Continuous-Time Sigma-Delta ADC Feedback Filtering for Low-Power Op-Amps
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Solution Overview
Problem
Conventional continuous time sigma-delta analog-to-digital converters require operational amplifiers with high bandwidth and high slew rate to suppress distortion and maintain a high signal-to-noise ratio, leading to high power dissipation and performance demands.
Innovation Solution
The design incorporates a feed-forward integrator path with a feedback digital-to-analog converter and a low pass filter, which reduces the bandwidth and slew rate requirements of the operational amplifier by suppressing high-frequency components before they reach the amplifier, using a feedback resistor and capacitor configuration to achieve loop stability and noise transfer functions comparable to prior art solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If operational amplifiers with high bandwidth and high slew rate are used, then distortion is suppressed and signal-to-noise ratio is maintained, but power dissipation increases
Solution Approach 1:
The patent segments the integrator function into two separate paths: a feed-forward path that handles the main integration function, and a feedback path that handles error correction and stability. This segmentation allows the operational amplifier to operate with relaxed bandwidth and slew rate requirements while maintaining overall system performance through coordinated operation of both paths.
Solution Approach 2:
The patent introduces a feedback low-pass filter as an intermediary component between the feedback digital-to-analog converter and the summator. This filter mediates the feedback signal by suppressing high-frequency components before they reach the operational amplifier, thereby reducing the amplifier's burden and power consumption while maintaining signal integrity.
2Reliability
If operational amplifiers with high bandwidth are used, then feedback signal distortion is suppressed, but device complexity and performance demands increase
Solution Approach 1:
The patent applies preliminary action by suppressing high-frequency components in the feedback path before they can cause distortion in the operational amplifier. The feedback low-pass filter performs this preliminary filtering, preventing problematic frequency components from reaching the amplifier and thus reducing its bandwidth requirements.
Solution Approach 2:
The patent extracts the high-frequency suppression function from the operational amplifier and places it in a dedicated feedback low-pass filter. This extraction allows the operational amplifier to focus on its primary integration function with relaxed bandwidth requirements, while the filter handles the high-frequency component removal.
3Object-generated harmful factors
If low pass filter is added to feedback path, then high-frequency noise is suppressed, but device complexity increases
Solution Approach 1:
The feedback low-pass filter serves multiple functions simultaneously: it suppresses high-frequency noise, stabilizes the feedback signal, and reduces the bandwidth requirements of the operational amplifier. This multi-functionality justifies the added component by providing multiple benefits from a single element.
Solution Approach 2:
The patent implements feedback by routing the filtered analog signal back to the summator through the feedback low-pass filter. This feedback mechanism continuously corrects errors and maintains system stability, with the filter ensuring that only appropriate frequency components are fed back, thereby suppressing high-frequency noise effectively.
Data Source
AI summary
A continuous time sigma-delta analog-to-digital converter comprising: a summator of an input analog signal and a feedback signal; a feed-forward integrator path connected to the summator and configured to provide a digital signal; a feedback digital-to-analog converter to convert the digital signal into a feedback analog signal; a feedback low pass filter structured to filter the feedback analog signal and provide the feedback signal to the summator.