Contact Image Sensor (CIS) Technology

Overview

The conventional document scanning with CCD requires a lens, which might cause image distortions, e.g. pin cushion distortion, especially for large sized documents. Scanning with CIS usually generates 1:1 images without any distortion.

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Scanning Methods

There are two types of scanning methods:

1)  Sheetfed type:  

The document sheet is fed  though the CIS module by a roller

2) Flatbed type:  

The document stays flat on a glass bed while the CIS module moves across the whole sheet.

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CIS Structure

CIS is composed of the following components:

 

1) Sensor Array and PCB

Sensors are aligned and mounted on a PCB with other passive components. Sensors’ characteristics defines the key features of the CIS, such as resolution, scanning speed, sensitivity, MTF, etc.

 

2) Light Source – to provide light for image scanning.

  • There are two types of light sources.

- Light Bar is for high speed CIS, it consists of array of LEDs evenly on a PCB.

- Light Guide is for low speed CIS, it has acrylic rod to convey uniform light from LED(s).

  • Numbers of light sources – Single-light is for low speed and low cost, while dual-light is good for high speed and wrinkled object scanning.

  • The LED wavelengths (or colors) supported: UV, R,G,B, NIR, White

- UV (ultra-Violet):         365 nm & 390 nm

- Visible:                         Blue, Green, Red

- NIR (Near Infrared):   880 nm & 940 nm

 

3) Lens Array – to focus the image for scanning

Sometime it is called Rod Lens or SLA (SELFOC Lens Array). There are single-row or dual-row types available, dual-row is for better collimation. Besides glass material with better quality, the Rod lens can be made of plastic material as well.

 

4) Cover Glass – The focus point of CIS is on the surface of the glass, which also serves as a protection.

 

5) Connector – The inputs/outputs of CIS. A cable is required to connect CIS to a system.

 

6) Housing – To house everything together, normally it is made of plastics, however, aluminum housing is also available for harsh environment.

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* CMOS supports customization from standard CIS modules according to customer’s requirements.