SAR ADC R-DAC Architecture for Self-Diagnosis Accuracy
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Solution Overview
Problem
Existing analog to digital converters (ADCs) lack effective self-diagnosis capabilities, particularly in applications requiring functional safety, due to limitations in internal test DACs, such as reduced resolution and accuracy.
Innovation Solution
The proposed ADC architecture includes two digital to analog converters (DACs) and a switch matrix, allowing for capacitively coupling the input signal or the DAC outputs between the comparator inputs, enabling self-diagnosis by averaging linearity errors in functional mode and detecting errors affecting individual DACs in test mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an internal test DAC is implemented inside the ADC, then basic functionality checking is enabled, but the resolution and accuracy are reduced making it unsuitable for functional safety applications
Solution Approach 1:
The patent divides the single DAC function into two separate DACs: a first DAC for normal conversion operations and a second DAC for test operations. This segmentation allows each DAC to be optimized for its specific purpose, with the second DAC dedicated solely to testing functions requiring high precision, while the first DAC handles general conversion tasks.
Solution Approach 2:
The patent creates a multi-functional system where the second DAC serves dual purposes: it acts as a test signal source for self-diagnosis and can also function as an additional conversion channel. The switch matrix enables the second DAC to be capacitively coupled to the comparator input during test modes, providing both testing capability and potential conversion functionality.
2Area of stationary object
If a test mode using the existing DAC is implemented, then area and cost are saved, but leakage current errors cannot be detected reducing reliability
Solution Approach 1:
The patent separates the test function from the conversion function by implementing a dedicated second DAC. This allows the test signal path to be independent from the conversion path, enabling detection of leakage current errors that would affect only one path but not the other, thereby improving error detection capability.
Solution Approach 2:
The patent introduces a switch matrix as an intermediary component that enables flexible routing between the input signal, the two DACs, and the comparator. This intermediary structure allows the system to switch between different operational modes (normal conversion, test mode with first DAC, test mode with second DAC) without requiring separate physical paths.
3Reliability
If two DACs are implemented for self-diagnosis, then error detection capability is improved, but device complexity increases
Solution Approach 1:
The patent designs the second DAC to serve multiple functions: it acts as a test signal source for self-diagnosis, can be routed to the comparator for testing, and potentially serves as an additional conversion channel. This multi-functionality justifies the added complexity by providing both testing and conversion capabilities from a single component.
Solution Approach 2:
The patent combines the test signal generation and conversion functions within the same ADC architecture by integrating the second DAC and switch matrix. This merging allows the system to perform both testing and conversion operations without requiring completely separate systems, thereby managing complexity while achieving self-diagnosis capability.
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 architecture enables ADCs to be used in functional safety applications by providing effective self-diagnosis capabilities without increasing area or power consumption, and allows for detection of errors affecting only one DAC, ensuring reliable operation.
Implementation Method 1
a switch matrix, configured for capacitively coupling the input signal between a first input and a second input of the comparator, or for capacitively coupling an output signal of the first DAC or an output signal of the second DAC or both between the first input and the second input of the comparator
Data Source
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AI summary
An ADC (100) for converting an input signal into a digital value. In the ADC (100) a successive approximation register (110) is connected with its output to a first DAC (120A), to a second DAC (120B). A switch matrix (130) is configured for capacitively coupling the input signal between the first input and the second input of the comparator (150) or for capacitively coupling an output signal of the first DAC (120A) or an output signal of the second DAC (120B) or both between the first input and the second input of the comparator (150). The ADC (100) comprises a comparator switch (160) between the first and the second input of the comparator (150). An output of the comparator (150) is connected to an input of the successive approximation register (110).