CT Sigma-Delta ADC Reference Circuit Without a Buffer
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Solution Overview
Problem
Existing analog-to-digital converter (ADC) technologies face challenges in delivering a precision low noise reference voltage without the need for a reference buffer, particularly in continuous-time sigma delta (CTSD) ADCs, where noise filtering and charge injection issues persist, leading to added power, area, noise, and DC errors.
Innovation Solution
The implementation of an integrated resistor divider and external capacitor to derive a low noise precision reference voltage, eliminating the need for a reference buffer by using a resistive input ADC and incorporating an additional servo amplifier to reduce common mode variation errors, thereby bandlimiting wideband noise and providing low gain error and drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a reference buffer is used to deliver precision reference voltage, then noise filtering capability is improved, but power consumption and circuit area increase
Solution Approach 1:
The patent extracts the reference buffer component from the ADC system and replaces it with an integrated resistor divider network. This removal eliminates the power consumption and area overhead of the reference buffer while maintaining noise filtering through the resistive division network combined with external capacitors.
Solution Approach 2:
The patent merges the reference voltage generation function directly into the ADC circuitry by integrating the resistor divider network within the ADC. This consolidation eliminates the need for a separate reference buffer component, reducing both power consumption and circuit area while maintaining precision through careful resistor matching and external capacitor filtering.
2Object-affected harmful factors
If a reference buffer is used to deliver precision reference voltage, then noise filtering capability is improved, but circuit area increases
Solution Approach 1:
The patent extracts the reference buffer component from the ADC system and replaces it with an integrated resistor divider network. This removal eliminates the power consumption and area overhead of the reference buffer while maintaining noise filtering through the resistive division network combined with external capacitors.
Solution Approach 2:
The patent merges the reference voltage generation function directly into the ADC circuitry by integrating the resistor divider network within the ADC. This consolidation eliminates the need for a separate reference buffer component, reducing both power consumption and circuit area while maintaining precision through careful resistor matching and external capacitor filtering.
3Measurement precision
If noise shaping techniques are applied to push quantization noise to higher frequencies, then signal-to-noise ratio in signal band is improved, but complexity of ADC circuitry increases
Solution Approach 1:
The patent segments the noise filtering function into two parts: noise shaping in the sigma-delta modulator that pushes quantization noise to higher frequencies, and external capacitor-based filtering that attenuates the shaped noise. This segmentation achieves high signal-to-noise ratio while keeping the core ADC circuitry relatively simple by offloading some filtering to external components.
Solution Approach 2:
The patent employs feedback through the sigma-delta modulator's noise shaping mechanism, where quantization noise is deliberately shaped and pushed to higher frequencies through feedback control. This feedback-based noise shaping improves signal-to-noise ratio in the signal band while maintaining manageable circuit complexity through the use of a simple 1-bit quantizer and external filtering.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precision low noise reference voltage delivery without a reference buffer, reducing power consumption, area, noise, and DC errors, while maintaining high accuracy and noise filtering capabilities.
Implementation Method 1
a voltage divider circuit internal to the ADC, the voltage divider circuit including a first resistive element coupled to a resistive input of a digital-to-analog converter (DAC)
Implementation Method 2
The implementation of an integrated resistor divider and external capacitor to derive a low noise precision reference voltage
Implementation Method 3
a switching element coupled between the second end of the first resistive element and the first end of the resistive input of the DAC, the switching element having an open state and a closed state
Data Source
AI summary
Techniques to deliver a precision low noise reference voltage to a precision analog-to-digital converter without the need of a reference buffer or digital correction. In an example, a technique can use an integrated resistor divider and external capacitor to derive a low noise precision reference voltage either from the power supply of the ADC, or from an integrated reference source.