Image Sensor Test Circuit Dynamic Reset Code
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Solution Overview
Problem
Existing image sensors lack an effective method to detect errors in the counting operation of counters during testing, which is crucial for producing clear image data.
Innovation Solution
An image sensor with a test circuit that generates a count clock signal and changes a reset code based on a horizontal time period, allowing for the testing of counting operations by comparing a second counting value with a test code, thereby detecting errors in the counter's operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed reset code is used in the counter testing, then the test circuit is simple, but the test coverage and accuracy are insufficient to detect various counter defects
Solution Approach 1:
The reset code is changed from a fixed value to a dynamic value that varies with the horizontal time period. The test circuit automatically adjusts the reset code based on the current horizontal timing, enabling the detection of different counter defects at different test stages without requiring multiple fixed test configurations.
Solution Approach 2:
The reset code parameter is made variable instead of constant. By changing the reset code according to the horizontal time period, the test circuit can detect various counter defects that would remain hidden with a fixed reset code, thereby improving test coverage without adding complex external test equipment.
2Measurement precision
If the reset code is changed according to horizontal time period, then the detection accuracy of counter defects is improved, but the test circuit complexity increases
Solution Approach 1:
The test circuit uses the existing horizontal time period signal from the image sensor's normal operation to automatically adjust the reset code. This self-service approach allows the test circuit to leverage existing timing information rather than requiring external complex timing generation equipment, thus improving detection accuracy while minimizing added complexity.
Solution Approach 2:
The test circuit serves multiple functions by using the same horizontal time period signal for both normal image sensor operation and for adjusting the reset code during testing. This multi-functionality reduces the need for separate dedicated test timing circuits, thereby improving detection accuracy without proportionally increasing circuit complexity.
Data Source
AI summary
Provided is an image sensor including a pixel array that includes a plurality of pixels, wherein each of the plurality of pixels is configured to generate an analog signal in response to incident light; an analog-to-digital converter that includes a counter, wherein the analog-to-digital converter is configured to convert the analog signal into a digital signal; and a test circuit that is configured to change a reset code according to a horizontal time period, wherein the reset code corresponds to a first counting value during a reset time period of a test mode according to a count clock signal, and wherein the test circuit is configured to test a counting operation of the counter based on the reset code that changes according to the horizontal time period.