SAR ADC Auto-Zero Amplifier Switching for Noise-Resilient Conversion
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Solution Overview
Problem
Successive approximation register (SAR) analog-to-digital converters (ADCs) face challenges in noise immunity, particularly due to noise effects that can cause signal state changes greater than the least significant bit (LSB) resolution, leading to errors in output or limiting resolution, especially as they operate at higher speeds and with more output bits.
Innovation Solution
The implementation of an auto-zeroing (AZ) sample phase noise suppression (AZSPNS) aspect, which selectively adjusts the electrical attributes of the amplifier during the sample and conversion phases, reduces noise susceptibility by filtering out higher-frequency thermal noise during the sample phase and offsetting its effects during conversion, thereby improving signal-to-noise ratio (SNR).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the reference voltage is adjusted to converge toward the analog input voltage signal in successive comparisons, then the output accuracy is improved, but the smaller reference voltage change in later comparisons becomes more susceptible to noise errors
Solution Approach 1:
The patent applies preliminary action by performing auto-zeroing during the sample phase before the conversion phase begins. The amplifier offset and high-frequency noise are captured and stored on the auto-zero capacitor during sampling, so that when conversion occurs, these harmful effects have already been preliminarily addressed, reducing their impact on the smaller reference voltage changes in later comparisons
Solution Approach 2:
The patent extracts harmful high-frequency noise and amplifier offset from the signal path during the sample phase. By using the auto-zeroing mechanism to separate and store these unwanted components on the auto-zero capacitor, they are removed from the conversion process, preventing them from degrading the accuracy of subsequent comparisons
2Reliability
If the amplifier bandwidth is reduced to filter out high-frequency thermal noise during the sample phase, then the signal-to-noise ratio is improved, but the conversion speed may be limited
Solution Approach 1:
The patent segments the operation into distinct sample phase and conversion phase with different amplifier configurations. During the sample phase, the amplifier operates with reduced bandwidth to filter noise. During the conversion phase, the amplifier switches to a different configuration that enables faster operation. This temporal segmentation allows both noise filtering and high-speed conversion to be achieved in their respective phases
Solution Approach 2:
The patent implements dynamic adjustment of the amplifier electrical attributes by switching between different configurations based on the operational phase. The amplifier's bandwidth and other electrical characteristics are dynamically changed from a noise-filtering configuration during sampling to a high-speed configuration during conversion, allowing the system to optimize performance for each phase's specific requirements
3Reliability
If the amplifier electrical attributes are selectively adjusted during sample and conversion phases, then noise suppression is improved, but the device complexity increases
Solution Approach 1:
The patent makes the single amplifier multi-functional by enabling it to operate in different configurations during different phases. The same amplifier circuit performs both noise-filtering during sampling and high-speed conversion during the conversion phase, eliminating the need for separate amplifiers for each function. The auto-zero capacitor also serves dual purposes: storing offset information and filtering high-frequency noise
Solution Approach 2:
The patent merges the auto-zeroing function with the noise filtering function into a single integrated mechanism. The auto-zeroing process simultaneously captures amplifier offset and filters high-frequency thermal noise, combining what could be separate functions into one unified operation that reduces overall circuit complexity while maintaining effective noise suppression
Data Source
AI summary
A successive approximation analog-to-digital with an input for receiving an input analog voltage, and an amplifier 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.