Contact Image Sensor (CIS) Technology
Imaging Sensor Overview: CCD Scanner vs CIS Scanner
CIS technology is commonly preferred for precise imaging. When using conventional Charged Couple Device (CCD) linear image sensors for scanning objects, an optical lens is required, which potentially leads to image distortions like pincushion distortion, especially when scanning larger documents. The effect is illustrated below:
In contrast, scanning with Contact Image Sensor (CIS) technology produces imaging with no optical distortion. CIS scanners are used when the scanner needs to deliver a precise scan at a 1:1 ratio. The use of a SELFOC Lens Array is one of the main reasons why CIS scans are so accurate.
The CIS advantages of greater clarity, greater affordability over the years, and low power consumption make the CIS scanner the commonly preferred imaging sensor.
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The illustration below shows how CIS performs contact scanning to achieve a clear image without optical distortion:
Contact Image Sensor Structure and Components
Contact image sensor modules are composed of the following components:
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Sensor Array and Printed Circuit Board
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Light source
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Lens array
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Cover glass
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Connector
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Housing
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Below is a cross section diagram of a CIS module for your reference:
Each component of the module is detailed below:
1) Sensor Array and Printed Circuit Board (PCB)
The imaging sensors are aligned and mounted on a PCB with other passive components.
Sensors’ characteristics define the key features of the contact image sensor.
These key features are: Resolution, scan width, scanning speed, sensitivity, MTF, etc.
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2) Light Source - Provides Illumination for Image Scanning
Contact image sensors have two types of illumination utilizing Light-emitting Diodes (LEDs):
​Light Bar: Well-suited for contact image sensors with higher scanning speed. A Light Bar consists of an array of LEDs evenly placed on a PCB.
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Light Guide: Well-suited for contact image sensors with lower scanning speed. A Light Guide has an acrylic rod to convey uniform illumination from LED(s).
The number of light sources may differ depending on the application:
Single-light: This illumination system is suitable for a low scan speed and low cost.
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Dual-light: This illumination system is suitable for high scan speed and scanning wrinkled objects.
The LED wavelengths (colors) suitable for use as light source:
Ultraviolet (UV), Red, Green, Blue, Near-Infrared (NIR), and White
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Ultraviolet wavelengths: 365 nm & 390 nm
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Visible Colors: Red, Green, Blue, White
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Near-Infrared wavelengths: 880 nm & 940 nm
3) Lens Array – An Important Aspect for Image Focus
This is sometimes called the Rod Lens or the SELFOC Lens Array (SLA).
There are single-row or dual-row types available.
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Dual-row is for better collimation. In addition to being constructed with glass material for better quality, the Rod lens can be made of plastic material as well to make the module more affordable.
4) Cover Glass
The focus point of the CIS is on the surface of the glass.
The contact image sensor's cover glass also serves as protection.
5) Connector
The CIS module's connector allows for the inputs/outputs of the CIS scanner.
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A camera link cable is required to connect the CIS module to a system to receive the scanned image.
6) Module Housing
The housing encapsulates everything together.
Normally the CIS module's housing is made of plastic.
However, for harsher environments, aluminum housing is also an option.
Scanning Methods for Contact Image Sensors
There are two types of scanning methods:
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1) Sheetfed Scanning:
The document sheet is fed though the CIS module by a roller.
2) Flatbed Scanning:
The document stays flat on a glass bed while the CIS scanner moves across the whole sheet.
CMOS Sensor Inc. is a trusted designer and manufacturer of contact image sensors (CIS) and CIS modules with over 25 years of engineering excellence.
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Frequently Asked Questions About Contact Image Sensors:
What kind of sensors do CIS modules use?
Contact Image Sensor modules utilize CMOS image sensors. This is why contact image sensors are also referred to as CMOS Image Sensors. The CMOS sensors are placed side-by-side to allow for a linear, close proximity scan. This sensor choice also allows for the usage of a SELFOC Lens Array instead of necessitating an optical lens that may result in optical lens distortions.
Can CIS be customized?
Yes, according to the many possibilities a project's requirements may necessitate. CIS customization is a possibility due to CMOS Sensor Inc's industry-leading expertise in designing CIS for a wide variety of applications.
CIS customization may include image resolution, scan width, illumination system, light source coloration which includes Red, Green, Blue, White, Near-infrared, and Ultraviolet, video output count, pixel rate, and more.
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