Transformed Interpolation-Decimation Filter for Spectral Image Suppression
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Solution Overview
Problem
Radio frequency (RF) sampling transceivers face challenges with high digital complexity and power consumption due to the need for significant digital up-conversion and down-conversion processes, which also occupy large digital areas and increase costs.
Innovation Solution
A low-power digital filter is introduced that reduces digital area and power consumption by applying transformations to filter coefficients to create symmetric and anti-symmetric sub-filters, which suppress undesired spectral images through a first transformation in the filter block and a second transformation in the input or output streams for interpolation and decimation processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital up-conversion and down-conversion processes are performed at high sampling rates (e.g., 9 GSPS), then RF signal processing capability is improved, but digital complexity and power consumption increase significantly
Solution Approach 1:
The filter is divided into multiple sub-filters that process different portions of the input signal. Each sub-filter operates at a lower effective sampling rate, reducing the digital complexity and power consumption of individual filter stages while maintaining the overall high sampling rate capability through parallel processing.
Solution Approach 2:
The patent introduces symmetry and anti-symmetry properties into the sub-filter coefficient sets. By designing sub-filters with these mathematical properties, the number of unique coefficients is reduced, allowing for more efficient hardware implementation with fewer multipliers and adders, thus reducing digital complexity while maintaining processing capability.
2Measurement precision
If high-speed ADC/DAC converters are used for direct RF sampling, then conversion performance is improved, but cost and power consumption increase
Solution Approach 1:
The patent employs dynamic filtering techniques where the filter structure adapts to the specific signal processing requirements. By using symmetry and anti-symmetry properties, the filter can dynamically adjust its computational requirements based on the input signal characteristics, maintaining high conversion performance while reducing power consumption through optimized computational paths.
3Reliability
If interpolation filters with many coefficients are used to suppress out-of-band images, then spectral image suppression is improved, but digital area and multiplication operations increase
Solution Approach 1:
The patent applies symmetry and anti-symmetry properties to the interpolation filter coefficients. This mathematical structure allows the filter to achieve the same spectral image suppression performance with fewer unique coefficients. The symmetric and anti-symmetric sub-filters can share common computational resources, significantly reducing the digital area required for implementation while maintaining effective out-of-band image suppression.
4Measurement precision
If decimation filters with many coefficients are used for down-conversion, then down-conversion accuracy is improved, but addition operations and digital complexity increase
Solution Approach 1:
The decimation filter is segmented into multiple sub-filters with symmetry and anti-symmetry properties. This segmentation allows the filter to process the down-conversion task in parallel stages, reducing the computational burden on any single stage. The structured coefficient sets enable efficient implementation with reduced addition operations while maintaining down-conversion accuracy.
Data Source
AI summary
A digital filter for interpolation or decimation and a device incorporating the digital filter is disclosed. The digital filter includes a filter block, a first transformation circuit coupled to the filter block and an input stream coupled to provide input values to a component selected from the filter block and the first transformation circuit. The filter block includes a pair of sub-filters having respective transformed coefficients, the respective transformed coefficients of a first sub-filter of the pair of sub-filters being symmetric and the respective transformed coefficients of a second sub-filter of the pair of sub-filters being anti-symmetric. The first transformation circuit is coupled to perform a first transformation; the filter block and the first transformation circuit together provide suppression of undesired spectral images in final outputs of the digital filter.