Delta-Sigma ADC Feedback Filtering for Adjacent Channel Suppression
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Solution Overview
Problem
Radio receivers face challenges in efficiently converting radio frequency signals to digital form due to the need for higher dynamic range in analog-to-digital converters (ADCs) to handle strong adjacent channel signals, leading to increased complexity, size, and power consumption.
Innovation Solution
A delta-sigma ADC with a feedback structure that filters channel selection, using multiple branches with digital-to-analog converters and feedback filters to attenuate undesired frequencies, allowing more dynamic range to be utilized by the desired signal, thereby reducing the ADC's dynamic range requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the dynamic range of the ADC is increased to handle strong adjacent channel signals, then the ADC can process both desired and undesired signals, but the complexity, size and power consumption of the ADC increase
Solution Approach 1:
The feedback path is segmented into multiple parallel branches, each with its own digital-to-analog converter and feedback filter. The first branch processes frequencies desired to be enhanced while the second branch processes frequencies not desired to be enhanced, allowing selective attenuation of adjacent channel signals without increasing overall ADC dynamic range requirements
Solution Approach 2:
Different feedback filters are applied to different frequency components through the multiple branches. The first feedback filter has a gain-to-frequency characteristic that attenuates frequencies desired to be enhanced, while the second feedback filter handles other frequencies differently, enabling frequency-selective processing that reduces the dynamic range burden on the ADC
2Device complexity
If channel-select filters are used to suppress adjacent channel signals, then the ADC dynamic range requirements are reduced, but the filters have limited adjacent channel suppression capability
Solution Approach 1:
A feedback loop is implemented where the digital representation from the quantizer is fed back through multiple branches with digital-to-analog converters and feedback filters. The feedback signal is subtracted from the input signal in a subtraction element, creating a closed-loop system that enhances adjacent channel suppression through the frequency-selective characteristics of the feedback filters
Solution Approach 2:
The channel-select filtering function is merged with the feedback mechanism of the delta-sigma ADC. Multiple feedback branches are combined in a subtraction element, integrating the filtering operation into the core conversion process rather than using separate external filters, thereby improving adjacent channel suppression while maintaining ADC efficiency
Data Source
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AI summary
A delta-sigma analog-to-digital converter (ADC) is disclosed. The ADC comprises a forward path structure; a feedback structure; and a first subtraction element arranged to receive an input signal to the delta-sigma analog-to-digital converter and a feedback signal from the feedback structure and output a difference signal, which is a difference between the input signal and the feedback signal, to the forward path structure, wherein the forward path structure comprises a quantizer arranged to convert an analog input signal to a digital representation; a forward path filter arranged to input the difference signal and provide an output signal to the quantizer, and the feedback structure comprises a first and a second branch, wherein the first branch comprises a first digital-to-analog converter arranged to provide output signals to the subtraction element; and a first feedback filter having a gain to frequency characteristic such that frequencies that are desired in the analog-to-digital conversion, compared to undesired frequencies, are attenuated in the feedback structure, and the second branch comprises a second digital-to-analog converter, wherein the first and second branches are fed by the digital representation and the outputs of the first and second branches are merged in a second subtraction element arranged to output a signal, which is a difference between the signals from the first and second branches, to the first subtraction element. A radio receiver, communication apparatus, method for analog-to-digital conversion, and computer program for implementing the method are also disclosed.