Cheetah Pregius Camera with 10 GigE Vision Interface – User Manual
October 8, 2020
Page
147
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170
Rev 1.0
Image Sensor Technology
General Information
A CMOS camera is an electronic device for converting light into an electrical signal. The C4440,
C5440, and C6440 cameras contain Sony Pregius CMOS (Complementary Metal-Oxide
Semiconductor) image sensors with 3.45-micron square pixels. 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 10 or 12 bits. The user can 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.
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.
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. Additional digital gain (up to 12 dB)
can also be applied using the Digital Gain control.
