Envelope Tracking Calibration for Wireless Transmitter ACLR Compliance
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Solution Overview
Problem
Envelope tracking in wireless communication transmitters faces challenges in maintaining time alignment between the transmission signal path and the envelope signal path, leading to non-linearity and instantaneous waveform clipping, which affects Adjacent Channel Leakage Ratio (ACLR) compliance.
Innovation Solution
A calibration method that involves transmitting both a normal and a comparison envelope signal to measure corresponding ACLRs, calculating time misalignment, and adjusting the delay offset to ensure accurate alignment between the transmission and envelope signal paths, thereby maintaining linearity and compliance with ACLR requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If envelope tracking is implemented to improve power amplifier efficiency, then power added efficiency is improved, but linearity deteriorates due to removal of bias overhead
Solution Approach 1:
The patent applies preliminary action by performing time alignment calibration before actual envelope tracking operation. The calibration process measures ACLR in both normal and comparison modes to determine time misalignment, then adjusts delay offsets to align the transmission and envelope signal paths beforehand, ensuring linearity is maintained during efficiency-critical operation.
Solution Approach 2:
The patent implements feedback by measuring ACLR performance and using this measurement to adjust the time alignment between signal paths. The system continuously monitors ACLR in normal and comparison modes, calculates time misalignment from the difference, and applies delay adjustments to maintain optimal linearity while preserving power efficiency benefits.
2Reliability
If digital pre-distortion is added to maintain linearity in envelope tracking, then linearity is improved, but device complexity increases
Solution Approach 1:
The patent applies parameter changes by adjusting the time alignment parameter (delay offset) between the transmission and envelope signal paths. Instead of adding complex pre-distortion circuitry, the system modifies the timing parameter to achieve proper synchronization, thereby maintaining linearity through a simpler parameter adjustment rather than structural complexity increase.
3Reliability
If time alignment calibration is performed to maintain linearity, then ACLR performance is improved, but measurement and calibration time increases
Solution Approach 1:
The patent applies partial action by performing calibration using only two specific measurement modes (normal and comparison modes) rather than exhaustive calibration across all possible operating conditions. This partial calibration approach achieves sufficient time alignment for ACLR compliance without requiring excessive calibration time, balancing performance with efficiency.
Data Source
AI summary
An apparatus for envelope tracking calibration for use in a wireless communication is provided. The apparatus includes a transmission signal path configured to carry a transmission signal to an antenna. An envelope signal path configured to feed an envelope signal with an envelope tracking power amplifier. A controller is configured to transmit a normal envelope signal being generated in a normal operation mode and measure a first Adjacent Channel Leakage Ratio (ACLR) corresponding to the normal envelope signal. The controller is further configured to transmit a comparison envelope signal being generated in a comparison operation mode and measure a second ACLR corresponding to the comparison envelope signal. The controller is configured to calculate a time misalignment between the transmission signal path and the envelope signal path based on a difference between the first and second ACLRs.