SAR ADC Threshold Control for Noise-Robust LSB Conversion
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Solution Overview
Problem
Conventional SAR ADCs face challenges in achieving an improved signal to quantization noise ratio (SQNR) due to comparator noise, which affects the determination of least significant bits (LSBs) and results in sub-optimal performance.
Innovation Solution
The proposed SAR ADC employs multiple comparisons and statistical analysis of noise properties to determine LSBs and fractional bits, using a controller to generate appropriate thresholds and record comparison results, thereby enhancing the SQNR and effective number of bits (ENOB).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional SAR ADC uses single comparison for LSB determination, then device complexity is low, but measurement precision deteriorates due to comparator noise
Solution Approach 1:
The patent segments the LSB determination process into multiple independent comparison operations instead of using a single comparison. Each comparison provides a bit of information about the LSB, and these results are combined through statistical analysis to overcome comparator noise. This segmentation allows the system to achieve higher precision by aggregating multiple noisy measurements.
Solution Approach 2:
The patent implements feedback by using the results of first comparisons (performed with first thresholds) to determine the thresholds for second comparisons. The controller adjusts subsequent comparison thresholds based on previous comparison outcomes, creating a feedback loop that refines the LSB determination process and improves measurement precision.
2Measurement precision
If multiple comparisons are performed for LSB determination, then measurement precision improves, but loss of time increases due to additional comparison operations
Solution Approach 1:
The patent performs preliminary comparisons (first comparisons with first thresholds) to gather information about the input signal before performing the final LSB determination comparisons (second comparisons with second thresholds). This preliminary action allows the system to narrow down the search range and make the subsequent LSB determination more efficient, reducing the overall time penalty of multiple comparisons.
Solution Approach 2:
The patent performs a sufficient number of comparisons to achieve the desired precision level, even if some comparisons may be redundant. By performing slightly more comparisons than the absolute minimum, the system ensures that statistical noise is adequately suppressed while keeping the time overhead manageable through efficient parallel processing where applicable.
Data Source
AI summary
A successive approximation register (SAR) analog-to-digital converter (ADC) includes a comparator, a threshold generator and a controller. The comparator receives an analog signal and the SAR ADC outputs an output codeword. The comparator performs a plurality of first comparisons and a plurality of second comparisons. The controller determines a plurality of most significant bits of the output codeword according to a plurality of first comparison results corresponding to the first comparisons. The first comparisons are performed by comparing the analog signal with a plurality of first thresholds. The controller determines a plurality of least significant bits of the output codeword according to a plurality of second comparison results corresponding to the second comparisons. The second comparisons are performed by comparing the analog signal with a second threshold. The controller controls the threshold generator to produce the plurality of first thresholds and the second threshold according to the first comparison results.