RF Transmitter Phase Alignment via DC Offset Calibration
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Solution Overview
Problem
Current radio frequency (RF) communication systems face challenges in phase alignment among multiple transmitters, which is crucial for successful beamforming and reducing multipath fading, but existing methods are complex and prone to errors due to DC offset and I/Q imbalance.
Innovation Solution
The method involves creating a loop between an RF transmitter and receiver, measuring DC signals with and without a non-zero DC insertion, and calculating relative phase differences using on-chip calibration and Quadrature Modulator Correction to simplify phase alignment and reduce complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex controllers are used to control transmission and receiving elements in MIMO systems, then phase alignment and beamforming can be achieved, but device complexity increases
Solution Approach 1:
The system performs self-calibration by automatically measuring DC offsets and I/Q imbalances at the receiver and computing correction values without external intervention. The baseband processor autonomously adjusts transmitter phases by applying calculated correction values, enabling the system to self-correct phase alignment issues without complex external control equipment.
Solution Approach 2:
The patent changes the measurement parameter from complex modulated signals to simple DC signals for phase offset measurement. By measuring DC offsets at the receiver output and using these measurements to calculate phase correction values, the system simplifies the measurement process while maintaining phase alignment accuracy, avoiding the need for complex test signal sequences.
2Device complexity
If DC offset and I/Q imbalance are present in the RF chain, then measurement accuracy deteriorates, but simpler measurement methods become feasible
Solution Approach 1:
The system performs preliminary calibration by measuring DC offsets and I/Q imbalances before actual phase alignment measurements. The baseband processor calculates correction values for DC offsets and I/Q imbalances in advance, then applies these corrections to subsequent measurements, ensuring accurate phase offset measurement despite the presence of these impairments.
Solution Approach 2:
The patent converts the harmful effects of DC offset and I/Q imbalance into useful calibration information. By deliberately measuring the DC components affected by these impairments and calculating correction values from them, the system transforms the previously harmful effects into the basis for accurate phase alignment correction.
3Device complexity
If phase alignment is performed without calibration, then device complexity is reduced, but measurement precision deteriorates due to DC offset and I/Q imbalance
Solution Approach 1:
The calibration process is segmented into distinct steps: DC offset measurement, I/Q imbalance measurement, correction value calculation, and application. The baseband processor separately measures I and Q channel DC components, calculates individual correction values for each channel, then applies them systematically, making the calibration process manageable and accurate without overwhelming complexity.
Data Source
AI summary
Systems and methods for phase alignment among multiple transmitters are described. In some embodiments, a method may include creating a loop between an RF transmitter and an RF receiver; measuring a first DC signal on the I and Q paths of the RF receiver without inserting a DC signal in the I and Q paths of the RF transmitter; measuring a second DC signal on the I and Q paths of the RF receiver while inserting a non-zero DC signal in the I and Q paths of the RF transmitter; and calculating a relative phase difference between the RF transmitter and the RF receiver using the first and second DC signals.