Ccd Vs. Cmos - Sensor Performance - Smartek Vision Giganetix GC Series User Manual

4.1.4 CCD vs. CMOS - Sensor Performance

Both CCD and CMOS technologies use the same principle, they transform light into electric charge and
convert it into electronic signals.
In a CMOS sensor, each pixel has its own charge-to-voltage conversion, and the sensor often also includes
amplifiers, noise correction, and digitization circuits, so that chip outputs are digital bits. In a CCD sensor,
each pixel's charge is transferred through a very limited number of output nodes to be converted to voltage,
buffered, and sent off chip as an analog signal.
This difference in readout techniques has major impact on sensor limitations and capabilities. Eight properties
describe sensor performance:
1. Speed - an attribute that favors CMOS over CCDs because most of the camera functions can be
placed on the image sensor.
2. Quantum Efficiency - the ratio between output signal and unit of input light energy. Rolling Shutter
CMOS sensors caught up massively within the past years and offer a similar performance.
3. Uniformity - is the consistency of response for different pixels under identical illumination conditions.
CMOS were traditionally much worse than CCDs, however new amplifiers have made the illuminated
uniformity of some CMOS close to that of CCDs.
4. Dynamic range - the ratio of a pixel's saturation level to its signal threshold. CCDs have the advantage
here.
5. Windowing - CMOS technology has the ability to read out a portion of the image sensor allowing
elevated frame rates for small regions of interest. CCDs generally have limited abilities in windowing.
6. Shuttering - the ability to start and stop exposure arbitrary, is superior in CCD devices. CMOS devices
require extra transistors in each pixel to provide uniform (Global) shuttering and achieve similar results
like CCD sensors.
7. Biasing and clocking - CMOS image sensors have a clear advantage in biasing and clocking, as
they work on single bias voltage and clock level.
8. Anti-blooming - is the ability to easily reduce localized overexposure without ruining the rest of the
image in the sensor. CMOS for the most part is immune to typical blooming. CCDs need higher
engineering skills and additional hardware to remove blooming.
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4 Image Acquisition
SMARTEK Vision Giganetix User Manual Version 2.1.4