Baseband Equalization in Digital Down-Converters for ADC Misalignment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-speed analog-to-digital converters (ADCs) in wireless receivers face challenges in correcting misalignment of frequency responses between sub-ADCs, leading to signal distortions, and existing solutions either do not fully exploit the potential for reducing the number of multipliers or are not applicable in real-time down-conversion applications.
Innovation Solution
The proposed digital down-converter design includes a configuration where frequency transformation is performed in parallel for each partial digital signal, using IQ demodulators and misalignment equalizers to correct frequency responses, allowing for a reduced number of multipliers and enabling real-time operation by calculating the frequency responses of misalignment equalizers to eliminate spurious components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional FIR filters are used for equalization in digital down-converters, then frequency response misalignment can be corrected, but the number of multipliers increases significantly making real-time operation difficult
Solution Approach 1:
The equalization process is segmented into two separate stages: misalignment equalization (correcting frequency response differences between sub-ADCs) and full-bandwidth equalization (correcting remaining distortions). This segmentation allows the misalignment equalizer to operate with fewer taps since it only needs to correct specific misalignment issues, not the entire frequency spectrum, thereby reducing the number of multipliers required while still achieving effective equalization.
Solution Approach 2:
The misalignment equalizer performs preliminary correction of frequency response misalignment between sub-ADCs before the signal proceeds to the full-bandwidth equalizer. By addressing the misalignment issue first with a reduced-complexity equalizer, the subsequent full-bandwidth equalization requires fewer resources, enabling real-time operation in FPGA implementations.
2Device complexity
If the equalizer bandwidth is reduced to match the processed signal bandwidth, then the number of multipliers is reduced, but the equalizer cannot correct misalignment when placed after low pass filters
Solution Approach 1:
The equalization function is segmented into two distinct components: a misalignment equalizer that corrects frequency response differences between sub-ADCs, and a full-bandwidth equalizer that handles remaining distortions. This segmentation allows the misalignment equalizer to be positioned after the low pass filter with reduced bandwidth, reducing the number of multipliers, while still maintaining misalignment correction capability through the dedicated misalignment equalization stage.
Solution Approach 2:
The misalignment equalizer is designed with local quality optimized for correcting specific misalignment issues in the baseband signal, rather than attempting full-bandwidth equalization. This localized approach allows the equalizer to operate effectively with fewer taps and multipliers when placed after the low pass filter, while the full-bandwidth equalizer handles the remaining frequency-dependent distortions.
3Adaptability or versatility
If adaptive equalization is used for frequency response correction, then flexibility is improved, but time lag and convergence issues prevent real-time application
Solution Approach 1:
The misalignment equalizer coefficients are calculated in advance based on the known frequency response characteristics of the sub-ADCs, rather than adapting in real-time. This preliminary calculation of equalization parameters eliminates convergence time and allows the equalizer to operate at full real-time speed, while still providing flexible correction for frequency response misalignment.
Data Source
AI summary
A digital down-converter with baseband equalization comprises a composite analog-to-digital converter (ADC) adapted to convert an applied RF analog signal to be processed to a digital signal, and then down-convert the digital signal to a baseband frequency region, and then perform equalization on the down-converted digital signal, thereby reducing distortions caused by introduction of spurious signals by the ADC.