Image Sensors Explained: How CCD and CMOS Sensors works? CCD vs CMOS

In this video, modern-day image sensors like, CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) have been briefly explained. And the comparison between CCD and CMOS sensor is carried out in various aspects.

Both CCD and CMOS sensors consist of an array of tiny photosites (pixels) which converts incoming light into the charge.

The following steps are common in both CCD and CMOS sensors, but the sequence in which it is carried out might differ in two sensors.

1. Conversion of incoming light into the charge
2. Charge Accumulation
3. Charge Transfer
4. Charge to Voltage Conversion
5. Voltage amplification

CCD Sensor:

In case of CCD Sensor, the incoming light is converted into charge, and then charge to voltage conversion is carried out, outside the sensor area.
Most CCD sensor has a single charge to voltage conversion circuit and single amplifier. So, charge from each pixel is transferred to the next row (or next column) and eventually to the shift register.
In shift register, the charge is transferred one by one and then it is converted into the voltage.

CMOS sensor:

In case of CMOS sensor, the charge to voltage conversion and voltage amplification is carried out in the pixel itself. So, each pixel has its own charge to voltage converter circuit and voltage amplifier circuit. Such CMOS sensor pixels (which contains amplifier) are known as the active pixel sensor.
In case of CMOS sensor, the reading of the pixel voltage is carried out in line by line fashion.

Comparision of CCD and CMOS sensors:

1. System integration:
In case of CMOS sensor as the peripheral circuit is also integrated into the sensor chip itself. While in case of CCD sensor, for peripheral components, the different chip is required.

2. Power Consumption:
CMOS requires less power than CCD Sensors.

3. Processing Speed:
CMOS sensor is much faster than CCD sensors.

4. Noise and sensitivity
CCD sensor has less noise than CMOS sensor and also it has better sensitivity. But nowadays using different techniques like microlens on each pixel of CMOS sensor, the sensitivity can be increased.

Time stamps for the different topics are given below:

0:34 Overview of CCD and CMOS Sensors

1:36 How CCD Works?

2:53 How CMOS sensor Works?

4:01 Comparision between CCD and CMOS Sensors

4:11 Comparision in terms of the system integration

4:51 Comparision in terms of Power Consumption

5:37 Comparision in terms of the Processing Speed

6:33 Comparison in terms of the Noise and Sensitivity

7:25 Comparision in terms of the image distortion

This video will be helpful to all in understanding the CCD and CMOS image sensors.

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