Sierra Video ADA-108 - Manual (Page 18)

SIERRA VIDEO
12
Circuit Description
Please refer to the Block Diagram above and the schematic in the following section when
reading the circuit description. The ADA-108 is a 1x8 composite video distribution
amplifier designed to work in an openGear 2 RU frame. The openGear frame can be
either a 10 slot or a 20 slot frame. In a ten slot frame all 8 outputs are available and the
input is a loop thru input, meaning that there two BNCs connected to the input of the DA.
One input BNC will receive the video from a source such as a VTR or a router and the
other BNC, loop-thru, can either be terminated in 75 ohms or connected to another
device with a cable. The other device must terminate the cable in 75 ohms or loop-thru to
another device that terminates in 75 ohms.
If the 20 slot openGear frame is used then only four outputs are available and the input
must be internally terminated in 75 ohms using the P1 jumper near the connector end of
the DA. This jumper should be set to ON for 20 slot frames.
The ADA-108 is DC coupled from input to output. There are no clamps or provisions to
AC couple the video through this DA. There is one front edge adjustment on the board for
setting the overall gain. This adjustment has a guaranteed range of 0dB, +/- 3dB. 0dB is
unity gain, which means that a 1V peak to peak input signal will produce a 1V peak to
peak signal out with input and output properly terminated in 75 ohms.
Refer to the Block Diagram for the video path and the schematic in the next section.
There are three stages to the VDA. First an input buffer stage, then a gain stage used for
adjusting the overall gain of the DA and lastly the output drivers.