Video Inputs Electrical Specifications
The VIDEO connector has 4 identical Video Inputs. Each port has two pins named VID_INxx and VRN_INxx respectively, where xx is a number ranging from 1 to 4. The "hot conductor" of the transmission line transporting the video signal xx has to be connected to the VID_INxx pin, while the "cold conductor" of the transmission line has to be connected to the corresponding VRN_INxx pin. If the transmission line is a coaxial line, the "hot conductor" is the inner conductor, and the "cold conductor" is the outer conductor.
A switchable 75Ω termination resistor is inserted directly across VID_INxx and VRN_INxx. The termination resistor can be disconnected by a DIP switch.
The factory settings of the termination resistor DIP switch are ON.
The video signal flows through a common-mode choke which attenuates any common-mode noise present on the video signal. The VRN_INxx pin is connected to the analog GND through one winding of the common-mode choke. The VID_INxx pin is connected to the second winding.
The filtered video signal (slightly attenuated by the 1kΩ/10kΩ resistor network) is AC-coupled to a video input of the video decoder. The 1 kΩ resistor protects the video decoder input against excessive currents in case of abnormal signal levels applied on the Video inputs.
The filtered video signal is also AC-coupled to an input of the video multiplexer circuit.
Video Input circuit
Video inputs - DC characteristics
Parameter |
Min |
Typ. |
Max |
Units |
Input voltage range - Absolute max rating |
-0.55 |
|
+2.2 |
V |
Input impedance - Terminator OFF |
|
11 |
|
kΩ |
Input impedance - Terminator ON |
|
75 |
|
Ω |
For a correct operation of the video decoder, the video signal must satisfy all following electrical requirements.
Video signal electrical requirements
Parameter |
Min |
Typ. |
Max |
Units |
Overall peak-to-peak amplitude |
0.5 |
1.0 |
1.5 |
V |
Sync amplitude |
150 |
300 |
400 |
mV |
Rise/Fall time of sync edges |
50 |
|
300 |
ns |
Lower video signal amplitudes are not recommended.
The signal attenuation induced by the 1kΩ/10kΩ resistor network circuit is compensated by the front-end amplifier in the input stage of the video decoder.