DLL Phase Measurement for RF Power Amplifier AMPM Correction
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Solution Overview
Problem
Polar modulation systems in RF communications face challenges due to Amplitude Modulation-to-Phase Modulation (AMPM) distortion, which degrades spectral purity and Error Vector Magnitude (EVM), and requires real-time calibration to account for changes caused by temperature, age, and other factors.
Innovation Solution
The implementation of delay locked loop (DLL) circuitry to measure and correct AMPM distortion in RF power amplifiers during both factory calibration and real-time operation by determining phase differences between input and output signals at varying amplitudes, using a reference clock signal and feedback signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If polar modulation is used to improve power amplifier efficiency, then efficiency is greatly improved, but unwanted phase components are created causing AMPM distortion that degrades spectral purity and EVM
Solution Approach 1:
The patent applies preliminary anti-action by pre-distorting the phase modulation component before it enters the power amplifier. The pre-distortion circuitry introduces an opposite phase distortion that compensates for the AMPM distortion generated by the power amplifier, thereby reducing the net distortion at the output while maintaining the efficiency benefits of polar modulation
2Reliability
If AMPM pre-distortion circuitry is implemented to reduce AMPM distortion, then spectral purity and EVM are improved, but the distortion changes with temperature, age, and other factors requiring real-time re-calibration
Solution Approach 1:
The patent implements feedback by measuring the actual phase difference between the input and output signals of the power amplifier and using this measurement to update the pre-distortion parameters. The delay-locked loop circuitry continuously monitors the phase distortion and adjusts the pre-distortion circuitry accordingly, enabling the system to adapt to changes in temperature, age, and other environmental factors while maintaining high spectral purity and EVM performance
3Measurement precision
If phase difference measurements are performed at different amplitudes to determine AMPM distortion, then accurate distortion characterization is achieved, but measurement time and complexity increase
Solution Approach 1:
The patent applies periodic action by performing phase difference measurements at multiple different amplitudes during a calibration process to fully characterize the AMPM distortion across the operating range. Once characterized, the system uses periodic updates at key amplitude points to maintain accuracy without requiring continuous full-range measurements, thus achieving high measurement precision while minimizing time loss during normal operation
Data Source
AI summary
The present disclosure relates to RF circuitry having delay locked loop (DLL) circuitry that may be used to measure amplitude modulation-to-phase modulation (AMPM) distortion of an RF power amplifier during factory calibration or during real time operation of the RF circuitry. During a calibration mode, the DLL circuitry may be calibrated using a reference clock signal. During a phase measurement mode, the DLL circuitry may use the reference clock signal, which is representative of an RF input signal to the RF power amplifier, and a feedback signal, which is representative of an RF output signal from the RF power amplifier, to measure a phase difference between the RF input signal and the RF output signal. By measuring the phase difference at different amplitudes of the RF output signal, the AMPM distortion of the RF power amplifier may be determined and used to correct for the AMPM distortion.