OFDM Receiver DC Offset Calibration With Symbol-Based Compensation
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Solution Overview
Problem
Existing methods for calibrating DC offset in OFDM systems face a tradeoff between signal distortion and interference leakage, as high-pass filters either introduce distortion or allow strong DC interference, making it challenging for system designers to achieve optimal performance.
Innovation Solution
A DC calibration circuit that includes an accumulator to estimate and subtract the DC offset from subsequent symbols, using timers and a compensator to apply the correction, with optional filter circuits for additional correction, reducing distortion and interference while minimizing time and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a high-pass filter with high corner frequency is used to remove DC offset quickly, then the calibration time is reduced, but signal distortion increases
Solution Approach 1:
The patent segments the DC offset removal process into two distinct stages: (1) a fast initial removal phase using a high-pass filter with higher corner frequency to quickly eliminate strong DC interference, and (2) a refinement phase using a low-pass filter to remove residual DC components while minimizing signal distortion. This segmentation allows each filter to operate in its optimal performance range.
Solution Approach 2:
The patent applies preliminary action by using the high-pass filter first to perform theç²— removal of DC offset before the low-pass filter performs fine removal. The high-pass filter prepares the signal by eliminating the dominant DC component, making the subsequent low-pass filtering more effective and less distortion-prone.
2Object-affected harmful factors
If a high-pass filter with low corner frequency is used to minimize signal distortion, then DC offset removal is more accurate, but calibration time increases and strong DC interference leakage occurs during initial symbols
Solution Approach 1:
The patent divides the filtering task into two segments: the high-pass filter handles the time-critical initial DC removal, while the low-pass filter handles the accuracy-critical residual DC removal. This segmentation allows the system to achieve both fast calibration and low distortion.
Solution Approach 2:
The high-pass filter acts as an intermediary that prepares the signal for the low-pass filter by removing the bulk of DC interference first. This intermediate step enables the low-pass filter to work more effectively with reduced burden, achieving better overall performance.
3Device complexity
If a single high-pass filter is used for DC offset calibration, then the device complexity is low, but the system cannot simultaneously achieve fast calibration and low distortion
Solution Approach 1:
The patent merges two complementary filtering approaches (high-pass and low-pass) into a unified DC offset calibration system. Each filter addresses different aspects of the problem, and their combined effect achieves superior calibration performance that neither filter could achieve alone.
Solution Approach 2:
The dual-filter system serves multiple functions: the high-pass filter provides fast initial DC removal, while the low-pass filter provides precise residual DC removal. This multi-functionality allows the system to achieve both speed and accuracy in DC offset calibration.
Data Source
AI summary
In accordance with the teachings described herein, systems and methods are provided for calibrating DC offset in a receiver. A DC calibration circuit may be used that is configured to receive a digital multi-carrier modulated (MCM) signal that includes a sequence of MCM symbols. The DC calibration circuit may include an accumulator and a compensator. The accumulator may be used to determine an estimated DC offset of a current MCM symbol in the sequence of MCM symbols. The compensator may be used to remove the estimated DC offset from a next MCM symbol in the sequence of MCM symbols. The accumulator may also be used to receive a plurality of digital samples that comprise the current MCM symbol and to determine the estimated DC offset by calculating an average of the plurality of digital samples.