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參數(shù)資料
| 型號： | LM1209 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | 運動控制電子 |
| 英文描述： | 130 MHz/100 MHz RGB Video Amplifier System with Blanking |
| 中文描述： | 130 MHz/100 MHz的RGB視頻信號放大器系統(tǒng)的沖裁 |
| 文件頁數(shù)： | 10/25頁 |
| 文件大小： | 434K |
| 代理商： | LM1209 |
Functional Description
(Continued)
The 0V to 4V drive control signal comes in on pin 18. Each
channel has its own drive section, therefore the crosstalk
compensation needed for the contrast control voltages is
not required for the drive control, thus no external pins for
the drive control. The drive attenuator features a full range
gain control over 40 dB. This gives no attenuation of the
video signal with a 4V control voltage. A 0.25V control volt-
age results in an attenuation of 40 dB.
The output of the drive attenuator stage goes to A2, the
amplifier in the DC restoration section. The video signal
goes to the non-inverting input of A2. The inverting side of
A2 goes to the output of gm1, the clamp comparator, and
the clamp capacitor at pin 8.
During the back porch period of the video signal a negative
going clamp pulse from pin 14 is applied to the clamp com-
parator, turning on the comparator. This period is where the
black level of the video signal at the output of the LM1208/
LM1209 is compared to the desired black level which is set
at pin 19. Figure 7 shows the timing of the clamp pulse
relative to the video signal. The clamp capacitor is charged
or discharged by gm1, generating the correction voltage
needed at the inverting input of A2 to set the video output to
the correct DC level. Removing the clamp pulse turns off
gm1 with the correction voltage being maintained by the
clamp capacitor during active video. Both the clamp pulse
and the blank pulse at pin 13 are TTL voltage levels.
There are actually two output sections,
b
A3 and
b
A4. Both
sections have been designed to be identical, except
b
A4
has more current drive capability. The output transistor
shown is part of
b
A4, but has been shown separately so
the user knows the configuration of the output stage.
b
A3
does not go to the outside world, it is used for feeding back
the video signal for DC restoration. Its output goes directly
to the inverting input of the clamp comparator via the volt-
age divider formed by the 500
X
and 4k resistors.
b
A4 will
be close to the same output as
b
A3 and will temperature
track due to the similar design of the two output stages.
However, the current at the output of
b
A4 will be ten times
the current at the output of
b
A3. To balance both outputs, a
load resistance of 390
X
needs to be connected from pin 20,
the green video output pin, to ground. Another input to
b
A4
is the blank pulse. When a negative going blank pulse is
applied to pin 13, the output of the LM1208/LM1209 is driv-
en to less than 0.1V above ground. Using the timing shown
in Figure 7 for the blank pulse, the output of the LM1208/
LM1209 will be less than 0.1V during the inactive portion of
the video signal. This is a ‘‘blacker than black’’ condition,
blanking the CRT at the cathodes. By using the blank func-
tion of the LM1208/LM1209 no grid blanking is necessary.
Note that the DC restoration is done by feeding back the
video signal from
b
A3, but blanking is done at
b
A4. By
using the two output stages, blanking can be done at the
CRT cathodes, and at the same time activate the DC resto-
ration loop.
V
CC1
goes to pins 3, 11 and 25 (seeFigure 1 ). These three
pins are all internally connected. For proper operation of the
LM1208/LM1209 it is necessary to connect
all
the V
CC1
pins to the input power to the PCB and bypass each pin with
a 0.1
m
F capacitor. V
CC2
is the input power at pins 22 and
23 for the three output stages. This is a separate power
input from V
CC1
, there are no internal connections between
the two different power inputs. There must be a connection
on the PCB between V
CC1
and V
CC2
. Pins 22 and 23 must
be bypassed by a parallel connection of a 10
m
F and 0.1
m
F
capacitors. The ground connections for the LM1208/
LM1209 are at pins 7, 21, and 24. All three ground pins are
internally connected, and these pins must also be connect-
ed externally to a good ground plane for proper operation of
the LM1208/LM1209.
http://www.national.com
10
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