Two-Step Hybrid ADC Using CDS for Accurate Nyquist LSB Conversion
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Solution Overview
Problem
Two-step hybrid analog-to-digital converters (ADCs) face challenges in accurately scaling reference voltages during the Nyquist conversion step due to inaccuracy in chopping, leading to non-linearity and ineffective removal of offset noise, as chopping lacks a filtering mechanism for up-converted offset and flicker noise.
Innovation Solution
Implementing a hybrid ADC that uses chopping for Delta-Sigma conversion to resolve most significant bits (MSBs) and Correlated Double Sampling (CDS) for Nyquist conversion to resolve least significant bits (LSBs), combining the results to generate a digital output signal, thereby leveraging the power efficiency of chopping while ensuring accurate scaling and noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If chopping is applied in the Nyquist portion for reference scaling, then power consumption is reduced, but measurement precision deteriorates due to non-linearity from inaccurate scaling and ineffective offset removal
Solution Approach 1:
The patent divides the ADC into two distinct portions: a Delta-Sigma portion that uses chopping for MSB conversion, and a Nyquist portion that uses CDS for LSB conversion. This segmentation allows each portion to use the most appropriate technique for its specific function, resolving the contradiction by applying chopping where power efficiency is critical (MSB stage) and CDS where precision is critical (reference scaling stage).
Solution Approach 2:
The patent applies different noise reduction techniques to different parts of the conversion process: chopping is applied in the Delta-Sigma portion for MSB conversion where power consumption is the primary concern, while CDS is applied in the Nyquist portion for reference scaling where measurement precision is the primary concern. This local differentiation of techniques resolves the contradiction between power efficiency and precision.
2Device complexity
If chopping is used for reference scaling in the second step, then device complexity is reduced, but manufacturing precision deteriorates due to non-linearity from inaccurate reference scaling
Solution Approach 1:
The patent segments the reference scaling function from the chopping operation by using CDS specifically for reference scaling in the Nyquist portion. This segmentation ensures that reference scaling accuracy is maintained through CDS while keeping the overall device complexity manageable by using simpler chopping in the Delta-Sigma portion.
Solution Approach 2:
The patent applies CDS specifically to the reference scaling operation in the Nyquist portion where manufacturing precision is critical, while using simpler chopping in the Delta-Sigma portion where device complexity is more of a concern. This local application of techniques optimizes the balance between complexity and precision.
3Speed
If Nyquist conversion is used for LSBs in a two-step hybrid ADC, then conversion speed is improved, but noise susceptibility increases due to lack of effective filtering for up-converted offset
Solution Approach 1:
The patent segments the noise handling function between the two conversion steps: the Delta-Sigma portion with chopping handles offset and flicker noise through up-conversion and filtering for MSBs, while the Nyquist portion with CDS handles reference noise for LSBs. This segmentation allows fast Nyquist conversion to proceed while noise is managed by the preceding Delta-Sigma stage.
Solution Approach 2:
The patent applies preliminary noise reduction through chopping and filtering in the Delta-Sigma portion before the Nyquist conversion takes place. This preliminary action removes or attenuates offset and flicker noise before the fast Nyquist conversion, allowing the speed advantage of Nyquist to be realized without the full burden of noise susceptibility.
Data Source
AI summary
A two-step, hybrid analog-to-digital converter (ADC) includes a Delta-Sigma ADC that employs chopping to resolve MSBs, a Nyquist ADC that employs correlated double sampling (CDS) to resolve LSBs, and a combiner that combines the MSBs and the LSBs to generate a digital output signal. The Delta-Sigma ADC has first and second integrators where, after resolving the MSBs, the first integrator is re-configured to function as a reference buffer for the Nyquist ADC and the second integrator is re-configured to function as the Nyquist ADC.