configurations to compensate for fabrication limitations.
3Reliability
If digital predistortion is applied to compensate for AM-AM and AM-PM distortion, then linearity is improved, but system complexity increases
Solution Approach 1:
The system uses feedback from the output signal to adjust the predistortion parameters dynamically. By monitoring the actual output and adjusting the predistortion accordingly, the system achieves high linearity without requiring overly complex open-loop predistortion circuits. The feedback mechanism allows simpler circuitry to achieve better performance through closed-loop optimization.
Solution Approach 2:
The predistortion characteristics are made adjustable through programmable parameters that can be optimized for different operating conditions, frequency bands, and power levels. This parameter adaptability allows a single predistortion circuit to handle multiple WLAN standards and modulation schemes effectively, reducing the need for multiple dedicated circuits and thereby limiting the increase in system complexity.
Data Source
AI summary
Disclosed are various embodiments for transmitting radio frequency signals. A radio frequency transmitter may be configured to generate an analog signal comprising an in-phase component and a quadrature-phase component. The in-phase component and the quadrature-phase component of the analog signal may be provided to multiple radio frequency processing chains. One of the radio frequency processing chains may generate an output radio frequency signal based on the in-phase component and the quadrature-phase component.