CHEETAH Hardware User’s Manual
Imperx, Inc.
Rev 1.7
6421 Congress Ave.
8/26/2016
Boca Raton, FL 33487
+1 (561) 989-0006
34 of 121
2.2
FRAME TIME CONTROL
2.2.1 Internal Line and Frame Time Control
The camera speed (frame rate) depends on the CMOS “read-out” time – the time
necessary to read all the pixels out of the CMOS imager. The frame rate can be
calculated using the following Formula 1.1:
Frame rate [fps] = 1 / read-out time [sec]
(1.1)
2.2.1.1 Pixel Clock Line Rate Control
The user can program the camera to run slower than the fastest speed preserving the
camera full resolution by extending the camera frame time (the time required to read
the entire frame out of the CMOS imager). The time to readout a line is controlled
by the Pixel Clock Rate control in the Acquisition Sub-Menu. Since the image
sensor readout speed exceeds the Camera Link interface output rate, the Pixel Clock
Rate control is used to match the camera output rate to the frame grabber capture
rate.
The Pixel Clock should always be adjusted to the maximum rate possible without the
frame grabber missing or skipping data. In this way, the dark current generated
within the pixel and the dark current noise is minimized.
2.2.1.2 Programmable Frame Time Control
Once the Pixel Clock has been adjusted to minimize the line readout time, the user
can increase the frame time by using the Programmable Frame Time feature. When
programmable frame time control is enabled, the frame is readout and then the
camera idles inserting a vertical blanking period at the end of the frame readout to
provide the desired frame rate.
In this way, the user can reduce the camera output frame rate to match the
application requirements. The frame time can be reduced to about ~1 second with a
precision of 1 micro-second. The programmable frame time control can be used to
support exposure times longer than the time necessary to readout the image sensor.
2.2.1.3 Zero-Row Overhead (ROT) Control
A Row-Overhead time (ROT) control is provided and the control is called: “Zero-
Row Overhead Time” (Zero-ROT). Disabling Zero-ROT adds one micro-second of
blanking time at the end of each row to further reduce the line rate. Zero-ROT
should only be used as a last resort and only when decreasing Pixel Clock line rate
control to the minimum value still results in frame grabber overruns. Zero-ROT must
