Envelope-Tracked Power Amplifier Linearity via IMD Compensation
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Solution Overview
Problem
Power amplifiers in mobile devices face challenges in achieving high linearity and efficiency, especially when using CMOS processing, which can result in poor linearity and increased power consumption, particularly when employing envelope tracking that introduces nonlinearities and intermodulation distortion.
Innovation Solution
The implementation of an envelope tracker characterization method that includes providing input signals to a power amplifier, generating a supply voltage signal based on the envelope of these signals, delaying the signals to measure intermodulation distortion, calculating the IMD phase angle, and using distortion compensation circuits to adjust the power amplifier's performance, thereby improving linearity and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If envelope tracking is used to reduce power consumption, then power efficiency is improved, but intermodulation distortion increases
Solution Approach 1:
The patent measures the IMD phase angle caused by envelope tracking and uses this information to calculate compensation parameters. The harmful intermodulation distortion is converted into a measurable parameter that guides the compensation process, transforming the problem into a solution pathway.
Solution Approach 2:
The patent adjusts delay values and gain values as compensation parameters to counteract the intermodulation distortion. By changing these parameters dynamically based on measured IMD characteristics, the system maintains power efficiency while reducing distortion.
2Manufacturing precision
If distortion compensation is applied, then linearity is improved, but device complexity increases
Solution Approach 1:
The patent introduces an intermediary measurement process that characterizes the IMD phase angle between the power amplifier and envelope tracker. This intermediary step provides quantitative data that simplifies the compensation process, making it more manageable despite the added complexity of compensation circuits.
Solution Approach 2:
The patent implements a feedback mechanism where the measured IMD phase angle informs the calculation of compensation parameters. This closed-loop approach allows the system to automatically adjust delay and gain values to maintain optimal linearity without requiring complex manual tuning.
3Measurement precision
If delay adjustment is used to measure IMD, then measurement precision is improved, but time consumption increases
Solution Approach 1:
The patent uses partial delay adjustments at specific values to measure intermodulation distortion rather than requiring complete characterization across all possible delays. This partial action approach achieves sufficient measurement precision while reducing the total time required for characterization.
Data Source
AI summary
Envelope tracking can be employed to reduce power consumption of a power amplifier, but envelope tracking can introduce nonlinearities to a power amplifier. These nonlinearities can manifest themselves as noise at the output of the power amplifier. Embodiments described herein provide techniques for characterizing a parameter indicative of power amplifier noise when envelope tracking is employed. Measurement of this parameter can permit power amplifier designers to decide whether to forgo envelope tracking if a power amplifier is too susceptible to such noise, redesign the power amplifier to improve compatibility with envelope tracking, or to employ distortion compensation circuitry to reduce the noise output by the power amplifier. Counterintuitively, this distortion compensation circuitry may involve increasing the power, such as the envelope tracking power supply. However, increasing the power may be a desirable trade-off for increased linearity.