Charge Redistribution DAC With On-Chip Reservoir for Faster Settling
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Solution Overview
Problem
Charge redistribution digital-to-analog converters (DACs) in integrated circuits are limited by parasitic inductance, which restricts their settling speed, especially in high-speed applications like successive approximation (SAR) ADCs.
Innovation Solution
Incorporating an on-chip reservoir capacitor that samples external reference voltages and disconnects from them during operation, allowing charge redistribution to occur entirely on-chip, thereby isolating the DAC from parasitic effects and improving settling speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional external reference voltages are used in charge redistribution DAC, then the DAC can operate with simple structure, but the parasitic inductance limits the settling speed
Solution Approach 1:
The patent extracts the harmful parasitic inductance by moving the charge redistribution process entirely onto the IC chip. The reservoir capacitor and DAC capacitors are both on-chip components, eliminating the need for external reference voltage connections that introduce parasitic inductance. This extraction of the harmful element (external connections) while retaining the useful function (charge redistribution) resolves the contradiction between simple structure and high settling speed.
Solution Approach 2:
The patent introduces an on-chip reservoir capacitor as an intermediary component. This reservoir capacitor serves as a local charge source that mediates between the digital control signals and the DAC output, eliminating the need for external reference voltage connections. The intermediary reservoir capacitor enables fast charge redistribution on-chip while maintaining electrical neutrality, thus improving settling speed without compromising the DAC's fundamental operation.
2Speed
If charge redistribution is performed entirely on-chip, then settling speed is improved, but the device complexity increases due to additional on-chip components
Solution Approach 1:
The reservoir capacitor performs multiple functions: it serves as a local charge source for the DAC, maintains electrical neutrality during charge redistribution, and eliminates the need for external reference voltage connections. By making this single component multi-functional, the patent achieves fast on-chip operation without proportionally increasing device complexity. The reservoir capacitor's multiple roles justify its integration while delivering significant performance benefits.
Solution Approach 2:
The on-chip reservoir capacitor enables the DAC to be self-sufficient by providing all necessary charge locally without external references. The reservoir capacitor automatically maintains electrical neutrality and supplies charge during redistribution operations, making the DAC independent of external components. This self-service capability achieves fast settling speed while the complexity is limited to a single integrated capacitor rather than multiple external components and connections.
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 enhances the settling speed of the DAC by eliminating the impact of external parasitics, limiting performance only by switch on-resistance, and achieving faster charge redistribution, particularly beneficial for SAR ADCs.
Implementation Method 1
a reservoir capacitor CRES having a first side and a second side, and means for sampling the first and second reference voltages to the reservoir capacitor
Implementation Method 2
charge redistribution digital-to-analog converter (DAC) that may carry on a charge redistribution entirely on an IC chip
Data Source
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AI summary
Embodiments of the present disclosure may provide a charge redistribution DAC with an on-chip reservoir capacitor to provide charges to the DAC in lieu of traditional external reference voltages. The DAC may include the on-chip reservoir capacitor having a first plate and a second plate, an array of DAC capacitors to generate a DAC output, and an array of switches controlled by a DAC input word to couple the DAC capacitors to the reservoir capacitor. The charge redistribution DAC may further comprise a first switch connecting the first plate to an external terminal for a first external reference voltage, and a second switch connecting the second plate to an external terminal for a second external reference voltage. One embodiment may provide an ADC that includes the charge redistribution DAC.