Polar Modulated RF Transmitter Phase Distortion Calibration
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Solution Overview
Problem
Polar modulated RF transmitters face challenges in maintaining RF output power tolerances, Error Vector Magnitude (EVM) specifications, and Output Radio Frequency Spectrum (ORFS) requirements due to phase distortion and amplitude non-linearities, which affect the reliability and efficiency of digital information encoding.
Innovation Solution
The method employs amplitude pre-distortion to compensate for phase distortion (AMPM compensation) and amplitude non-linearities (AMAM compensation), using calibration constants determined by measuring phase distortion and amplitude non-linearities, which are applied during normal operation to ensure compliance with RF output power, EVM, and ORFS specifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If large signal amplitude modulation is used to maximize information encoding, then the amount of digital information that can be encoded is improved, but phase distortion and amplitude non-linearities worsen, affecting EVM and RF output power tolerances
Solution Approach 1:
The patent applies pre-distortion techniques where the amplitude and phase characteristics of the modulator are measured and compensated in advance. Calibration constants are determined by measuring the actual amplitude response and phase distortion, then applying inverse corrections before modulation. This preliminary action prevents phase distortion and amplitude non-linearities from degrading EVM performance while maintaining high information encoding capacity through large signal amplitude modulation.
2Loss of information
If large signal amplitude modulation is used to maximize information encoding, then the amount of digital information that can be encoded is improved, but RF output power tolerances worsen due to amplitude non-linearities
Solution Approach 1:
The patent measures the amplitude response of the modulator across different amplitude levels and determines calibration constants that compensate for non-linearities in advance. During operation, these pre-determined constants ensure that RF output power remains within specified tolerances even when using large signal amplitude modulation for high-capacity information encoding.
3Reliability
If calibration constants are determined by measuring phase distortion and amplitude non-linearities, then EVM and RF output power compliance are improved, but device complexity increases due to additional calibration and measurement requirements
Solution Approach 1:
The patent enables the modulator to self-calibrate by measuring its own amplitude response and phase distortion characteristics. The system determines its own calibration constants through internal measurements rather than requiring external calibration equipment, thereby improving EVM and ORFS compliance while minimizing the increase in device complexity.
4Reliability
If pre-distortion calibration is implemented to compensate for phase distortion and amplitude non-linearities, then transmitter performance meets stringent specifications, but ease of operation worsens due to additional calibration steps
Solution Approach 1:
The modulator performs self-calibration by automatically measuring its own amplitude response and phase distortion and determining the necessary calibration constants without requiring manual intervention or complex external calibration equipment. This self-service approach ensures compliance with stringent transmitter specifications while maintaining ease of operation.
Data Source
AI summary
The present invention is a method for calibrating a phase distortion compensated polar modulated RF transmitter, which uses amplitude pre-distortion to compensate for phase distortion, called AMPM compensation. Some embodiments of the present invention may include a method for calibrating polar modulated RF transmitters that use amplitude pre-distortion to compensate for amplitude non-linearities, called AMAM compensation. The AMPM and AMAM compensations may enable the polar modulated RF transmitter to conform to RF output power tolerances, meet EVM specifications, and meet ORFS requirements. The pre-distortion calibration methods may be used to determine calibration constants by measuring phase distortion and amplitude non-linearities. During normal operation, the calibration constants may be used to provide the AMPM and AMAM compensations.