Low-Bandwidth Predistortion for Nonlinear RF Filter Linearity
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Solution Overview
Problem
Non-linear characteristics in radio frequency filters used in communication networks lead to manufacturing challenges, cost issues, and communication quality degradation, particularly in high and low power base stations and user equipment devices, due to the non-linearity of filters like cavity, ceramic, and miniature filters.
Innovation Solution
The implementation of predistortion techniques, including adaptive digital and analog predistortion, to compensate for the non-linearity of filters, using a system that includes a power amplifier, digital-to-analog converter, and a predistorter configured by an adaptor based on feedback signals, effectively treating the non-linear filter as a linear one.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If cavity filters are used in high power base stations to handle high output power, then the filter can handle the high power, but the manufacturing cost increases due to low first round production yield (around 60%)
Solution Approach 1:
The patent applies predistortion processing to the input signal before it enters the non-linear filter, proactively compensating for the filter's non-linear characteristics. This preliminary action allows the use of lower-cost filters while maintaining linear output performance, resolving the contradiction between power handling and manufacturing cost.
Solution Approach 2:
The patent converts the harmful non-linear characteristics of inexpensive filters into a manageable parameter through predistortion. By intentionally pre-distorting the input signal, the system transforms what would be a defect into a controllable feature, enabling cost-effective high-power filter solutions.
2Reliability
If cavity filters are used to provide desired linearity, then the filter provides good linearity, but the filter becomes very large and heavy
Solution Approach 1:
The patent replaces the mechanical solution (large cavity filter) with an electronic signal processing solution (predistorter). Instead of using a physically large filter to achieve linearity, the system uses digital or analog predistortion circuitry to compensate for non-linearities, enabling the use of compact filters while maintaining linearity.
3Volume of moving object
If ceramic filters and monoblock filters are used in low power base stations to reduce size, then the filter size is reduced, but the filter does not provide desired linearity when operating at higher power (above 5 W)
Solution Approach 1:
The predistorter pre-compensates for the non-linear characteristics of compact ceramic and monoblock filters before the signal enters these filters. This preliminary signal processing enables these small filters to operate at higher power levels (5-20 W) while maintaining acceptable linearity, resolving the contradiction between size and reliability.
4Volume of moving object
If miniature filters (SAW, FBAR, BAW) are used in user equipment devices to reduce size, then the device size is reduced, but the filter operates in its non-linear region at peak power levels
Solution Approach 1:
The patent replaces the reliance on passive filter linearity with active predistortion signal processing. This substitution allows miniature filters to be used in user equipment at peak power levels without communication quality degradation, as the predistorter compensates for the filters' non-linear operation.
5Reliability
If predistortion is applied to compensate for filter non-linearity, then linearity is maintained over wider power range, but the system complexity increases
Solution Approach 1:
The patent introduces a predistorter as an intermediary component between the signal source and the non-linear filter. This mediator pre-processes the signal to compensate for upcoming non-linearities, maintaining linearity without requiring fundamental changes to the filter or transmitter architecture, thus managing complexity effectively.
Data Source
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AI summary
Systems and methods for compensating for non-linearity of a non-linear subsystem using predistortion are disclosed. In one embodiment, a system includes a non-linear subsystem and a predistorter configured to effect predistortion of an input signal of the non-linear subsystem such that the predistortion compensates for a non-linear characteristic of the non-linear subsystem. In addition, the system includes a narrowband filter that filters a feedback signal that is representative of an output signal of the non-linear subsystem to provide a filtered feedback signal, and an adaptor that adaptively configures the predistorter based on the filtered feedback signal and a reference signal that is representative of an input signal of the non-linear subsystem. By utilizing the filtered feedback signal, rather than the feedback signal, a complexity, and therefore, cost of the adaptor is substantially reduced.