Applications

SINGLE VIDEO CHANNEL

A typical application for a single video channel is shown in

Figure 9. The video signal is AC coupled to pin 6. The

LM2202 internally biases the video signal to 2.6 V

trast control is achieved by applying a 0V to 4V DC voltage

at pin 8. The amplifier’s gain is minimum (i.e., maximum sig-

nal attenuation) if pin 8 is at 0V and is maximum if pin 8 is at

4V. With pin 9 (drive control) at 0V, the amplifier has a maxi-

mum gain of 10.

For DC restoration, a clamp signal must be applied to the

clamp gate input (pin 14). The clamp signal should be logic

low (less than 0.8V) only during the back porch (black level

reference period) interval (see

Figure 2). The clamp gate in-

put is TTL compatible. Brightness control is provided by ap-

plying a 0V to 4V DC voltage at pin 19. For example, if pin 19

is biased at 1V then the video signal’s black level will be

clamped at 1V. A 510

Ω load resistor is connected from the

video output pin (pin 17) to ground. This resistor biases the

output stage of the amplifier. For power dissipation consider-

ations, the load resistor should not be much less than 510

Ω.

RGB VIDEO PREAMPLIFIER

Figure 10 shows an RGB video preamplifier circuit using

three LM2202s. Note that pins 1 and 2 of IC1 are connected

to pins 1 and 2 of IC2 and IC3 respectively. This allows IC1

to provide a master contrast control and optimum contrast

tracking. Adjusting the contrast voltage at pin 8 of IC1 will

vary the gain of all three video channels. Drive control input

(pin 9) of each LM2202 allows individual gain adjustment for

achieving white balance.

The black level of each video channel can be individually ad-

justed to the desired voltage by adjusting the voltage at pin

19. In a DC-coupled cathode drive application, adjusting the

voltage at pin 19 of each IC will provide cutoff adjustment. In

an AC-coupled cathode drive application, the video signal is

AC coupled and DC restored at the cathode. In such an ap-

plication, the video signal’s black level may be clamped to

the desired level by simply biasing pin 19 to the black level

voltage by using a voltage divider at pin 19.

DS012591-14

FIGURE 8. Simplified Schematic of the LM2202 Clamp Comparator Circuit

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