I/Q Mixer Gain Calibration for Higher Image Rejection
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Solution Overview
Problem
The direct conversion method in radio-signal receivers faces reduced image response rejection ratio (IMRR) due to shifted amplitudes of I and Q signals, which affects interference suppression.
Innovation Solution
A reception apparatus with in-phase and quadrature-side mixers, error detection signal generation, and signal processing units that utilize four-phase detection signals to equalize I and Q signal amplitudes, adjusting gains through filter circuits and current-to-voltage conversion units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If quadrature demodulation is performed using local signals in a direct conversion method, then image frequency signal suppression is improved, but amplitude shifts between I and Q signals occur reducing IMRR
Solution Approach 1:
The patent applies preliminary action by performing amplitude error detection and gain adjustment using four-phase detection signals before actual signal reception. The system pre-calibrates the I and Q signal amplitudes by detecting errors with multiple phase signals and adjusting gain in advance, ensuring amplitude equality is established before normal operation begins.
Solution Approach 2:
The patent implements feedback by continuously monitoring amplitude errors between I and Q signals using the four-phase detection signal method and automatically adjusting the gain of the local signals. The system detects amplitude discrepancies and feeds this information back to the gain control mechanism, creating a closed-loop system that maintains amplitude equality dynamically.
2Manufacturing precision
If gain adjustment is performed to equalize I and Q signal amplitudes, then image response rejection ratio is improved, but detection accuracy of amplitude errors must be maintained
Solution Approach 1:
The patent applies dimensionality change by introducing four-phase detection signals (0°, 45°, 90°, 135°) instead of conventional single-phase detection. This multi-dimensional approach provides multiple measurement perspectives for amplitude error detection, enabling more accurate and comprehensive error detection across different phase conditions, thereby maintaining detection accuracy while enabling precise gain adjustment.
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
Enhances image response rejection ratio (IMRR) by correcting amplitude differences between I and Q signals, improving interference rejection characteristics.
Implementation Method 1
an in-phase-side mixer that mixes a predetermined high-frequency component and an in-phase-side local signal, and outputs the mixed signal as an in-phase-side mixed signal
Implementation Method 2
a quadrature-side mixer that mixes the predetermined high-frequency component and a quadrature-side local signal orthogonal to the in-phase-side local signal, and outputs the mixed signal as a quadrature-side mixed signal
Data Source
AI summary
Provided is a reception apparatus that includes an in-phase-side mixer that mixes a high-frequency component and an in-phase-side local signal, and outputs the mixed signal as an in-phase-side mixed signal, a quadrature-side mixer that mixes the high-frequency component and a quadrature-side local signal orthogonal to the in-phase-side local signal, and outputs the mixed signal as a quadrature-side mixed signal, an error detection signal generation unit that generates four-phase detection signals having same frequencies as frequencies of the in-phase-side local signal and quadrature-side local signal, and each having a different phase, and a signal processing unit that generates a gain difference between an in-phase-side signal according to the in-phase-side mixed signal and a quadrature-side signal according to the quadrature-side mixed signal, on the basis of respective output signals of the in-phase-side mixer and quadrature-side mixer in a case where each of the four-phase detection signals is the high-frequency component.