Stochastic ADC Feedback Loops for Comparator Offset Linearity
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Solution Overview
Problem
Stochastic analog-to-digital converters (ADCs) face issues with poor linearity due to comparator offsets and mismatched reference signals, which degrade performance and limit the benefits of using small transistors for reduced power consumption and increased speed.
Innovation Solution
The proposed ADC incorporates a feedback loop and filter configuration that reduces the difference between quantizer outputs and reference signals at specific frequency regions, using single-bit quantizers and low-pass filters to mitigate the effects of comparator offsets and distribute them as pseudo-dithering signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If comparator offsets are used as references in stochastic ADC, then transistor size can be reduced for increased speed and reduced power consumption, but linearity performance degrades due to Gaussian distribution mismatch of comparator offsets
Solution Approach 1:
The patent introduces feedback loops that use digital-to-analog converters (DACs) to generate correction signals based on the quantizer outputs. These feedback signals are subtracted from the input signal before being applied to the comparators, effectively compensating for the Gaussian distribution mismatch of comparator offsets and improving linearity while maintaining the benefit of small transistor sizes
Solution Approach 2:
The patent transforms the comparator offset distribution from a problematic Gaussian distribution to a desired uniform distribution through the feedback mechanism. By dynamically adjusting the reference signals based on quantizer outputs, the system changes the statistical parameters of the offset distribution to achieve better linearity performance
2Measurement precision
If dithering signals are used as comparator references to improve linearity, then linearity performance improves, but comparator offsets must be kept small which limits the benefit of using small transistors
Solution Approach 1:
The patent replaces traditional dithering signals with feedback-generated correction signals that are adaptively adjusted based on quantizer outputs. This feedback mechanism achieves linearity improvement without requiring small comparator offsets, thereby allowing the use of small transistors for high-speed operation
Solution Approach 2:
The patent introduces DACs and feedback paths as intermediary elements between the quantizer outputs and the comparator inputs. These intermediaries generate correction signals that mediate the interaction between quantizer outputs and comparator references, achieving linearity improvement without direct reliance on small comparator offsets
3Measurement precision
If feedback loops are added to correct comparator offset effects, then linearity improves, but device complexity increases due to additional components
Solution Approach 1:
The patent designs the feedback loops to serve multiple functions: they generate correction signals for linearity improvement, shape noise spectral density, and enable high-speed operation. The same feedback infrastructure achieves multiple objectives, reducing the need for separate dedicated circuits for each function
Solution Approach 2:
The patent divides the feedback correction into multiple parallel loops, each handling a specific quantizer output. This segmentation allows independent optimization of each feedback path and enables modular implementation, reducing overall system complexity through systematic decomposition
Data Source
AI summary
An analog to digital converter has an input, a plurality of quantizers, a plurality of feedback loops, and a plurality of filters. The input is configured to receive an input signal. The plurality of quantizers has the Nth quantizer, and the Nth quantizer has the Nth quantizer input and the Nth quantizer output. The Nth quantizer input is connected to the input. The plurality of feedback loops has the Nth feedback loop, and the Nth feedback loop is formed around the Nth quantizer output and the Nth quantizer input and configured to reduce the difference between the signal of the Nth quantizer output and an Nth reference signal at an Nth frequency region. The plurality of filters has an Nth filter. The Nth filter is configured to select the Nth frequency region. The feedback loops provide a way to control the effect of some nonidealities such as comparator offsets.