Design of a CMOS Image Sensor with Bi-Directional Gamma-Corrected Digital-Correlated Double Sampling

Area of Science:

• Electrical Engineering
• Image Sensor Technology
• Semiconductor Devices

Background:

• Analog correlated double sampling (CDS) in CMOS image sensors (CIS) for gamma correction is susceptible to imperfections.
• Existing methods for in-circuit gamma correction face limitations due to analog circuit vulnerabilities.

Purpose of the Study:

• To develop a robust in-circuit bi-directional gamma correction technique for CMOS image sensors.
• To address the limitations of analog CDS by proposing a digital-CDS approach.

Main Methods:

• Implementation of a 640x480 CMOS image sensor (CIS) featuring a novel digital-correlated double sampling (CDS) structure.
• Utilizing a hold-and-go counter for digital-CDS to enable bi-directional gamma correction.
• Integration of a global log-exponential counter and configurable column reset counter for 10-bit resolution.

Main Results:

• Achieved a maximum Signal-to-Noise Ratio (SNR) improvement of 10.41% using the proposed bi-directional gamma-corrected digital-CDS.
• The sensor demonstrated a 10-bit resolution with 8/9-bit configurable column reset counters.
• Fabricated on a 0.11 μm CIS process with a chip area of 5.9 mm × 5.24 mm.

Conclusions:

• The proposed digital-CDS method effectively enables robust bi-directional gamma correction in CIS.
• This advancement leads to significant SNR improvements in image sensor performance.
• The developed sensor offers high resolution and low power consumption (6.3 mW at 16.6 fps).