Adjacent Channel Interference Detection Using IQ Rotation Imbalance
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Solution Overview
Problem
Existing methods for detecting adjacent channel interference in FM radio receivers, especially when integrating components onto a single LSI chip, face challenges such as increased circuit size, the need for dedicated analog cells, and insufficient detection sensitivity during digital signal processing.
Innovation Solution
An adjacent channel interference detection apparatus that uses a local oscillation unit generating 90-degree phase-shifted signals, mixer units, low pass filters, sign inversion detection units, a rotation judgment unit, counter, and detection unit to determine signal point rotations on the IQ plane, allowing for high sensitivity detection without requiring a dedicated filter or large analog cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a delta-sigma AD converter is used to digitize the IF signal, then digital signal processing can be performed, but a dedicated filter with steep characteristic is required to extract the frequency component, causing significant increase in circuit size
Solution Approach 1:
The patent extracts only the necessary function for adjacent channel interference detection from the complete signal processing chain. Instead of requiring a full steep characteristic filter to process the entire IF signal, the invention extracts and processes only the specific frequency component relevant to interference detection, thereby reducing the filter complexity and circuit size while maintaining digital signal processing capability.
Solution Approach 2:
The patent segments the signal processing function into two parts: the main IF signal processing path and the separate adjacent channel interference detection path. The detection path uses a simplified filter structure that only needs to handle the specific interference frequency components, rather than requiring the main path to have steep filtering characteristics. This segmentation allows digital processing while reducing overall circuit complexity.
2Measurement precision
If an analog waveform shaping circuit is used to binarize the IF signal before counting, then frequency counting can be performed, but a dedicated analog cell and greater placement constraint are required on the LSI substrate
Solution Approach 1:
The patent replaces the analog waveform shaping circuit with a digital signal processing approach. Instead of using analog components to binarize the IF signal before counting, the invention performs the binarization and frequency counting operations in the digital domain after AD conversion. This substitution eliminates the need for dedicated analog cells and reduces placement constraints on the LSI substrate while maintaining frequency counting accuracy.
3Adaptability or versatility
If the FM demodulated signal smoothing structure is used for digital processing, then LSI integration is possible, but detection sensitivity is insufficient
Solution Approach 1:
The patent creates a composite detection structure that combines multiple processing stages: AD conversion, digital filtering with optimized characteristics, and frequency counting. This composite approach integrates the advantages of digital processing (LSI compatibility) while compensating for the sensitivity limitations through the combined effect of the digital filter and counter, achieving both integration and high detection sensitivity.
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
This approach enables high detection sensitivity with a simple circuit structure, suitable for LSI integration, reducing circuit size and eliminating the need for dedicated filters or analog cells, while effectively identifying adjacent channel interference.
Implementation Method 1
a local oscillation unit that generates two signals of a predetermined frequency in a free-running state, the two signals of the predetermined frequency being different in phase from each other by 90 degrees
Implementation Method 2
two mixer units that mix an input signal respectively with the two signals of the predetermined frequency generated by the local oscillation unit
Implementation Method 3
two low pass filter units respectively connected to outputs of the two mixer units
Data Source
AI summary
To provide an adjacent channel interference detection apparatus having high detection sensitivity and suitable for LSI integration in a small circuit size. The adjacent channel interference detection apparatus (4) includes: two sign inversion detection units (13a and 13b) that respectively detect sign inversions of an I signal (101) and a Q signal (102); a rotation judgment unit (14) that detects a direction in which a signal point rotates on an IQ plane; a counter unit (15) that counts an output of the rotation judgment unit (14); and an adjacent channel interference detection unit (16) that detects an imbalance in the number of times the signal point rotates in each direction, from the count in the counter unit (15). Adjacent channel interference is detected by an imbalance between the number of times the signal point rotates clockwise and the number of times the signal point rotates counterclockwise on the IQ plane.