10

LT1195

S

APPLICATI

I FOR ATIO

Send Color Video Over Twisted-Pair

With an LT1195 it is possible to send and receive color

composite video signals more than 1000 feet on a low cost

twisted-pair. A bidirectional “video bus” consists of the

LT1195 op amp and the LT1187 video difference amplifier.

A pair of LT1195s at TRANSMIT 1, is used to generate

differential signals to drive the line which is back-termi-

nated in its characteristic impedance. The LT1187,

twisted-pair receiver, converts signals from differential to

single-ended. Topology of the LT1187 provides for cable

compensation at the amplifier’s feedback node as shown.

In this case, 1000 feet of twisted-pair is compensated with

1000pF and 50

Ω to boost the 3dB bandwidth of the

system from 750kHz to 4MHz. This bandwidth is adequate

to pass a 3.58MHz chrome subcarrier, and the 4.5MHz

sound subcarrier. Attenuation in the cable can be compen-

2, another pair of LT1195s serve the dual function to

provide cable termination via low output impedance, and

generate differential signals for TRANSMIT 2. Cable termi-

nation is made up of 15

Ω and 33Ω attentuator to reduce

the differential input signal to the LT1187. Maximum input

1.5MHz Square Wave Input and Equalized

Response Through 1000 Feet of Twisted-Pair

1.5MHz Square Wave Input and Unequalized

Response Through 1000 Feet of Twisted-Pair

Multiburst Pattern Passed Through

1000 Feet of Twisted-Pair

Vector Plot of Standard Color Burst Through

1000 Feet of Twisted-Pair

1195 A109

1195 A110

1195 A111

1195 A108