Receiver Calibration via Frequency Conversion for I-Q Mismatch
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Solution Overview
Problem
In wireless receivers using zero-IF and low-IF systems, phase and amplitude mismatches between in-phase and quadrature components lead to bit error rate deterioration, especially in high-speed communication schemes like 16 QAM and 64 QAM, and existing calibration methods require long calibration times, making them unsuitable for rapid channel switching and image rejection.
Innovation Solution
A receiver configuration that includes mixers, signal paths for filtering and amplification, a calibration circuit for phase and amplitude mismatch, a frequency converter to elevate calibration signals to a higher frequency, and an arithmetic operation circuit to calculate and correct mismatches, allowing for reduced calibration time by performing calculations at a frequency higher than the IF frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If calibration is performed at IF frequency using conventional methods, then calibration accuracy is achieved, but calibration time becomes excessively long
Solution Approach 1:
The patent changes the frequency parameter of calibration signals from IF frequency to a higher frequency (such as RF frequency). This parameter change allows the calibration process to converge faster while maintaining accuracy, as the higher frequency signals provide better resolution for detecting phase and amplitude mismatches between I and Q components.
Solution Approach 2:
The patent performs preliminary calibration actions at a higher frequency before actual signal processing. By pre-calibrating the I-Q mismatch at a higher frequency where measurements are more sensitive, the system establishes accurate correction factors that can then be applied during normal operation, reducing the need for lengthy calibration procedures.
2Speed
If rapid channel switching is implemented, then system responsiveness is improved, but calibration accuracy deteriorates due to insufficient calibration time
Solution Approach 1:
By changing the calibration signal frequency to a higher value, the patent enables faster calibration convergence. This allows the system to perform accurate calibration in shorter time periods, making it feasible to implement rapid channel switching without sacrificing calibration quality.
3Object-affected harmful factors
If image rejection is performed in low-IF system, then image signal suppression is achieved, but phase and amplitude mismatch calibration becomes more difficult
Solution Approach 1:
The patent extracts the calibration function from the signal processing path by using dedicated calibration signals at higher frequencies. This separation allows image rejection to be performed independently in the low-IF path while calibration occurs at a higher frequency where I-Q mismatch effects are more pronounced and easier to measure, eliminating the interference between these two functions.
Data Source
AI summary
This invention provides a receiver in which the calibration time by repeated operations to correct phase mismatch and amplitude mismatch between I and Q signals can be reduced. The receiver comprises mixers which convert received RF signals into quadrature modulated IF signals, signal paths which filter and amplify and output the quadrature modulated signals output from the mixers, a calibration circuit which calibrates phase and amplitude mismatches between the I and Q components of the quadrature modulated signals output through the signal paths, a frequency converter which, when the mixers or the signal paths selected output calibration signals with IF frequency instead of the quadrature modulated signals, converts the calibration signals into those with a frequency higher than IF frequency, and an arithmetic operation circuit which calculates phase and amplitude mismatches from the calibration signals output by the frequency converter and outputs calculation results. The calibration circuit executes calibration, using the calculation results.