MASH ADC DAC Mismatch Cancellation for High-Speed Linearity
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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 non-linear feedback digital-to-analog converters (DACs), which affect the overall performance and linearity of the ADCs, especially in high-speed applications.
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 second stage, allowing the DAC errors to be processed separately by the analog and digital noise transfer functions, effectively cancelling them from the output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital correction schemes are used to cancel DAC errors in multi-stage noise shaping ADCs, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The correction mechanism is segmented into stage-specific components where each stage processes and corrects DAC errors independently. The first stage generates a correction signal that is selectively applied to subsequent stages, allowing localized error correction without requiring system-wide complexity. This segmentation enables the SNDR improvement from 72.7 dB to 90.6 dB while keeping the correction mechanism manageable in complexity.
Solution Approach 2:
The correction signal is generated in advance at the output of the first stage before being propagated through subsequent stages. By preparing the correction signal early in the conversion process, the mechanism prevents DAC errors from propagating through the entire system, thereby improving measurement precision without requiring complex real-time correction at each stage.
2Reliability
If feedback DAC errors are corrected in high-speed applications, then reliability is improved, but productivity decreases
Solution Approach 1:
An intermediary correction signal is introduced that mediates between the feedback DAC output and the subsequent conversion stages. This correction signal acts as a bridge that eliminates DAC errors without requiring reconfiguration of the high-speed conversion path, thereby maintaining productivity while improving reliability through enhanced conversion accuracy.
Solution Approach 2:
The correction signal is prepared in advance at the first stage output, allowing subsequent stages to process corrected signals at full speed without interruption. This preliminary correction approach ensures that reliability is improved through error cancellation while the high-speed conversion pipeline remains uninterrupted, maintaining productivity.
Data Source
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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.