RF Power Amplifier Predistortion for Fast Power Transients
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Solution Overview
Problem
Existing RF power amplifier linearizers achieve good adjacent channel leakage ratio (ACLR) performance only across a limited range of output powers, failing to effectively linearize the output response over a wide range, especially in the presence of fast power transient waveforms.
Innovation Solution
An RF power amplifier linearizer that dynamically adapts multiple sets of parameter values, including coefficient vectors, tailored for specific output power ranges, using a fast attack/slow decay filter to track input power changes and minimize variance, thereby achieving improved ACLR performance across a broader power range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single set of coefficients is used for all operating power levels, then the device complexity is reduced, but the ACLR performance deteriorates across a wide range of output powers
Solution Approach 1:
The patent divides the operating power range into multiple segments (power levels), with each segment having its own optimized coefficient set. The power amplifier operation is segmented into different power ranges, and the appropriate coefficient set is selected based on the current operating segment, thereby achieving good ACLR performance across the entire wide power range while managing complexity through structured organization.
Solution Approach 2:
The patent implements dynamic selection of coefficient sets based on the current operating power level. The system transitions between different coefficient sets as the power amplifier operates across different power ranges, making the linearization adaptive and dynamic rather than static. This dynamic approach ensures optimal ACLR performance at each power level while responding to changing operating conditions.
2Reliability
If multiple sets of parameter values are maintained for different output power ranges, then the ACLR performance is improved across a wide range, but the device complexity increases
Solution Approach 1:
The multiple parameter sets are organized into distinct segments corresponding to different power ranges. Each segment contains parameter sets optimized for specific operating conditions, allowing the system to achieve wide-range ACLR performance while managing complexity through systematic segmentation and organized storage of parameter sets.
Solution Approach 2:
The patent changes the parameters (coefficient values) based on the operating power level. By maintaining multiple sets of parameter values and selecting the appropriate set according to the current power range, the system achieves improved ACLR performance across a wide power range. The parameter changes are systematic and controlled, balancing performance improvement with manageable complexity.
3Speed
If a fast attack/slow decay filter is used to track input power changes, then the response speed to power transients is improved, but the measurement precision may be affected
Solution Approach 1:
The filter dynamically adjusts its response characteristics using fast attack and slow decay time constants. During power transients, the fast attack portion enables rapid tracking of power changes, while the slow decay portion provides smoothing during steady-state operation. This dynamic filtering approach balances response speed and measurement precision adaptively based on operating conditions.
Solution Approach 2:
The filter operates with different time constants depending on the state of power change. The fast attack/slow decay characteristic creates a periodic-like response pattern where the filter responds quickly to rising power transients and decays slowly during falling edges, enabling the system to capture fast power changes while maintaining stable measurements during steady states.
Data Source
AI summary
An apparatus and a method select and use parameter values for an RF power amplifier linearizer to pre-distort the input signals of a power amplifier, so as to achieve a linear output response in the power amplifier. The apparatus and the method select from a number sets of parameter values, each set of parameter values corresponding to a different output power range of the power amplifier. The set of parameters include a coefficient vector tailored for the particular output power range for that set. The power amplifier input power is repeatedly measured and filtered at various time intervals. The input power measurements may be filtered by a fast attack/slow decay filter, which follows the peaks of the measurements under operation of the fast attack portion of the filter and provides a low variance during operation of the slow decay portion of the filter. The coefficient values for the predistortion linearization of the power amplifier is adapted dynamically, in response to changes in the input power level of the power amplifier. In one embodiment, hysteresis is used to reduce the rate at which the predistortion linearizer hops between two sets of the parameter values. Using the apparatus and the method, good ACLR across a wide range of power amplifier output power is achieved. Such characteristics are particularly advantageous in a system in which waveforms having fast power transients are present.