Dual-Quantizer ADC Feedback Loop for Lower Quantization Noise
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Solution Overview
Problem
Analog-to-digital converters with dual in-loop quantization face challenges in reducing quantization noise and manipulating the signal transfer function, making it difficult to achieve fast response times and large bandwidth.
Innovation Solution
The proposed solution involves an analog-to-digital converter with a feedback loop that includes a first quantizer, an error signal generation block, an analog loop filter, a second quantizer, a digital loop filter, and a recombiner block with recombination filters and an adder circuit to reduce quantization noise and allow for a more responsive output signal transfer function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dual in-loop quantization is used to reduce quantization noise, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The converter is divided into two separate quantization stages: a first quantizer that operates on the analog input signal and a second quantizer that operates on the filtered error signal. This segmentation allows each quantizer to be optimized independently, reducing overall quantization noise while managing complexity through functional decomposition
Solution Approach 2:
The second quantizer is nested within the feedback loop structure, operating on the error signal after analog filtering. This nested arrangement allows the quantization noise from the first quantizer to be shaped and reduced by the second quantizer's action on the error signal, achieving noise reduction while maintaining a structured, manageable architecture
2Productivity
If the signal transfer function is made equal to one for large bandwidth, then productivity is improved, but quantization noise reduction becomes more difficult
Solution Approach 1:
A feedback path is introduced that feeds the output of the second quantizer back through a digital filter to the input of the first quantizer. This feedback mechanism allows the system to maintain a signal transfer function of one (unity gain) across a wide bandwidth while simultaneously shaping and reducing quantization noise through the coordinated action of both quantizers and their associated filters
Solution Approach 2:
The system dynamically adjusts the transfer functions of the analog and digital filters to achieve a signal transfer function equal to one while maintaining quantization noise reduction. By changing the filter parameters and characteristics, the system optimizes both bandwidth/response speed and noise performance simultaneously
3Ease of manufacture
If the number of feedback bits is limited to simplify non-linearity problems, then ease of manufacture is improved, but measurement precision deteriorates
Solution Approach 1:
An analog loop filter is introduced as an intermediary between the first quantizer and the second quantizer. This analog filter processes the error signal before it reaches the second quantizer, allowing the system to achieve high effective resolution without requiring a high-resolution feedback DAC. The analog filter mediates the signal processing, enabling simplified feedback paths while maintaining measurement precision
Solution Approach 2:
The system replaces the need for a high-resolution digital feedback DAC with an analog filtering approach. Instead of using a complex multi-bit feedback DAC that would require many feedback bits, the system uses analog loop filtering combined with dual quantization to achieve the same resolution effect, thereby simplifying the feedback path and reducing non-linearity problems
Data Source
AI summary
An analog-to-digital converter comprises a first quantizer arranged for yielding a first digital signal; an error signal generation block arranged for generating an error signal representative of a difference between an analog input signal and the first digital signal; an analog loop filter arranged for receiving the error signal; a second quantizer arranged for receiving an output signal of the analog loop filter and for outputting a second digital signal; a digital loop filter arranged for receiving the second digital signal and for providing an input signal to the first quantizer; and a recombiner block comprising a first recombination and a second recombination filter, and an adder circuit for adding outputs of the first and second recombination filters. The first and second recombination filters are selected to obtain an analog-to-digital converted output signal being less dependent on quantization noise caused by the first quantizer than a first digital signal.