402-00005-00
Theory of Operation
2–14
Rev 02; February 8, 2002
2.5 CAMERA INTERFACE
The functional blocks that perform video input conditioning are: Input MUX, Gain and Offset, Low-Pass Filtering,
DC restoration, programmable ADC references, and ADC.
2.5.1 Input MUX
The input stage is a 2:1 analog video multiplexer (MUX) which allows two monochrome analog inputs from the
CAM0 and CAM1 connectors. The input is selected by software control. The timing is common to both inputs. Inde-
pendent timing is not available. Asynchronous inputs are not supported by the PCVisionplus. The timing and syn-
chronization settings apply to both inputs synchronously. Multiple monochrome cameras must be externally gen-
locked or driven by the PCVisionplus programmable timing. When using the sync stripper, the synchronization
signals must be input on the composite video signal, or on a separate (horizontal and vertical) sync signals on the
CAM0 or CAM1 connectors.
2.5.2 Gain
Data passes through a gain stage with a 2.1 gain setting. The 2.1 value, used with RS170 and CCIR video signals
provides the correct gain needed for the desired 1.5 Vpp sampling window of the ADC. Standard video signal ampli-
tude is 0.714 mV and 2.1 times 0.714 = 1.5 Volts. To achieve best performance, the video amplitude should fit the
sampling range of the ADC as closely as possible. As shown in Figure 2–13, there are several ways to accomplish
changing the video amplitude. The first step is always proper lighting at the video source, to achieve a good dynamic
range of the input video signal. The next option is to increase the incoming video amplitude (before the ADC). The
last resort should be adjusting the ADC sampling voltage range. The optimum range for the ADC used on the PCVi-
sionplus is 1.5 Volts peak-to-peak.
incomming
video signal
Input Gain Stage
Video signal
after gain
12-bit ADC
0.714 mV
1.5 Volts pp
1.5 Volts pp
2.1
Figure 2–13. Input Gain Stage
Incoming video is terminated into 75 ohm resistors, as Figure 2–14 illustrates. Camera output is specified as voltage
into a 75 ohm termination. The value at the video input connector (into 75 ohms) is half the measurable open circuit
value (no cable connected) at the camera output connector.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com