RF Power Amplifier Envelope Tracking Delay Offset Calibration
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Solution Overview
Problem
Open loop envelope tracking systems for radio frequency power amplifiers face challenges in calibrating group delay misalignment between the modulated power amplifier supply voltage and the modulated signal, leading to spectrum and error vector magnitude degradation, and existing calibration techniques are not reliable or repeatable due to offset errors and limited sensitivity in detecting delay mismatches.
Innovation Solution
An open loop envelope tracking system calibration technique that involves measuring output powers at different delay periods, adjusting these periods to maximize sensitivity, and determining a calibrated fine tuning delay offset to align the modulated power amplifier supply voltage with the modulated signal, using a digital baseband circuit, envelope tracker power converter, and controller circuitry to achieve optimal alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration techniques based on maximizing output power are used, then the calibration process is simple, but the measurement precision and reliability are insufficient due to offset errors and limited sensitivity
Solution Approach 1:
The calibration process is divided into two distinct stages: coarse calibration using output power maximization to establish an initial delay offset, and fine calibration using sensitivity-based optimization to achieve precise delay alignment. This segmentation allows each stage to focus on specific requirements, improving overall measurement precision without overwhelming system complexity.
Solution Approach 2:
The coarse calibration stage performs preliminary adjustment by maximizing output power to establish an initial delay offset before conducting the fine calibration stage. This preliminary action reduces the search space for the fine calibration algorithm, making the overall process more efficient and reliable.
2Reliability
If the delay mismatch between modulated power amplifier supply voltage and modulated signal is not calibrated, then the system operation is simple, but spectrum degradation and error vector magnitude degradation occur
Solution Approach 1:
The system incorporates feedback mechanisms where the measured output power and sensitivity information from the power amplifier are fed back to the controller circuitry. This feedback enables iterative adjustment of delay offsets until optimal alignment is achieved, ensuring reliable spectrum and error vector magnitude performance.
Solution Approach 2:
The calibration system uses the device's own internal resources - the power amplifier, detector, and controller circuitry already present in the system - to perform self-calibration without requiring external specialized equipment. This self-service approach achieves reliable performance while minimizing additional device complexity.
3Measurement precision
If detectors with high sensitivity to delay mismatch are used, then the measurement precision improves, but the device complexity and cost increase
Solution Approach 1:
Instead of using specialized high-sensitivity detectors, the system achieves high measurement precision by changing the operating parameters - specifically by operating at delay offsets where the power amplifier exhibits maximum sensitivity to delay changes. This parameter-based approach extracts maximum precision from ordinary detectors.
Solution Approach 2:
The system leverages the inherent characteristics of the power amplifier itself - its natural sensitivity variations with delay offset - to provide the measurement function. The power amplifier's own response characteristics are used as the measurement mechanism, eliminating the need for specialized external detectors.
Data Source
AI summary
An open loop envelope tracking system calibration technique and circuitry are proposed. A radio frequency power amplifier receives a modulated signal. An envelope tracker power converter generates a modulated power amplifier supply voltage for the radio frequency power amplifier based on a control signal derived from the modulated signal. A first output power and a second output power of the radio frequency power amplifier are measured when the control signal is respectively delayed by a first delay period and a second delay period. A sensitivity of the output power of the radio frequency power amplifier is near a maximum near the first delay period and the second delay period. The first delay period and/or the second delay period are adjusted until the first output power substantially equals the second output power. The first delay period and the second delay period are used to obtain a calibrated fine tuning delay offset.