Open-Loop Envelope Tracking Calibration for PA Load Pre-Distortion
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Solution Overview
Problem
Open loop envelope tracking (ET) modulators in wireless terminals face stability issues due to varying power amplifier loads, leading to performance degradation without accurate load variation tracking, which is challenging without feedback paths.
Innovation Solution
Implementing a PA load variation pre-distortion method that dynamically senses and compensates for load variations during factory calibration, using a PA supply sensing system to update parameters and generate a pre-distortion compensation signal, ensuring the PA supply voltage matches the reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If an open loop ET modulator is used to avoid feedback loop stability issues, then stability is improved, but PA load variations cause varying voltage reference inputs that degrade system performance
Solution Approach 1:
The patent applies preliminary action by pre-characterizing the PA load variations during factory calibration and storing compensation data in a lookup table. This pre-computed compensation information is then used during operation to correct for load variations without requiring real-time feedback, thus maintaining stability while improving performance consistency.
2Measurement precision
If factory calibration with PA load variation pre-distortion is implemented, then frequency response accuracy is improved, but device complexity increases due to additional calibration procedures and storage requirements
Solution Approach 1:
The patent performs the complex calibration and characterization work during factory calibration, storing the results in a lookup table. This shifts the complexity from the operational phase to the manufacturing phase, allowing the device to operate with simple table lookups rather than complex real-time calculations.
Solution Approach 2:
The patent creates a simplified model of the PA load variations through factory calibration and stores it as a lookup table. This copy of the load variation characteristics allows the system to compensate for variations without needing the actual complex PA model during operation.
3Manufacturing precision
If accurate PA load variation information is obtained during dynamic signal excitation, then pre-distortion effectiveness is improved, but measurement and detection difficulty increases
Solution Approach 1:
The patent measures and characterizes the PA load variations during factory calibration when the system is under controlled test conditions. This preliminary measurement captures the load variation characteristics that would occur during dynamic signal excitation, storing them for later use without needing to perform difficult real-time measurements during operation.
Data Source
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AI summary
A method for implementing envelope tracking (ET), the method comprising switching from a receiver (Rx) radio frequency (RF) path to a supply sensing path during factory calibration, sensing the power amplifier (PA)'s supply voltage via the supply sensing path, comparing the PA's supply voltage to a corresponding reference supply voltage, determining the difference between the PA's supply voltage and the corresponding reference supply voltage, and updating one or more parameters used to perform a PA load pre-distortion during factory calibration, wherein the PA load pre-distortion is used to match the PA's supply voltage to the corresponding reference supply voltage.