Quadrature Error Correction in Direct Conversion Transmitters
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Solution Overview
Problem
Direct conversion wireless transmitters face challenges in achieving low undesired sideband levels due to quadrature errors, which can be exacerbated by digital pre-distortion and baseband filter mismatches, requiring effective calibration methods to correct these imbalances without disrupting ongoing operations.
Innovation Solution
A system and method that utilize a controller to identify and correct quadrature errors by generating a precoder matrix based on cross-covariance analysis and singular value decomposition, allowing for gain, phase, and group delay corrections through a parameterized linear transformation, enabling continuous operation and improved sideband suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If blind QEC algorithms are used to correct quadrature errors, then quadrature error correction is achieved, but DPD-related correlation is falsely detected as quadrature error, limiting minimum achievable undesired sideband
Solution Approach 1:
The patent segments the correlation detection process into two distinct parts: (1) detecting correlation between received signals to identify DPD usage, and (2) detecting correlation between I and Q TX signals to identify actual quadrature errors. This segmentation prevents false detection by analyzing different signal pairs separately, allowing accurate QEC even when DPD is present.
Solution Approach 2:
The patent performs preliminary detection of DPD-related correlation before executing the QEC process. By identifying the presence of DPD in advance through correlation analysis of received signals, the system can adjust its QEC strategy accordingly, preventing false detection from limiting the achievable sideband suppression.
2Measurement precision
If transmitter is placed offline for calibration to correct quadrature errors, then correction accuracy is improved, but dropped calls and other undesirable side effects occur
Solution Approach 1:
The patent enables continuous QEC calibration by performing the correction process online using live transmit signals. The system continuously monitors the transmit signal through a loopback path and adjusts correction parameters in real-time, maintaining system availability while achieving accurate quadrature error correction without taking the transmitter offline.
Solution Approach 2:
The patent implements self-calibration capability where the transmitter uses its own transmit signals to detect and correct its own quadrature errors. The system autonomously performs correlation analysis and adjusts correction parameters without requiring external calibration equipment or offline intervention, enabling continuous operation during self-correction.
3Device complexity
If direct conversion architecture is used to reduce system cost and size, then integration and component reduction are achieved, but quadrature errors result in undesired sideband emissions
Solution Approach 1:
The patent implements a feedback-based QEC system that continuously monitors the transmit signal for quadrature errors and adjusts correction parameters accordingly. The loopback receiver captures the transmit signal, the controller analyzes it for I/Q imbalance, and the correction parameters are fed back to the transmitter to compensate for quadrature errors, maintaining low sideband emissions in the integrated direct conversion architecture.
Solution Approach 2:
The patent dynamically adjusts correction parameters (gain ratios and phase shifts) to compensate for quadrature errors in the direct conversion architecture. By changing these parameters based on detected error levels, the system maintains accurate modulation and suppresses undesired sidebands while preserving the benefits of integration and component reduction.
Data Source
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AI summary
A transmission module is provided that includes a transmitter, a loopback receiver, and a QEC controller. The QEC controller identifies quadrature imbalance in the transmitter based at least one a comparison of the data signals at the output of the loopback receiver with data signals at the input of the transmitter. Based on the comparison, the QEC controller can adjust one or more characteristics of the transmitter to correct quadrature errors in the transmitter.