Polyphase Digital Down Converter for Low-Power Spur Filtering
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Solution Overview
Problem
Existing digital down converter (DDC) circuits face challenges in efficiently down converting RF signals to baseband while minimizing sampling rate and addressing cross-talk spurious signals, particularly in high-frequency applications like satellite receivers, where power consumption and complexity are concerns.
Innovation Solution
A digital down converter comprising a commutator structure for polyphase filtering, complex band pass polyphase filters, and a baseband notch filter to generate in-phase and quadrature components at baseband, reducing the need for complex rotators and simplifying spur filtering, with shared latch elements and efficient decimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high sampling rate is used in the ADC to process RF signals at high center frequencies, then the signal processing accuracy is improved, but the power consumption and device complexity increase significantly
Solution Approach 1:
The patent segments the signal processing into two distinct stages: first, a lower-rate ADC samples the RF signal, and then a digital up-converter reconstructs the high-frequency signal in the digital domain. This segmentation allows the power-intensive high-frequency processing to occur digitally rather than requiring a high-rate ADC, thereby reducing power consumption while maintaining signal processing accuracy.
Solution Approach 2:
The patent introduces a digital up-converter as an intermediary component between the low-rate ADC and the signal processing chain. This intermediary reconstructs the high-frequency signal digitally, eliminating the need for a high-rate ADC and reducing power consumption while preserving the ability to process high-center-frequency signals with high accuracy.
2Measurement precision
If a high sampling rate is used in the ADC, then the signal processing accuracy is improved, but the device complexity increases
Solution Approach 1:
The patent segments the signal processing into two distinct stages: first, a lower-rate ADC samples the RF signal, and then a digital up-converter reconstructs the high-frequency signal in the digital domain. This segmentation allows the signal processing accuracy to be maintained through digital processing while the ADC complexity is reduced by operating at a lower sampling rate.
Solution Approach 2:
The patent introduces a digital up-converter as an intermediary component between the low-rate ADC and the signal processing chain. This intermediary reconstructs the high-frequency signal digitally, eliminating the need for a complex high-rate ADC while preserving signal processing accuracy through subsequent digital filtering and processing.
3Reliability
If conventional filtering methods are used to remove spurious signals, then the signal purity is improved, but the device complexity and power consumption increase
Solution Approach 1:
The patent applies preliminary digital filtering after the digital up-conversion to remove spurious signals and imaging artifacts before further signal processing. By performing this filtering in the digital domain at a lower effective sampling rate, the patent achieves high signal purity while avoiding the complexity of high-frequency analog or digital filters that would be required if filtering were performed earlier in the chain.
Data Source
AI summary
A digital down converter is disclosed. The digital down converter includes an input for receiving a sampled signal having a frequency band of interest, sampled at a first sampling rate, a commutator structure for distributing a set of real sampled signals for polyphase filtering, a complex band pass polyphase filter associated with the distributed signals, for generating in phase and quadrature filtered components, a baseband notch filter, and a frequency translator for generating in phase and quadrature components of the frequency band of interest at baseband.