Image Sensor Test Circuit for ADC Counter Clock Verification
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Solution Overview
Problem
Existing image sensors lack an effective method for testing the counting operations of their analog-to-digital converters (ADCs), which is crucial for generating clear image data, as they rely on complex comparator and counter systems without a straightforward testing mechanism.
Innovation Solution
Incorporating a test logic circuit within the image sensor that receives a test code, generates a count clock signal, and tests the counting operation of the counter, allowing for the external output of a test result through a test terminal, enabling direct verification of the ADC's performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a complex comparator and counter system is used for ADC, then conversion accuracy is improved, but testing complexity increases
Solution Approach 1:
The test logic extracts the testing function from the main ADC operation by providing a dedicated test mode. When the test mode signal is activated, the system separates the counting operation testing from normal image conversion, allowing independent verification of counter functionality without affecting the main conversion accuracy.
Solution Approach 2:
The system changes the operational parameters by switching between normal mode and test mode through the test mode signal. In test mode, the ADC operates with specific parameters (test code input, count clock signal generation) that enable counting verification, while maintaining the ability to switch back to normal conversion parameters.
2Device complexity
If no dedicated test circuit is added, then device complexity is reduced, but testing capability is lost
Solution Approach 1:
The test logic is designed with multi-functionality, serving both as part of the normal ADC operation and as a dedicated testing mechanism. The same counter and comparator circuits are used for both image conversion and counting operation testing, eliminating the need for completely separate test hardware while maintaining testing capability.
Solution Approach 2:
The test logic acts as an intermediary component that bridges the gap between the existing ADC circuitry and the testing requirement. It provides the test code input, generates the count clock signal, and outputs test results, thereby enabling testing of the counter without requiring fundamental changes to the core ADC architecture.
3Device complexity
If test mode is integrated into existing ADC, then additional hardware is minimized, but operation complexity increases
Solution Approach 1:
The test logic performs self-service by automatically generating the count clock signal from the test code input and autonomously conducting the counting operation testing. The system self-verify the counter functionality by comparing the counting results with expected values, reducing the need for external test equipment and simplifying the operation for users.
Data Source
AI summary
An image sensor includes a pixel array, an analog-to-digital converter (ADC), and a test circuit. The pixel array includes a plurality of pixels arranged in rows and columns. Each pixel generates an analog signal based on incident light. The ADC converts the analog signal to a digital signal using a counter. The test circuit receives a test code in a test mode, generates a count clock signal based on the test code, tests a counting operation of the counter according to the count clock signal, and externally outputs a test result of the counter through a test terminal.