Additional Applications of the LM1203

Figure 9 shows how the LM1203 can be set up as a video

buffer which could be used in low cost video switcher appli-

cations Pin 14 is tied high to turn off the clamp compara-

tors The comparator input pins should be grounded as

shown Sync tip (black level if sync is not included) clamping

is provided by diodes at the amplifier inputs Note that the

clamp cap pins are tied to the Pin 11 24V reference This

was done along with the choice of 200X for the drive pin

resistor to establish an optimum DC output voltage The

contrast control (Pin 12) will provide the necessary gain or

attenuation required for channel balancing Changing the

contrast control setting will cause minor DC shifts at the

amplifier output which will not be objectionable as the out-

put is AC coupled to the load The dual NPNPNP emitter

follower will provide a low impedance output drive to the AC

coupled 75X output impedance setting resistor The dual

500 mF capacitors will set the low frequency response to

approximately 4 Hz

TLH9178 – 9

FIGURE 9 RGB Video Buffer with Diode Sync Tip Clamps and 75X Cable Driver

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