Cheetah Pregius Camera with GigE Vision
®
Interface – User Manual
August 27, 2019
Page
113
of
123
Rev 1.0
6 Image Sensor Technology
6.1 General Information
A CMOS camera is an electronic device for converting light into an electrical signal. The C2010,
C2410, C4010, C4110, C4410, C5410, and C6410 cameras contain the 2
nd
Generation Sony
Pregius CMOS (Complementary Metal-Oxide Semiconductor) image sensors with 3.45-micron
square pixels while the C3210 camera contains 3
rd
generation Sony Pregius CMOS image
sensors with 4.5-micron square pixels. The Pregius sensors have groundbreaking performance
with sensitivity better than many traditional Charge Coupled Device (CCD) image sensors. The
sensors have extremely low dark current and no visible fixed pattern noise, which has been
the bane of traditional CMOS image sensors.
The Sony CMOS sensor consists of a two-dimensional array of sensitive elements called silicon
photodiodes, also known as pixels. The photons falling on the CMOS surface create
photoelectrons within the pixels. The number of photoelectrons is linearly proportional to the
light level. Although the number of electrons collected in each pixel is linearly proportional to
the light level and exposure time, the number of electrons created in the pixel during any fixed
time period varies with the wavelength of the incident light.
When the camera reaches the desired exposure time, it shifts the charges from each pixel
photodiode onto a storage register within the pixel, reads out one row at a time digitizing
each pixel at 8, 10 or 12 bits as selected by the user. The user can also selectively output the
most-significant 8, 10 or 12 bits from each pixel with an impact to camera’s frame rate. Frame
time, or read-out time, is the time interval required for all the pixels to be read out of the
image sensor. In non-triggered or fast trigger mode, while reading out the image from the
storage registers within each pixel, the camera captures the next image. The exposure ends
just as the readout of the previous frame ends and the next frame begins.
Unlike traditional CCD image sensors, the Sony CMOS image sensor digitizes each pixel within
a row simultaneously. This allows for more settling time, which lowers the overall noise floor
and provides improved sensitivity. The low noise floor, combined with a reasonably large pixel
charge capacity and extremely low dark current, translates into a large dynamic range of
71 dB (12-bits) or 12 F-stops for 3.45-micron pixels and 77 dB (13-bits) or 13 F-Stops for
4.5-micron pixels.
The sensor allows you to apply up to 48 dB of gain to the image. The first 24 dB of gain is
analog gain and some improvement in noise performance may result. The camera applies the
last 24 dB of gain digitally, which affects both signal and noise equally. Digital Gain (up to
12 dB) can also be applied using the Digital Gain control.
