Power Amplifier Digital Pre-Distortion Without Real-Time Feedback
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Solution Overview
Problem
High-frequency power amplifiers face a trade-off between efficiency and linearity, with increasing efficiency leading to amplitude and phase distortion, and existing feedback-based pre-distortion techniques require significant processing power and are incomplete for multiple amplifiers, complicating equipment and calibration.
Innovation Solution
A circuit arrangement with a built-in test circuit and signal conditioner performs feed-forward pre-distortion of the digital input signal based on distortion information, eliminating the need for real-time feedback and allowing independent adjustment for each amplifier, using a common signal source and signal conditioner to map the input signal onto a pre-distorted version.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If feedback-based pre-distortion technique is used to maintain linearity, then linearity is improved, but processing power requirement and device complexity increase significantly
Solution Approach 1:
The patent applies preliminary action by performing pre-distortion in the digital domain before the signal reaches the power amplifier. The processor calculates corrected amplitude and phase values for each input signal value and stores them in lookup tables. This advance preparation eliminates the need for complex real-time feedback processing, as the distortion compensation is already embedded in the lookup tables generated during calibration.
Solution Approach 2:
The patent replaces the mechanical/physical feedback system with a digital computational approach. Instead of using analog feedback circuits and real-time subtractors that require significant processing power, the system uses pre-calculated digital lookup tables that can be queried efficiently. This substitution of physical feedback mechanisms with digital pre-computation dramatically reduces the processing burden during operation.
2Loss of energy
If efficiency of power amplifier is increased, then power consumption is reduced, but linearity deteriorates causing amplitude and phase distortion
Solution Approach 1:
The patent applies preliminary anti-action by pre-compensating for the distortion that will occur when the amplifier operates at high efficiency. During calibration, the system measures the actual distortion characteristics of the amplifier and calculates correction values that counteract this distortion. These correction values are stored in lookup tables, allowing the amplifier to maintain linearity even when operating at high efficiency levels without feedback.
Solution Approach 2:
The patent uses feedback during the calibration phase to characterize amplifier distortion. The processor generates test signals, measures the amplifier's output including its distortion, and uses this feedback information to calculate appropriate pre-distortion correction values. This calibration feedback enables the system to adapt to each amplifier's specific distortion characteristics, allowing high-efficiency operation with maintained linearity.
3Device complexity
If one single digital pre-distortion function is used for multiple amplifiers, then device complexity is reduced, but pre-distortion completeness deteriorates
Solution Approach 1:
The patent applies local quality by allowing each amplifier to have its own specific pre-distortion lookup tables tailored to its individual distortion characteristics. During calibration, each amplifier is tested independently and its specific distortion profile is measured. The processor then generates customized lookup tables for each amplifier based on its unique characteristics. This per-amplifier customization ensures optimal pre-distortion accuracy for each device while using a standardized calibration and processing framework.
4Manufacturing precision
If feedback-based pre-distortion is implemented for each antenna element, then linearity is maintained, but processing power and equipment complexity increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing distortion correction values in lookup tables for each antenna element's amplifier during calibration. Each lookup table contains pre-computed amplitude and phase correction values specific to that amplifier's characteristics. During operation, the system simply queries these pre-prepared tables rather than performing complex real-time calculations or feedback processing for each antenna element, dramatically reducing processing requirements while maintaining per-element linearity.
Data Source
AI summary
Techniques (implemented in circuit arrangements, methods, computer instructions) are disclosed which permit digital pre-distortion for amplifiers. A common signal source provides a common analog signal from a digital input signal; a plurality of amplifiers amplifies a split signal which is a split version of the common analog signal; a built-in test circuit is configured to provide distortion information associated to distortion affecting the amplifier. The common signal source implements a signal conditioner to perform, in a signal path of the digital input signal, a feed-forward pre-distortion of the digital input signal according to a pre-distortion relationship mapping the digital input signal onto a pre-distorted version. The signal conditioner is configured to adjust the pre-distortion relationship in dependence on the distortion information.