DC Offset Cancellation in Low-IF WLAN Transceivers
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Solution Overview
Problem
Conventional low-IF WLAN transceivers suffer from DC offsets due to mismatched complex operators, leading to spurious emissions, reduced amplification efficiency, and deteriorated transmission quality, particularly in broadband systems where carrier and LO bands overlap.
Innovation Solution
A method involving the use of correction signals to compensate for DC offsets by determining the optimum value through indicator signals, utilizing feedback loops and compensator units to minimize DC offsets in both I and Q signals, thereby preventing LO feedthrough and enhancing amplification efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex filters are used to suppress image frequency signals in low-IF WLAN transceivers, then image rejection is improved, but DC offsets are generated due to mismatched complex operators
Solution Approach 1:
The patent measures the DC offset caused by complex filter mismatch and uses this information to generate correction signals that cancel the harmful DC offset. The harmful effect (DC offset) is converted into useful information for calibration, allowing the system to compensate for component mismatches and eliminate spurious emissions at the LO frequency
Solution Approach 2:
The patent implements a feedback mechanism where the DC offset level is continuously measured and used to adjust correction signals. The system measures the DC offset component in the transmitted signal, generates appropriate correction signals based on the measurement, and applies these corrections to minimize the DC offset, creating a closed-loop control system that adapts to component variations
2Device complexity
If DC offsets are not compensated, then device complexity is reduced, but spurious emissions increase and transmission quality deteriorates
Solution Approach 1:
The patent implements a self-calibration mechanism where the transceiver automatically measures its own DC offset and generates correction signals without requiring external calibration equipment. The system uses its own transmitted signal to measure the DC offset component and adjusts its operation to compensate for mismatches, enabling the device to self-correct its performance issues
Solution Approach 2:
The patent changes the DC offset parameter by generating correction signals that adjust the offset level. The system measures the actual DC offset present in the signal path and dynamically adjusts correction parameters to minimize the offset, allowing the system to adapt to manufacturing variations and environmental changes without redesigning the hardware
3Loss of energy
If correction signals are applied to minimize DC offsets, then amplification efficiency is improved, but device complexity increases due to additional compensator units and feedback loops
Solution Approach 1:
The patent combines the DC offset measurement and correction functionality with the existing signal processing paths in the low-IF transceiver. The correction signals are integrated into the existing I and Q signal paths, and the measurement process utilizes the existing transmitted signal rather than requiring separate measurement circuits, thereby reducing the overall complexity increase
Data Source
AI summary
A method of transmitting information in a WLAN (Wireless Local Area Network) network and corresponding WLAN communication devices and integrated circuit chips are provided. A correction signal is used for compensating for a dc offset in a data signal containing at least part of the information to be transmitted. The correction signal is varied by making it taking different values. For each of the different values, a strength of an indicator signal indicative of the dc offset is determined. Based upon the determined strength, an optimum value of the correction signal is identified at which the dc offset is minimized. The value of the correction signal is set to the optimum value. Further, a method of transmitting information in a WLAN network is provided, including compensating for a first and second dc offset in a first and second data signal, respectively, using a first and second feedback loop, respectively.