ADC Correction Circuit for Settling Error in MSB Conversion
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Solution Overview
Problem
Conventional analog-to-digital converters (ADCs) face settling errors during initial stages of conversion due to insufficient settling time, leading to incorrect determination of the most significant bit (MSB) of the digital output signal.
Innovation Solution
Incorporating a correction control circuit that adjusts the least significant bit (LSB) of the digital output signal based on comparison results, and using different clock frequencies or dual DAC types for upper and lower bit determination to mitigate settling errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the DAC generates conversion voltage with large swing width at initial stage, then the conversion range covers the full input voltage range, but the settling time becomes insufficient causing settling errors
Solution Approach 1:
The conversion process is divided into two stages: initial conversion phase and correction phase. The DAC operation is segmented into normal mode (for bits 3-1) and correction mode (for bit 0), allowing different swing widths at different times to resolve the contradiction between coverage and precision
Solution Approach 2:
The MSB is determined first in the initial conversion phase, establishing a preliminary digital output that may contain errors. Then the correction phase adjusts the LSB based on comparing the initial conversion result with the actual input voltage, preliminarily identifying and correcting the settling error
2Productivity
If the conversion process is completed quickly, then the conversion speed increases, but the settling time becomes insufficient leading to incorrect MSB determination
Solution Approach 1:
The conversion is segmented into rapid initial conversion (determining bits 3-1 quickly) followed by a correction phase (adjusting bit 0). This segmentation allows the system to prioritize speed for most bits while dedicating specific correction time to ensure reliability of the final result
Solution Approach 2:
The comparator continuously compares the DAC output voltage with the input voltage during the correction phase. This feedback mechanism identifies whether the initial MSB determination was correct and guides the adjustment of the LSB to achieve the correct final digital output
Data Source
AI summary
An analog-to-digital converter includes a comparator configured to compare an input voltage and a conversion voltage and to generate a comparison result; a digital-to-analog converter configured to generate the conversion voltage according to a digital output signal; and a control circuit including a conversion control circuit configured to determine the digital output signal corresponding to the input voltage based on the comparison result; and a correction control circuit configured to correct an error of the digital output signal by increasing or decreasing the digital output signal based on the comparison result after the digital output signal is determined.