Sigma-Delta ADC Feedback DAC Copy for Mismatch Linearity
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Solution Overview
Problem
Sigma-delta modulator circuits with multi-bit quantization face non-linearity issues due to mismatch errors in digital-to-analog converter (DAC) circuits, leading to degraded signal-to-noise ratio (SNR) and distorted modulator outputs.
Innovation Solution
A digital DAC copy circuit is introduced to replicate the non-ideal operation of the N-bit DAC, generating P-bit code words that account for unit element errors, effectively correcting the mismatch errors and improving the SNR by noise shaping the quantization and mismatch errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multi-bit quantization is used in sigma-delta modulator circuits, then the resolution and sampling rate performance is improved, but non-linearity issues arise due to mismatch errors in DAC circuits
Solution Approach 1:
The patent creates a digital copy of the feedback DAC circuit that replicates its non-ideal behavior. This digital copy generates correction codes that compensate for the mismatch errors in the actual DAC, allowing the system to maintain both high resolution and linearity by canceling out the harmful non-linear effects through the copied model
Solution Approach 2:
The patent implements a feedback mechanism where the digital copy of the DAC continuously monitors and compensates for mismatch errors. The correction codes generated from the digital copy are fed back to correct the quantization process, enabling the system to maintain high resolution while eliminating the non-linearity problems that would otherwise degrade performance
2Measurement precision
If multi-bit quantization is used, then signal-to-noise ratio should improve, but mismatch errors in DAC circuit degrade the SNR
Solution Approach 1:
The patent converts the harmful mismatch errors into a beneficial correction mechanism. By digitally copying the DAC's non-ideal behavior and using it to generate correction codes, the system transforms the harmful mismatch errors into useful information that actively compensates for and cancels out the degradation, thereby improving the overall signal-to-noise ratio
3Productivity
If N-bit DAC circuit is used in feedback loop, then multi-bit quantization benefits are achieved, but unit element mismatch causes non-linearity
Solution Approach 1:
The patent creates a digital replica of the N-bit DAC circuit that captures the actual non-ideal behavior of the unit elements. This copy is used to generate correction codes that compensate for manufacturing variations, allowing the system to maintain high quantization efficiency while correcting for the inevitable mismatches that occur during manufacturing
Solution Approach 2:
The patent changes the parameter representation from ideal uniform steps to actual measured unit element values. By storing and using the actual mismatch parameters of each unit element in the digital copy, the system adapts to the real-world manufacturing variations and compensates for them through calculated correction codes
Data Source
AI summary
A sigma-delta modulator includes an N-bit quantization circuit that generates a stream of N-bit code words and a feedback signal path with an N-bit DAC circuit, having a non-ideal operation due to mismatch error, that converts the stream of N-bit code words to generate a feedback signal. A digital DAC copy circuit provides a digital replication of the N-bit DAC circuit. The digital replication accounts for the non-ideal operation of the N-bit DAC circuit 126 due to mismatch error, and converts the stream of N-bit code words to generate a stream of P-bit code words, where P>N, that are functionally equivalent to the feedback signal output from the N-bit DAC circuit.