Cmos image sensors

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1. CMOS Image Sensors Presented by Md.Abdur Rahman ID: 1402EEE00019 2 nd Batch Dept of EEE ( MIU)

2. Content What is CMOS sensor . Types of CMOS  Sensors. How CMOS Sensors work. Operation of CMOS Sensors. Advantage of CMOSS.

3. What is CMOS sensor A CMOS (complementary metal oxide semiconductor ) sensor is an electronic chip that converts photons   to  electrons for digital processing. CMOS sensors are used to create images in digital cameras, digital video cameras and digital CCTV cameras. CMOS can also be found in astronomical telescopes, scanners and  barcode  readers. The optical technology is used in  machine vision  for robots, in optical character recognition (OCR), in the processing of satellite photographs and in the enhancement of radar images, especially for meteorology.

4. Types of CMOS Sensors CMOS Humidity & Temperature Sensors. 3D Imaging Sensor. CMOS X-ray Detectors. CMOS Micro hotplates. CMOS sensor for fluid flow.

5. How CMOS Sensors work CMOS SENSORS A typical CMOS is an integrated circuit with an array of pixel sensors. In contrast to CCD, each pixel sensor in CMOS sensors contains its own light sensor, an amplifier and a pixel select switch. An analog -to-digital converter and other components critical to the operation of the pixel sensors are located on the CMOS sensor.

6. The CMOS sensor contains four main parts: # The colour filters, # Pixel array, # Digital controller, and the # Analog to digital convertor.

7. •  Color Filter Color filter is the same as was described in CCD based imager.   •  Pixel Array As in the case of CCD, function of the pixel array is to capture the intensity of the light passing through. Each pixel sensor converts the sensitivity of the incoming light to the voltage signal which is then fed to ADC for further processing             There are two types of architectures of Pixel sensors: 1. Passive Pixel Sensor ( PPS) 2. Active Pixel Sensors (APS).

8. In Passive Pixel sensors, only one photo-detector (without any local amplifier) per pixel is used In Active Pixel sensors, 3-4 transistors per pixel are used . Passive Pixel sensors have smaller pixels and large fill factor but they are slow and have low SNR. On the other hand, active pixel sensors are fast, have good SNRs but larger pixels and low fill factor.

9. •  ADC The ADC takes the analog voltage signals from the pixel sensor array and converts them into a digital signal.   • Digital Controller The digital controller governs the functioning of the CMOS sensor; it controls the pixel array, ensures synchronism between all pixels, etc.

10. Operation of CMOS Sensors a) Pixel sensor acts like a charge bucket; accumulates electron charges the same way as water bucket stores water b)  Charge is converted to voltage & amplified at the pixel. c) Individual CMOS microwire  carry voltage from one pixel at a time, controlled by the pixel select switch

11. Advantage of CMOSS High frame rate. High resolution. Low power consumption. Improved noise performance. Improved quantum efficiency. Strong dynamic performance. Good price/performance ratio.

12. Thank you