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ACTIVE PIXEL SENSOR

ACTIVE PIXEL SENSOR. TECHNOLOGY. HEMAKUMAR.B. 1D or 2D array of photosensors can record optical images projected onto it by lens system. Individual photosensor in an imaging array is called pixel ( pict ure el ement). High image resolution requires small pixels.

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ACTIVE PIXEL SENSOR

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  1. ACTIVE PIXEL SENSOR TECHNOLOGY HEMAKUMAR.B

  2. 1D or 2D array of photosensors can record opticalimages projected onto it by lens system. • Individual photosensor in an imaging array is calledpixel (picture element). • High image resolution requires small pixels.

  3. Two strategies for pixel operation: • Continuous-time mode Conversion of photogenerated charge into steady-state photocurrent • Integration mode Collection of photogenerated charge on capacitor until readout, followed by reset

  4. Some preliminaries...... • FILL FACTOR • CONVERSION GAIN • SENSITIVITY • FRAME RATE • FIXED PATTERN NOISE • BLOOMING

  5. Image Sensors: • Charge Coupled Devices (CCD’s) • Complementary Metal Oxide Semiconductors (CMOS) • * Passive Pixel Sensor (PPS) • * Active Pixel Sensor (APS) • Photogate Active Pixel Sensor (APS + CCD)

  6. CCD Image Sensors  A CCD is a dynamic analog (charge) shift register implemented using closely spaced MOS capacitors clocked using 2, 3, or 4 phase clocks -- capacitors operate in deep depletion regime when clock is high  Charge transfer (from one capacitor to the next) must occur at high enough rate to avoid corruption by leakage, but slow enough to ensure high charge transfer efficiency

  7. Advantages of CCDs : • optimized photodetectors • very low noise • very low fixed pattern noise

  8. Disadvantages of CCDs : • cannot integrate other analog or digital circuits. • highly nonprogrammable. • high power. • limited frame rate.

  9. CCD camera built for a mission to Pluto

  10. CMOS IMAGE SENSORS PPS APS

  11. APS

  12. Each pixel in an APS consists of a photosensitive part (photodiode) and a signal conditioning part Transistors amplify the current produced by the photodiode and connect it to a common readout structure For each pixel there is a sensor containing typically three transistors. The conversion of light energy (photons) to a voltage or current (electrons) is realised within the sensor.

  13. Can be produced in standard CMOS technology. • Pixels offer random access. • Pixel readout is non destructive & is repeatable. • Exposure time can be programmed electronically • Dissipates less electric power, Less blooming. • More robust under Xrays ADVANTAGES OF APS

  14. DISADVANTAGES: • Reduced optical fill factor. • Increased offset noise. • Impossible to perform correlated double sampling for noise reduction.

  15. APPLICATIONS Toys PC cameras space applications medical applications high resolution digital cameras

  16. & high speed Digital still cameras

  17. SUMMARY • Pixel & two stragedies for pixel operation. • Types of Image sensors. • CCD image sensors, its merits & demerits. • CMOS image sensors, its merits & demerits. • Applications of APS.

  18. THANK YOU

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