Comparator Offset Cancellation With Pregain Feedback Stages
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Solution Overview
Problem
Conventional comparators face challenges in achieving high precision due to offset errors, which are not effectively addressed by existing offset correction methods, especially in semiconductor fabrication processes, affecting their performance in applications like SAR ADCs.
Innovation Solution
The proposed solution involves a comparator design with multiple pregain stages and a switch network that provides feedback paths for offset cancellation, using capacitors and switches controlled by clock signals to minimize offset errors, making the design compatible with various semiconductor processes and reducing sensitivity to fabrication variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional offset correction methods are used in comparators, then the circuit structure remains simple, but the precision is insufficient due to offset errors not being effectively addressed
Solution Approach 1:
The comparator is divided into multiple pregain stages (first pregain stage, second pregain stage, and optionally third pregain stage) with distinct functions. Each stage processes the signal differently, allowing offset cancellation in later stages while maintaining signal amplification in earlier stages. This segmentation enables precise offset correction without requiring complete redesign of the entire comparator structure.
Solution Approach 2:
A feedback path is introduced that connects the output of the third pregain stage back to the input of the second pregain stage through a switch network. This feedback mechanism allows the comparator to sense and correct offset errors by feeding back correction signals to previous stages, effectively canceling offsets while maintaining the overall comparator functionality.
2Measurement precision
If multiple pregain stages are added for offset cancellation, then offset errors are reduced, but the device complexity increases
Solution Approach 1:
The switch network performs multiple functions: it enables the feedback path for offset cancellation, controls the timing of signal transmission between stages, and can be configured to connect different stages based on operational requirements. This multi-functionality reduces the need for separate dedicated components for each function, thereby limiting the increase in overall device complexity despite adding multiple pregain stages.
Solution Approach 2:
The feedback path is configured to act preliminarily by feeding back offset correction signals from later stages to earlier stages before the final comparison occurs. This preliminary action allows offset errors to be cancelled in advance during the pregain stages, preventing them from affecting the final comparison result and reducing the need for complex post-processing correction circuits.
3Measurement precision
If feedback paths are introduced for offset cancellation, then precision is improved, but the sensitivity to fabrication variations increases
Solution Approach 1:
The switch network introduces dynamic control to the feedback path, allowing the comparator to switch between different operational modes (with or without feedback, different stage configurations) based on the specific operational requirements. This dynamic adaptability enables the circuit to optimize its performance for offset cancellation in normal operation while potentially reducing sensitivity to fabrication variations by adjusting the feedback configuration when needed.
Solution Approach 2:
The feedback path allows for dynamic adjustment of operational parameters such as gain distribution across stages, feedback timing, and signal routing. By changing these parameters adaptively, the comparator can optimize offset cancellation performance while compensating for fabrication variations. The ability to adjust parameters like feedback timing and stage gain distribution helps mitigate the impact of manufacturing tolerances on overall precision.
Data Source
AI summary
An apparatus includes a comparator. The comparator includes first and second pregain stages, and a switch network coupled to the first and second pregain stages. A plurality of switches in the switch network are operable to provide a feedback path around at least one of the first and second pregain stages. The comparator further includes a latch coupled to the second pregain stage.