RF Front-End Matching Circuit for Intra-Band IMD Suppression
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Solution Overview
Problem
Intra-band carrier aggregation in communication systems leads to intermodulation distortions (IMDs) that cannot be removed by existing transmission filters, causing issues with spectrum emission masks and spurious emissions, particularly due to low linearity in power amplifier circuits.
Innovation Solution
A front-end circuit that switches between intra-band carrier aggregation mode and single mode, using a matching circuit to increase insertion loss in the frequency band of intermodulation distortions, thereby suppressing their power by mismatching impedance in the signal path between the antenna and power amplifier circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple transmission waves are transmitted through a single power amplifier circuit and transmission filter to achieve carrier aggregation, then communication rate is increased, but intermodulation distortions occur that cannot be removed by the transmission filter
Solution Approach 1:
The invention segments the signal path by introducing a separate detection path with a detection filter that has different frequency characteristics from the transmission filter. This allows IMD components to be detected separately and enables independent compensation control, resolving the contradiction by treating the transmission and detection functions as separate segments.
Solution Approach 2:
The invention introduces an intermediary detection system consisting of a detection filter, level detection circuit, and control circuit that mediates between the power amplifier output and the transmission filter input. This intermediary detects IMD components and generates control signals to adjust transmission power, thereby eliminating harmful IMD without directly modifying the transmission filter.
2Reliability
If transmission power is decreased to reduce intermodulation distortion, then spectrum emission mask specifications are satisfied, but communication efficiency is reduced
Solution Approach 1:
The invention implements a feedback control mechanism where the detection filter detects IMD components in real-time, the level detection circuit measures their power levels, and the control circuit adjusts transmission power based on these measurements. This closed-loop feedback system maintains spectrum emission mask compliance while maximizing communication efficiency by dynamically optimizing transmission power rather than uniformly reducing it.
Solution Approach 2:
Instead of uniformly decreasing transmission power across all frequencies, the invention applies partial action by selectively compensating only for frequency components where IMD occurs. The control circuit adjusts transmission power specifically to reduce IMD components while maintaining optimal power levels for legitimate signal transmission, thus preserving communication efficiency.
3Adaptability or versatility
If a transmission filter with a wide pass band is used to accommodate multiple component carriers, then carrier aggregation is enabled, but intermodulation distortion components within the pass band cannot be removed
Solution Approach 1:
The invention segments the filtering function by using a detection filter with different frequency characteristics from the transmission filter. The detection filter is specifically designed to pass IMD frequency components while the transmission filter maintains its wide pass band for carrier aggregation, allowing separate detection and compensation of IMD without limiting communication bandwidth.
Solution Approach 2:
The invention applies local quality by making the detection filter have specialized frequency characteristics tailored for detecting specific IMD components, while the transmission filter maintains its general-purpose wide pass band. This localized optimization of filter characteristics enables the detection system to identify and compensate IMD without compromising the transmission system's carrier aggregation capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively reduces intermodulation distortions within the communication band without requiring complex control processes, ensuring compliance with spectrum emission mask specifications by increasing insertion loss of IMDs in the intra-band carrier aggregation mode.
Implementation Method 1
using a matching circuit to increase insertion loss in the frequency band of intermodulation distortions, thereby suppressing their power by mismatching impedance in the signal path
Data Source
AI summary
A front-end circuit includes a power amplifier circuit configured to amplify power of multiple transmission waves having different frequency bands, a transmission filter provided between the power amplifier circuit and an antenna and configured to pass a predetermined transmission frequency band of an output signal of the power amplifier circuit, a switch provided between the power amplifier circuit and the antenna, and a matching circuit. In accordance with switching of whether the matching circuit is connected, an insertion loss in a frequency band of an intermodulation distortion within a communication band in an intra-band carrier aggregation mode is increased as compared to an insertion loss in a frequency band of an intermodulation distortion within the communication band in a single mode.