Low-IF Receiver DC Offset Removal via Digital Tone Subtraction
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Solution Overview
Problem
Conventional low-IF receivers face challenges in effectively removing dynamic DC components, which degrade signal quality and reduce the dynamic range of analog-to-digital converters, due to computationally intensive phase and amplitude estimation methods and non-linear phase responses from high-pass filters, and existing solutions assume static DC conditions that may not hold in dynamic environments.
Innovation Solution
A method involving a digital receiver and baseband processor that converts residual DC components to a tone, allowing for coherent subtraction by averaging the DC level over a data packet and using a coherent tone to null the DC offset, thereby improving signal detection and reducing noise contributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high-order high-pass filters are used to remove DC components, then DC removal effectiveness is improved, but group delay increases and signal distortion occurs
Solution Approach 1:
The patent segments the DC removal process into two independent stages: first removing static DC with a simple high-pass filter, then removing dynamic DC through digital signal processing by estimating and subtracting the DC component. This segmentation allows each stage to use optimized techniques without the trade-offs of high-order filters.
Solution Approach 2:
The patent replaces the mechanical/high-order filter approach with a digital signal processing approach. Instead of using analog high-pass filters with sharp cutoffs that cause group delay, the system uses digital estimation and subtraction methods that achieve DC removal without the time delays and phase distortions of high-order filters.
2Object-affected harmful factors
If high-order high-pass filters are used to remove DC components, then DC removal effectiveness is improved, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent divides DC removal into static and dynamic components, applying appropriate techniques to each. The static DC is removed with a simple filter, while dynamic DC is removed through digital estimation that preserves signal integrity, avoiding the SNR degradation caused by high-order filters.
Solution Approach 2:
The patent substitutes high-order analog filters with digital signal processing techniques. The digital estimation and subtraction method removes DC components more selectively without the aggressive frequency cutoffs that cause signal distortion and SNR loss in high-order filters.
3Measurement precision
If computational estimation of phase and amplitude is performed to remove DC, then DC removal accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent implements a dynamic DC removal approach that adapts to changing DC conditions during signal reception. By continuously estimating and subtracting the DC component, the system maintains high accuracy in dynamic environments without requiring overly complex computational algorithms.
Solution Approach 2:
The patent changes the approach from complex phase and amplitude estimation to a simpler mean-based estimation method. By calculating the average of signal samples and subtracting this mean value, the system achieves effective DC removal with reduced computational complexity compared to full phase and amplitude estimation.
Data Source
AI summary
Methods, apparatus, and articles of manufacture are disclosed for removing an undesired component from a low intermediate frequency signal having an intermediate center frequency and an undesired component at a first frequency. One example method may include determining an amplitude of the undesired component; frequency shifting the low intermediate frequency signal from the intermediate center frequency to produce a zero intermediate frequency signal; filtering the zero intermediate frequency signal; generating a tone based on the amplitude of the undesired component; and subtracting the tone from the filtered zero intermediate frequency signal to remove the undesired component.