CHEETAH Hardware User’s Manual
Imperx, Inc.
Rev. 6.2
6421 Congress Ave.
7/7/2015
Boca Raton, FL 33487
+1 (561) 989-0006
12 of 152
1.3
CHEETAH SPECIFICATIONS
1.3.1 General Information
A CMOS camera is an electronic device for converting light into an electrical signal.
The camera contains a light sensitive element CMOS (Charge Coupled Device) where
an electronic representation of the image is formed. The CMOS image sensor consists
of a two dimensional array of sensitive elements – silicon photodiodes, also known as
pixels. The photons falling on the CMOS surface create photoelectrons within the
pixels, where 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 amount of electrons varies with the wavelength of
the incident light.
1.3.1.1 Rolling and Global Shutter Description
Cheetah C4080 and C2880 cameras support both global and rolling shutter readout
mode. In Global Shutter (GS) mode every pixel starts and stops integration at the same
time. This mode is excellent for clean capture of moving scenes without the need for a
mechanical shutter. When global shutter mode is used, all pixel data is stored in light
shielded regions within each pixel and held there until readout. (Figure 1.0a) In
Rolling Shutter (RS) mode each row of the image sensor is captured at a slightly
different time. (Figure 1.0b) This can cause distortions in the image, if an object is
moving very quickly and the integration time is short with respect to the frame readout
time. In rolling shutter mode, pixels in a row are cleared of charge, allowed to
integrate for the required exposure time and then the entire row is readout. The
resetting of each row ripples through the array and each row is exposed with a slight
time delay (equal to the line readout time) relative to the previous row. In RS mode,
the transistor within each pixel used to provide global shutter capability is used to
provide noise reduction.
