SAR ADC Noise Shaping with Dual Capacitive DAC Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing noise shaping methods for successive approximation register (SAR) analog-to-digital converters (ADCs) require large capacitors or complex filtering, leading to increased size and complexity, which is inefficient and costly.
Innovation Solution
Implementing a SAR ADC with two capacitive digital-to-analog converters (DACs) and a comparator, using a switch circuit to alternate between feedback and compare modes, allowing residue voltage transfer between conversion cycles for noise shaping without requiring large capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing noise shaping methods are used in SAR ADCs, then quantization noise is reduced, but capacitor size increases and device complexity increases
Solution Approach 1:
The patent divides the single capacitive DAC into two separate capacitive DACs (first and second capacitive DACs). Each DAC handles different aspects of the conversion process, allowing noise shaping functionality to be implemented without requiring a single large capacitor. This segmentation reduces the size requirement while maintaining noise shaping capability.
Solution Approach 2:
The patent implements dynamic switching between two capacitive DACs using a switch circuit. The system alternates between using the first capacitive DAC and the second capacitive DAC for different conversion cycles. This dynamic operation enables noise shaping through the alternating feedback paths without requiring large static capacitor values, thereby reducing overall device complexity.
2Measurement precision
If existing noise shaping methods are used in SAR ADCs, then quantization noise is reduced, but capacitor size increases
Solution Approach 1:
The patent segments the capacitive DAC into two separate capacitive DACs with smaller individual capacitor values. By dividing the functionality across two smaller capacitors rather than using one large capacitor, the patent achieves noise shaping while reducing the total area occupied by capacitive elements in the circuit.
Solution Approach 2:
The dynamic switching between two capacitive DACs allows the system to achieve noise shaping with smaller capacitor values. The alternating use of first and second capacitive DACs enables the implementation of noise shaping feedback without requiring large static capacitor values, thereby reducing the area requirement.
3Area of stationary object
If two capacitive DACs are used with switching, then noise shaping is achieved without large capacitors, but circuit complexity increases
Solution Approach 1:
The comparator is designed to serve multiple functions: it acts as a comparison element during normal conversion cycles and as a feedback element during noise shaping cycles. The same comparator circuit is used for both comparing analog inputs and providing feedback for noise shaping, eliminating the need for separate feedback amplifiers and reducing overall circuit complexity despite using two capacitive DACs.
Solution Approach 2:
The switch circuit dynamically connects and disconnects the two capacitive DACs and the comparator in different configurations. This dynamic switching allows the system to alternate between standard conversion mode and noise shaping mode, achieving noise shaping functionality with smaller capacitors while managing circuit complexity through time-multiplexed operation.
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
In certain aspects, an analog-to-digital converter includes a first capacitive digitalto- analog converter (DAC), a second capacitive DAC, and a comparator including a first input, a second input, and an output. The analog-to-digital converter also includes a switch circuit including a first input coupled to the first capacitive DAC, a second input coupled to the second capacitive DAC, a first output coupled to the first input of the comparator, and a second output coupled to the second input of the comparator. The analog-to-digital converter further includes a first switch coupled between the output of the comparator and the first input of the comparator, and a successive approximation register (SAR) coupled to the output of the comparator, the first capacitive DAC, and the second capacitive DAC.