SAR ADC Amplifier Bandwidth Switching for Thermal Noise Suppression
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Solution Overview
Problem
Successive approximation register (SAR) analog-to-digital converters (ADCs) face challenges in reducing noise effects, particularly thermal noise, which can impact the accuracy of the output code and limit the resolution of the conversion process.
Innovation Solution
The implementation of an auto-zeroing (AZ) sample phase noise suppression (AZSPNS) mechanism in the SAR ADC, which selectively adjusts the electrical attributes of the amplifier during the sample and conversion phases. This includes reducing the bandwidth during the sample phase to filter out higher-frequency thermal noise and increasing the bandwidth during the conversion phase to enhance data conversion accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bandwidth is reduced during the sample phase to filter out higher-frequency thermal noise, then the noise effects are reduced, but the conversion speed is slowed down
Solution Approach 1:
The amplifier bandwidth is made dynamic by switching between different bandwidth modes depending on the operational phase. During the sample phase, a first bandwidth (narrower) is used to filter thermal noise, while during the conversion phase, a second bandwidth (wider) is used to maintain conversion speed. This is achieved through circuit elements that can adjust their electrical characteristics based on the operational phase.
Solution Approach 2:
The conversion process is divided into distinct phases (sample phase and conversion phase), with each phase having optimized electrical attributes. The sample phase focuses on noise filtering with reduced bandwidth, while the conversion phase focuses on speed with increased bandwidth. This segmentation allows each phase to be optimized independently for its specific function.
2Measurement precision
If the bandwidth is increased during the conversion phase to enhance data conversion accuracy, then the conversion accuracy is improved, but the high-frequency noise is amplified
Solution Approach 1:
During the sample phase, the amplifier operates with reduced bandwidth to pre-filter thermal noise before the conversion phase begins. This preliminary noise filtering action prevents high-frequency noise from being amplified in the subsequent conversion phase, allowing the wider bandwidth to be used safely for accurate conversion.
Solution Approach 2:
The amplifier bandwidth is periodically adjusted according to the operational phase. The circuit alternates between a narrow bandwidth mode during sampling and a wide bandwidth mode during conversion. This periodic adjustment ensures that noise filtering occurs at the appropriate time before conversion, and that conversion accuracy is maintained when needed.
Data Source
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AI summary
A successive approximation analog-to-digital (100) with an input (102) for receiving an input analog voltage, and an amplifier (202) with a first set of electrical attributes in a sample phase and a second set of electrical attributes, differing from the first set of electrical attributes, in a conversion phase.