Delta-Sigma ADC Feedback Filtering for Adjacent Channel Suppression
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Solution Overview
Problem
Radio frequency (RF) analog-to-digital converters in radio receivers face challenges in efficiently utilizing their dynamic range due to the presence of strong adjacent channel signals, leading to increased complexity, size, and power consumption, as existing filters have limited adjacent channel suppression.
Innovation Solution
A delta-sigma analog-to-digital converter is employed with a feedback structure that includes multiple branches with digital-to-analog converters and filters, attenuating undesired frequencies, allowing for dynamic range optimization by providing feedback for channel selection, thereby enhancing the converter's performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If channel-select filters are used to suppress adjacent channel signals, then adjacent channel suppression is improved, but device complexity increases
Solution Approach 1:
The patent combines the channel-select filter function with the ADC feedback structure by placing a filter in the feedback path from the quantizer output back to the summing junction. This merging eliminates the need for separate CSF components while achieving adjacent channel suppression through the feedback mechanism.
Solution Approach 2:
The feedback filter serves multiple functions simultaneously: it provides adjacent channel suppression, shapes the noise transfer function, and maintains loop stability. This multi-functionality reduces overall system complexity by consolidating what would otherwise require separate components.
2Measurement precision
If ADC dynamic range is increased to accommodate strong adjacent channel signals, then signal integrity is improved, but power consumption increases
Solution Approach 1:
The patent uses feedback from the quantizer output through a filter back to the summing junction to suppress adjacent channel signals. This feedback mechanism allows the ADC to maintain lower dynamic range requirements because the feedback path actively cancels out strong adjacent channel components, reducing the burden on the ADC's inherent dynamic range.
Solution Approach 2:
The feedback filter's gain-to-frequency characteristic is designed to attenuate frequencies that are undesired (adjacent channels) while preserving desired signal frequencies. By changing the frequency-dependent gain parameters of the feedback path, the system optimizes signal integrity without requiring increased overall ADC dynamic range.
3Object-affected harmful factors
If feedback filter is added to provide channel selection, then adjacent channel suppression is improved, but device complexity increases
Solution Approach 1:
The feedback filter is integrated into the existing ADC feedback structure, merging the channel-select functionality with the quantizer feedback path. This eliminates the need for separate CSF components and reduces overall device complexity while achieving adjacent channel suppression.
Solution Approach 2:
The feedback filter uses the quantizer output signal itself to generate the feedback that suppresses adjacent channels. The system serves itself by using its own output to cancel unwanted components at the input, eliminating the need for external filtering components.
Data Source
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.