Orthogonal Modulator Calibration for I/Q Mismatch Compensation
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Solution Overview
Problem
Existing signal processing circuits for orthogonal modulators face challenges in accurately compensating for I/Q mismatches and DC offsets due to circuit limitations and high process voltage requirements, leading to reduced modulation accuracy and increased complexity.
Innovation Solution
A signal processing circuit that generates test signals represented by four points in point symmetry within the I/Q orthogonal coordinate system, allowing for the calculation of average envelope amplitudes to adjust and compensate for I/Q amplitude and phase mismatches, thereby reducing the effect of remaining DC offsets without requiring complex hardware or sine-wave generators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional compensation methods for DC offset and I/Q mismatch are implemented, then modulation accuracy is improved, but device complexity increases due to additional hardware components
Solution Approach 1:
The system uses its own output signal to perform self-diagnosis and self-compensation. The microcontroller analyzes the modulated signal and automatically adjusts compensation parameters without requiring external test equipment or additional dedicated compensation hardware, making the system self-sufficient and reducing overall complexity
Solution Approach 2:
The microcontroller serves multiple functions: it controls the I/Q modulator, processes the output signal, performs FFT analysis, calculates compensation parameters, and adjusts the compensation register. This multi-functional approach eliminates the need for separate dedicated compensation circuits and test signal generators
2Measurement precision
If sine-wave test signals are used for compensation, then I/Q mismatch compensation accuracy is improved, but device complexity increases due to the need for sine-wave generators and memory storage
Solution Approach 1:
The system eliminates the need for external sine-wave test signal generators by using the modulator's own output signal as the test signal. The microcontroller directly analyzes the modulated signal and extracts I/Q mismatch information without requiring separate test equipment
Solution Approach 2:
The invention extracts the necessary compensation information directly from the modulated output signal using FFT analysis. By taking out only the essential frequency components through spectral analysis, the system avoids the complexity of generating and storing complete sine-wave test signals while still achieving accurate I/Q mismatch measurement
3Manufacturing precision
If DC offset compensation is performed before I/Q mismatch compensation, then compensation effectiveness is improved, but the remaining DC offset affects measurement accuracy
Solution Approach 1:
The system implements a feedback mechanism where the microcontroller continuously monitors the modulated signal, analyzes I/Q mismatch using FFT, calculates compensation parameters, and adjusts the compensation register. This closed-loop feedback ensures that compensation is optimized based on actual signal characteristics rather than being affected by residual DC offsets
Solution Approach 2:
The system performs preliminary FFT analysis on the modulated signal to identify and separate the DC offset component from the I/Q mismatch characteristics. By analyzing the spectral components and using the relationship between I and Q channel spectra, the system can calculate I/Q mismatch parameters that are independent of the DC offset level
Data Source
AI summary
Test signal generator (3) generates test signals represented, by four points, which comprise two sets of two points positioned in point symmetry with respect to the origin of an I/Q orthogonal coordinate system. Envelope detector (8) detects the amplitude of an envelope of the output signal from an orthogonal modulator when the test signals represented by four points are generated, and outputs a signal proportional to the square of the amplitude. Comparing unit (9) calculates an average value of output signals from envelope detector ( ) when the test signals represented by the two points of each set are generated. Controller (10) adjusts the amplitudes and/or phases of the test signals so that the average values produced when the test signals represented by the two sets of the two points are generated are equal to each other, and calculates an I/Q mismatch quantity based on the adjusted results.