Oversampling A/D Converter RC Filter Layout for Low-Distortion Stability
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Solution Overview
Problem
Conventional continuous-time delta sigma A/D converters (CTDS-ADCs) face challenges in reducing signal distortion and improving operational stability due to nonlinearity of active elements and the need for additional anti-aliasing filters, which complicates circuit configuration and increases power consumption.
Innovation Solution
The proposed oversampling A/D converter configuration includes specific filter structures with resistive and capacitive elements, operational amplifiers, and D/A converters, where resistance and capacitance values are set to predetermined ratios to remove the input signal before the second filter, reducing signal distortion and using the third filter as an anti-aliasing filter, thereby improving operational stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If active elements are used to sum fed forward input signal and output of continuous-time filters, then the circuit can perform signal processing, but signal distortion is caused by nonlinearity of the active elements
Solution Approach 1:
The patent extracts and removes the harmful nonlinearity effect by using passive RC filters instead of active elements for signal summation. The passive filter configuration eliminates the source of distortion while preserving the necessary signal processing function through careful selection of resistance and capacitance values.
Solution Approach 2:
The patent replaces expensive and problematic active elements with simple, inexpensive passive RC components. These passive elements provide the necessary signal processing without introducing distortion, effectively substituting complex active circuitry with simpler passive alternatives.
2Reliability
If anti-aliasing filter is inserted at stage preceding quantizer, then anti-aliasing processing is enabled, but additional filter with same configuration is needed preceding continuous-time filters, complicating circuit configuration
Solution Approach 1:
The patent merges the anti-aliasing filter function into the existing RC filter structure. By configuring the RC elements with specific resistance and capacitance values, the same filter circuit performs both signal processing and anti-aliasing functions, eliminating the need for separate duplicate filter stages.
Solution Approach 2:
The RC filter circuit is designed to serve multiple functions simultaneously: it acts as both the signal processing filter and the anti-aliasing filter. This multi-functional design reduces circuit complexity while maintaining reliable anti-aliasing protection.
3Reliability
If filter with active elements is used for anti-aliasing, then anti-aliasing processing is achieved, but signal distortion is caused by active elements
Solution Approach 1:
The patent replaces active elements in the anti-aliasing filter with simple passive RC components. This substitution eliminates signal distortion while maintaining anti-aliasing functionality, using inexpensive and reliable passive elements instead of problematic active devices.
Solution Approach 2:
The patent extracts the harmful nonlinearity by removing active elements from the anti-aliasing filter circuit. The passive RC configuration provides the necessary frequency filtering without introducing distortion, effectively separating the anti-aliasing function from the distorting active elements.
4Stability of the object's composition
If feedback from quantizer output to quantizer input is implemented, then operational stability is improved, but input signal cannot be removed at stage preceding continuous-time filters
Solution Approach 1:
The patent segments the signal processing into distinct functional stages: the RC filter stage handles input signal removal through specific R and C value selection, while the feedback loop handles stability improvement. This segmentation allows each stage to perform its specific function without interfering with the other.
Solution Approach 2:
The RC filter performs preliminary signal processing by removing the input signal component before the feedback loop operates. This preliminary action ensures that when feedback is applied for stability, the input signal has already been eliminated, preventing interference.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces signal distortion by eliminating active element interference and enhances operational stability by ensuring the input signal is removed before the continuous-time filters, while maintaining a large gain for the anti-aliasing filter.
Implementation Method 1
a first filter including a first resistive element configured to receive the input signal at a first end, a first capacitive element coupled to a second end of the first resistive element
Implementation Method 2
a first capacitive element coupled to a second end of the first resistive element at a first end, and coupled to a common node at a second end
Implementation Method 3
an operational amplifier coupled to a second end of the second resistive element at an inverting input terminal, and coupled to the common node at a non-inverting input terminal
Implementation Method 4
a number n of D/A converters, and then fed back to the respective number n of integrators
Data Source
AI summary
An oversampling A/D converter includes a first filter including a first resistive element, a first capacitive element, a second resistive element, an operational amplifier, and a second capacitive element; a second filter receiving an output of the first filter; a third filter including a third resistive element, a third capacitive element, and a fourth resistive element; a quantizer receiving an output of the third filter and generating a digital signal; and a D/A converter converting the digital signal to an analog current signal. The D/A converter inputs the generated analog current signal to an inverting input terminal of the operational amplifier.