On-chip design-for-testing structure for CMOS APS (active pixel sensor) image sensor

• US 6,797,933 B1
• Filed: 06/29/2001
• Issued: 09/28/2004
• Est. Priority Date: 06/29/2001
• Status: Expired due to Term

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Vanguard International Semiconductor Corporation
• Inventors: Shu, Tzi-Hsiung, Mendis, Sunetra K.
• Primary Examiner(s): PYO, KEVIN K
• Application Number:
  US09/896,486
• Time in Patent Office: 1,187 Days
• Field of Search: 250/208.1, 250/214.R, 250/214.A, 348/241, 348/294, 348/301, 348/302, 348/308, 348/311, 257/291, 257/292
• US Class Current: 250/208.1
• CPC Class Codes: H04N 1/00002 Diagnosis, testing or measuring; Detecting, analysing or monitoring not otherwise provided for error detection, error correction or monitoring in digital computers or digital computer components G06F11/00
• CPC Class Codes: H04N 1/00013 Reading apparatus
• CPC Class Codes: H04N 1/00031 Testing, i.e. determining the result of a trial H04N1/00029 takes precedence; using test signals for transmission mode changing H04N2201/33371
• CPC Class Codes: H04N 1/00053 out of service, i.e. outside of normal operation
• CPC Class Codes: H04N 1/00063 using at least a part of the apparatus itself, e.g. self-testing
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors
• CPC Class Codes: H04N 3/155 Control of the image-sensor operation, e.g. image processing within the image-sensor

Abstract

Apparatus and methods for testing an active pixel sensor ensure that a signal proportional to the quantity of light energy impinging on the active pixel sensor is reliably and accurately captured and made available for further on processing the rest of the APS system circuitry. The apparatus and method determines the capacitance of a photo-conversion device of the active pixel sensor. The apparatus and method determines that an active pixel sensor is functioning correctly. The apparatus and method determines the performance of an active pixel sensor. Where the performance of the active pixel sensor is a measure of linearity of the active pixel sensor and a connected chain of circuitry that process the signal converted by the photo-conversion device of the active pixel sensor.

Claims

1. A method for verifying operation of a group of at least one active pixel sensor within an array of active pixel sensors and of a chain of circuitry connected to each active pixel sensor for capturing an output signal from said active pixel sensor, whereby said chain of circuitry includes a column bus circuit and a signal conditioning and readout circuit, and whereby said method comprises the step of:

testing functionality of said group of active pixel sensors and the chain of circuitry connected to each active pixel sensor of the group of active pixel sensors by the steps of;

activating said group of active pixel sensors,

applying one of a group of voltage levels that vary incrementally from a first voltage level to charge a capacitance of a photo-conversion device of each active pixel sensor of the group of active pixel sensors to a first charging voltage level and sampling and holding said first charging voltage level from the capacitance of the photo-conversion device of each active pixel sensor of the group of active pixel sensors,

applying the first voltage level to charge the capacitance of the photo conversion device of each active pixel sensor of the group of active pixel sensors to a second charging voltage level,

sampling and holding a second charging voltage level from said capacitance of the photo-conversion device of each active pixel sensor of the group of active pixel sensors,

differentially comparing the first charging voltage level with the second charging voltage level to create a first difference voltage, whereby said first difference voltage indicates the functionality of each active pixel sensor of the group of active pixel sensors and the chain of circuitry connected to said active pixel sensor.