I/Q Imbalance Compensation Using Phase-Shifted LO Feedback
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Solution Overview
Problem
Direct upconversion and downconversion systems in wireless communication devices often suffer from in-phase (I) and quadrature-phase (Q) imbalance due to a single local oscillator (LO) implementation, leading to distortion that is difficult to correct, especially with temperature and semiconductor aging effects.
Innovation Solution
A communication system that uses phase-shift control components and digital predistortion circuits to monitor and adjust signal characteristics, employing two LO signals phase-shifted relative to each other to generate and demodulate signals, allowing for adaptive correction of I and Q imbalances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single local oscillator (LO) is employed for both upconversion and downconversion, then design simplicity is improved and cost/size are reduced, but in-phase and quadrature-phase imbalance distortion occurs
Solution Approach 1:
The system employs a feedback mechanism where the receive-path signal is monitored and compared against expected characteristics. The predistortion circuit uses this feedback information to automatically adjust and correct I-Q imbalance in real-time, resolving the distortion caused by single LO implementation while maintaining design simplicity.
Solution Approach 2:
The invention dynamically changes system parameters by using phase-shift control components to adjust the phase relationship between LO signals during different time durations. This allows the system to adaptively correct I-Q imbalance by modifying signal characteristics rather than requiring complex hardware changes.
2Manufacturing precision
If manual calibration is used to correct I-Q imbalance, then signal balance can be improved, but the calibration is insufficient for long-term correction due to temperature and semiconductor aging effects
Solution Approach 1:
The system transitions from static manual calibration to dynamic automatic correction. The predistortion circuit continuously monitors receive-path signal characteristics and adjusts I-Q balance in real-time, allowing the system to adapt to changing conditions caused by temperature variations and semiconductor aging, thereby ensuring long-term reliability.
Solution Approach 2:
The system performs self-correction through the predistortion circuit that automatically detects and compensates for I-Q imbalance without requiring external manual intervention. This self-service capability ensures continuous adaptation to environmental changes and component aging.
3Reliability
If phase-shift control components and predistortion circuits are implemented, then long-term signal balance and quality are improved, but device complexity increases
Solution Approach 1:
The predistortion circuit applies preliminary correction to the transmit-path signal before it causes distortion. By pre-compensating for anticipated I-Q imbalance and nonlinearities, the system reduces the need for complex post-processing and simplifies the overall correction architecture while maintaining high signal quality.
Data Source
AI summary
In one embodiment of the invention, a modulator mixes a transmit-path signal based on a local oscillator (LO) signal and an amplifier amplifies the mixed transmit-path signal to generate an output signal for transmission. A demodulator generates a receive-path signal based on the output signal and the LO signal. Phase-shift control components provide the output signal and the LO signal to the demodulator during a first time duration and provide a phase-shifted version of one of the output signal and the LO signal to the demodulator during a second time duration. The demodulator generates a second receive-path signal based on the one of the phase-shifted output signal and the phase-shifted LO signal during the second time duration. At least one predistortion circuit adjusts at least one of the transmit-path signal and the receive-path signal based on a difference in signal characteristics of the receive-path signal during the second time duration relative to the first time duration.