Sigma-Delta ADC Real-Time DAC Mismatch Correction
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Solution Overview
Problem
Sigma-delta analog-to-digital converters with multi-bit quantization suffer from non-linearity due to DAC element mismatch, leading to degraded performance and signal-to-noise ratio, primarily caused by static element mismatch and input signal-dependent tones.
Innovation Solution
A digital process estimates the unit current element mismatch error by correlating a scrambled thermometer coded signal with the quantization output signal, using a replica DAC circuit to digitally model and correct the non-ideal DAC operation, thereby eliminating the DAC error and improving the ADC output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multi-bit quantization is used in sigma-delta modulator, then resolution and sampling rate performance is improved, but DAC element mismatch non-linearity degrades signal-to-noise ratio
Solution Approach 1:
The patent applies preliminary action by estimating DAC element mismatch errors before they degrade the signal-to-noise ratio. The error estimation circuit continuously predicts mismatch errors using correlation between scrambled thermometer codes and quantization output, and the replica DAC pre-compensates for these errors in the feedback path, preventing non-linearity from corrupting the ADC output before it affects performance metrics.
Solution Approach 2:
The patent implements feedback through the replica DAC circuit that mirrors the actual DAC's mismatch characteristics. The estimated error signals are fed back through the replica DAC to cancel out the non-linearity effects in real-time, creating a closed-loop compensation system that maintains signal-to-noise ratio while preserving multi-bit quantization benefits.
2Manufacturing precision
If DAC element mismatch correction is implemented, then non-linearity is reduced, but device complexity increases due to additional correction circuits
Solution Approach 1:
The patent uses copying by creating a replica DAC circuit that replicates the mismatch characteristics of the actual DAC without requiring precise physical matching. The replica DAC is programmed with estimated error values to simulate the non-ideal behavior, allowing digital compensation without duplicating the entire DAC structure in analog form, thus reducing complexity while maintaining correction effectiveness.
Solution Approach 2:
The patent applies mechanics substitution by replacing complex analog mismatch correction circuits with digital error estimation and compensation mechanisms. Instead of using analog components to physically correct DAC non-linearity, the system uses digital correlation-based error estimation and programmable replica DAC to achieve correction, simplifying the overall circuit architecture while improving linearity.
Data Source
AI summary
An estimate of unit current element mismatch error in a digital to analog converter circuit is obtained through a correlation process. Unit current elements of the digital to analog converter circuit are actuated by bits of a thermometer coded signal generated in response to a quantization output signal. A correlation circuit generates the estimates of the unit current element mismatch error from a correlation of a first signal derived from the thermometer coded signal and a second signal derived from the quantization output signal.