Image Sensor – Working & Its Applications

The camera’s image sensor is in charge of turning light and the color spectrum into electrical impulses that the camera can then translate into zeroes and ones. They mimic the transduction process that a human performs biologically. Where transduction simply means converting one form of energy into another form.

There are mainly two types of an image sensor

CCD (Charged-Coupled Device) Image Sensor

CCD consists of millions of pixels, these pixels will convert the incoming light into a charge which is then gets stored in the pixels as shown in the below image.

The charge is then transferred using the horizontal shift register to the vertical shift register once it has been gathered by the pixels. In this shift register, each charge is now converted into the voltage one by one and amplified also using the charge to voltage converter and amplifier.

After the vertical shift register is empty the next row of stored charge is shifted in the vertical shift register and then that row of charge is converted into voltage and further amplified. This process is repeated for every row. Finally, the amplified voltage which is an analog signal is converted into digital form using an Analog to Digital converter.

In CMOS, fabrication technology is very similar to the fabrication technology of the integrated circuits therefore many peripheral circuits can be integrated on a single chip.
The basic function of storing the charge is similar to the CCD but as the peripheral circuits can be integrated due to modern fabrication technologies, each pixel has its charge to voltage converter and an amplifier right next to it.

The working structure of the CMOS image sensor is shown in the above image
As the charge to voltage conversion and amplification is done in the pixel itself it has a much higher processing speed than the CCD image sensor.
The voltage produced by each pixel is measured line by line, therefore the pixel select switch is used to activate the first line of the pixel and link it to the column line. The data of every pixel can then be read by turning on the column select switch one by one, and the process is repeated for the remaining lines.

Both analog and digital electronic imaging systems, such as digital cameras, camera modules, camera phones, optical mouse devices, medical imaging equipment, and night vision equipment including thermal imaging devices, radar, sonar, and other devices, use image sensors.
The frame rate that cameras used to enable industrial automation can now capture has improved thanks to new image sensor technology. The use of these cameras in automation applications like inspection is growing due to the improved image quality brought on by the increased frame rate.
Image sensors are being used to automate tasks that would have once been allocated to human workers. For example, simple assembly tasks.
The importance of security applications has significantly increased due to numerous terrorist attacks worldwide. This area also greatly benefits from the achievements in the image sensors field. Today we can meet the cameras not only in military applications but also in commercial and civilian applications.
Biometric personal identification is strongly related to security and it refers to “identifying an individual based on his or her distinguishing physiological and/or behavioral characteristics. Almost all biometric characteristics, shown in Figure 10, require some kind of sense. Usually, conventional image sensors with external hardware or software image processing are used.