LT1195 UUWUAPPLICATIO S I FOR ATIOSend Color Video Over Twisted-Pair1.5MHz Square Wave Input and EqualizedResponse Through 1000 Feet of 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 50Ω to boost the 3dB bandwidth of the 1195 A109 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- Multiburst Pattern Passed Through1000 Feet of Twisted-Pair sated by lowering the gain set resistor RG. At TRANSMIT 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 15Ω and 33Ω attentuators to reduce the differential input signal to the LT1187. Maximum input signal for the LT1187 is 760mVP-P. 1.5MHz Square Wave Input and UnequalizedResponse Through 1000 Feet of Twisted-Pair 1195 A110 Vector Plot of Standard Color Burst Through1000 Feet of Twisted-Pair 1195 A108 1195 A111 1195fa 10
