First-Stage DAC Mismatch Correction in High-Speed MASH ADCs
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Solution Overview
Problem
Multi-stage noise shaping (MASH) delta-sigma analog-to-digital converters (ADCs) face challenges in adequately correcting errors from the feedback digital-to-analog converter (DAC), particularly in high-speed applications, where the limited linearity of the main feedback DAC impacts overall ADC performance and is not effectively shaped by the modulator.
Innovation Solution
A mechanism is introduced to digitally correct for the static mismatch of the DAC in the first stage of a MASH ADC by adding the estimated error at the output of the first stage and filtering it before the digital noise-transfer function of the second stage, allowing the DAC errors to be processed separately by the analog and digital noise transfer functions, effectively canceling them.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the main feedback DAC is used in a MASH ADC, then the ADC can operate at high speed, but the limited linearity of the DAC causes errors that are not effectively shaped by the modulator
Solution Approach 1:
The patent segments the error correction process into two independent paths: an analog correction path that processes DAC errors through the analog noise transfer function, and a digital correction path that processes the same errors through the digital noise transfer function. This segmentation allows each path to be optimized independently for high-speed operation while maintaining precision.
Solution Approach 2:
The patent introduces an intermediary correction mechanism that injects corrected error signals into both the analog and digital domains. This intermediary correction path acts as a mediator that separates the error processing from the main conversion path, allowing high-speed operation while improving linearity through dedicated correction circuits.
2Measurement precision
If traditional error correction methods are used, then DAC errors can be reduced, but the correction requires knowledge of the error transfer function which complicates the system
Solution Approach 1:
The patent implements feedback mechanisms where the correction signals are generated based on the actual DAC error characteristics observed in the system. The correction paths use feedback from the quantization noise and error signals to automatically adjust and cancel DAC errors without requiring external knowledge of the error transfer function.
Solution Approach 2:
The correction system is self-sufficient, using its own internal error signals and quantization noise to generate correction terms. The analog and digital correction paths automatically adapt to the DAC characteristics through self-generated feedback, eliminating the need for external error transfer function information or complex calibration procedures.
Data Source
AI summary
The present disclosure describes a mechanism to digitally correct for the static mismatch of the digital-to-analog converter (DAC) in at least the first-stage of a multi-stage noise shaping (MASH) analog-to-digital converter (ADC). The correction is applicable to continuous-time implementations, and is especially attractive for high-speed applications.