Multi-Level Sigma-Delta Modulator With Switched Reference Feedback
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Solution Overview
Problem
Sigma-delta modulators face challenges in implementing multi-level outputs due to the difficulty in designing analog-to-digital converters (ADCs) for low input signals, especially at high sampling frequencies, which complicates the generation of accurate feedback signals.
Innovation Solution
A single-order, multi-level sigma-delta modulator design that uses a multi-level flash ADC to control analog switches, selecting from a range of reference voltages to generate feedback signals, reducing transient effects by adjusting these voltages to ensure only one changes when the ADC output switches states, thereby simplifying the ADC implementation and improving performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multi-level flash ADC is used to generate feedback signals in a sigma-delta modulator, then the modulator can achieve multi-level output capability, but the ADC implementation becomes difficult for low input signals at high sampling frequencies
Solution Approach 1:
The feedback signal generation is segmented into two stages: first, a single-level ADC converts the integrated error signal to a digital value; then, a lookup table (pre-computed array) maps this digital value to the appropriate multi-level feedback signal. This segmentation avoids the complexity of designing a multi-level ADC while achieving multi-level output capability.
Solution Approach 2:
A lookup table serves as an intermediary between the simple single-level ADC and the required multi-level feedback signals. The lookup table pre-computes and stores the mapping relationships, allowing the system to generate complex multi-level feedback without requiring a complex multi-level ADC.
2Adaptability or versatility
If traditional multi-level modulator designs are used, then multi-level output is achieved, but the design complexity increases significantly
Solution Approach 1:
Instead of directly implementing complex multi-level ADC logic, the patent uses a lookup table that copies pre-computed feedback values. The lookup table stores the mapping from integrated error signal levels to appropriate feedback levels, effectively copying the complex multi-level relationships into a simple data structure that can be accessed by a simple ADC.
3Manufacturing precision
If the integrated error signal is scaled to be very small to maintain linearity, then linearity is improved, but the ADC input signal level becomes very low making high-speed conversion difficult
Solution Approach 1:
The lookup table is pre-computed to account for the scaled input signal levels. By performing the complex multi-level mapping in advance (during table generation) rather than in real-time during operation, the system can use a simple single-level ADC operating at high speeds without compromising linearity or multi-level output capability.
Data Source
AI summary
A Sigma-Delta Modulator (SDM) has a summing junction that receives an input signal and a feedback signal, a multi-level analog-to-digital converter (ADC) that receives the SDM input signal and generates an ADC output, a first analog switch that receives the ADC output and generates a plurality of reference voltages, a second analog switch generating the feedback signal, where the feedback signal is selected from one of the reference voltages.