LM1207AN National Semiconductor, LM1207AN Datasheet - Page 12

• Manufacturer Part Number: LM1207AN
• Manufacturer: National Semiconductor

Specifications of LM1207AN

• Power Supply Requirement: Single
• Dual Supply Voltage (typ): Not RequiredV
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Mounting: Through Hole
• Lead Free Status / RoHS Status: Not Compliant

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Functional Description
Circuit Description
VIDEO AMPLIFIER INPUT STAGE
Figure 8 is a simplified schematic of one of the three video
amplifiers input stage along with the recommended external
components. The IC pin numbers are circled and all external
FIGURE 7. Timing Diagram
FIGURE 6. Block Diagram of LM1205A/LM1207A Video Amplifier
(Continued)
DS012866-15
12
components are shown outside the dashed line. The video
input is applied to pin 6 via a 10 µF coupling capacitor and a
30
through the input pin should an applied voltage surge rise
above V
LM1205A/LM1207A is not degraded by the 30
However, if EMI is a concern this resistor can be increased to
well over 100
come longer. DC bias to the input pin is provided by Q5 and
its associated input circuitry. Z1 is a 5.6V zener that gener-
ates the input bias voltage. Q1 is a buffer to the zener refer-
ence voltage with 5.0V generated at its emitter. Q3 and Q4
are connected as diodes. Q2 is close to being a diode in this
circuit. This configuration will give about 2.0V at the collector
of Q2. R2 and R3 are a voltage divider, setting the base of
Q5 to about 3.5V. This sets the emitter of Q5 to about 2.8V,
the bias voltage of the video input. This bias voltage is nec-
essary to assure that the entire video signal stays within the
active operating region of the LM1205A/LM1207A. The bias
voltage goes through R6, a 20k resistor, to the video input at
pin 6. R4 and R6 are of the same value and R4 is used to
compensate for beta variations of the transistors. Note that
the bias voltage passes through three diode drops (Q5, Q6,
resistor. The resistor is added to limit the current
CC
or drop below ground. The performance of the
where the rise and fall times will start to be-
DS012866-14
resistor.