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PDF LM1208N Data sheet ( Hoja de datos )

Número de pieza LM1208N
Descripción 130 MHz/85 MHz RGB Video Amplifier System with Blanking
Fabricantes National Semiconductor 
Logotipo National Semiconductor Logotipo



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OBSOLETE
October 2001
LM1208
130 MHz/85 MHz RGB Video Amplifier System with
Blanking
General Description
The LM1208 is a very high frequency video amplifier system
intended for use in high resolution RGB monitor applications.
In addition to the three matched video amplifiers, the
LM1208 contains three gated single ended input black level
clamp comparators for brightness control, three matched DC
controlled attenuators for contrast control, and three DC
controlled sub-contrast attenuators providing independent
full range gain control in each channel for wide range white
balance. All DC control inputs offer high input impedance
and an operation range from 0V to 4V for easy interface to
bus controlled alignment systems. The LM1208 also con-
tains a blanking circuit which clamps the video output volt-
age during blanking to within 0.1V above ground. This fea-
ture provides blanking capability at the cathodes of the CRT.
A spot killer is provided for CRT phosphor protection during
power-down.
Features
n Three wideband video amplifiers 130 MHz (LM1208) @
−3 dB (4 VPP output)
n Matched (±0.1 dB or 1.2%) attenuators for contrast
control
n ESD susceptibility above 3 kV
n Three externally gated single ended input comparators
for cutoff and brightness control
n 0V to 4V, high input impedance DC contrast control
(>40 dB range)
n 0V to 4V, high input impedance DC full range gain
control (Drive) for each video channel (> 40 dB range)
n Spot killer, blanks output when VCC < 10.6V
n Capable of 7 VPP output swing (slight reduction in
bandwidth)
n Output stage blanking
n Output stage directly drives most hybrid or discrete CRT
drivers
Applications
n High resolution RGB CRT monitors
n Video AGC amplifiers
n Wideband amplifiers with gain and DC offset controls
n Interface amplifiers for LCD or CCD systems
Block and Connection Diagram
DS100083-1
FIGURE 1.
Order Number LM1208 See NS Package Number N28B
© 2001 National Semiconductor Corporation DS100083
www.national.com

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LM1208N pdf
Typical Performance Characteristics VCC = 12V, TA = 25˚C unless otherwise specified (Continued)
LM1208 Crosstalk vs Frequency
LM1208 Contrast vs Frequency
DS100083-4
LM1208 Drive vs Frequency
DS100083-5
DS100083-6
5
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LM1208N arduino
Functional Description (Continued)
FIGURE 6. Block Diagram of LM1208 Video Amplifier
DS100083-11
FIGURE 7. Timing Diagram
DS100083-12
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
components are shown outside the dashed line. The video
input is applied to pin 6 via a 10 µF coupling capacitor and a
30resistor. The resistor is added to limit the current
through the input pin should an applied voltage surge rise
above VCC or drop below ground. The performance of the
LM1208 is not degraded by the 30resistor. However, if EMI
is a concern this resistor can be increased to well over 100
where the rise and fall times will start to become longer. DC
bias to the input pin is provided by Q5 and its associated
input circuitry. Z1 is a 5.6V zener that generates the input
bias voltage. Q1 is a buffer to the zener reference 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 necessary to
assure that the entire video signal stays within the active
operating region of the LM1208. 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, and Q7) before
setting the voltage across R9. Q2, Q3, and Q4 also provide
three diode drops to the bias voltage at the base of Q5,
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