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PDF LM1282 Data sheet ( Hoja de datos )
| Número de pieza | LM1282 | |
| Descripción | 110 MHz RGB Video Amplifier System with On Screen Display (OSD) | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM1282 (archivo pdf) en la parte inferior de esta página. Total 14 Páginas | ||
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June 1998
LM1282
110 MHz RGB Video Amplifier System with On Screen
Display (OSD)
General Description
The LM1282 is a full feature video amplifier with OSD inputs,
all within a 28-pin package. This part is intended for use in
monitors with resolutions up to 1280 x 1024. The video sec-
tion of the LM1282 features three matched video amplifiers
with blanking. All of the video amplifier adjustments feature
high input impedance 0V to 4V DC controls, providing easy
interfacing to bus controlled alignment systems. The OSD
section features three TTL inputs and a DC contrast control.
The switching between the OSD and video section is con-
trolled by a single TTL input. Although the OSD signals are
TTL inputs, these signals are internally processed to match
the OSD logic low level to the video black level. When ad-
justing the drive controls for color balance of the video sig-
nal, the color balance of the OSD display will track these
color adjustments. The LM1282 also features an internal
spot killer circuit to protect the CRT when the monitor is
turned off. For applications without OSD insertion please re-
fer to the LM1205 or LM1208 data sheets.
Features
n Three wideband video amplifiers 110 MHz @ −3 dB
(4 VPP output)
n TTL OSD inputs, 50 MHz bandwidth
n On chip blanking, outputs under 0.1 V when blanked
n High speed Video/OSD switch
n Independent drive control for each channel for color
balance
n 0V to 4V, high impedance DC contrast control with over
40 dB range
n 0V to 4V, high impedance DC drive control (0 dB to
−12 dB range)
n 0V to 4V, high impedance DC OSD contrast control with
over 40 dB range
n Capable of 7 VPP output swing (slight reduction in
bandwidth)
n Output stage directly drives most hybrid or discrete CRT
drivers
Applications
n High resolution RGB CRT monitors requiring OSD
capability
Block and Connection Diagram
FIGURE 1. Order Number LM1282N
See NS Package Number N28B
© 1998 National Semiconductor Corporation DS012519
DS012519-1
www.national.com
1 page  
Typical Performance Characteristics VCC = 12V, TA = 25˚C unless otherwise specified (Continued)
LM1282 Crosstalk vs Frequency
LM1282 Contrast vs Frequency
DS012519-4
LM1282 Drive vs Frequency
DS012519-5
DS012519-6
5 www.national.com
5 Page 
Pin Descriptions (Continued)
Pin Pin
No. Name
18 Blue Video Out
20 Green Video Out
23 Red Video Out
Schematic
Description
Video output. For proper black level the output must drive
390Ω impedance.
22 VCC2
25 RGB Cutoff Adjust
Power supply pin for the output stage. There are no internal
connections to VCC1.
Sets the black level of the video outputs to all three
channels. Range is 0V to 4V. Minimum black level is limited
to about 300 mV.
Functional Description
Figure 1 on the front page shows the block diagram of the
LM1282 along with the pinout of the IC. Each channel re-
ceives both a video signal and an OSD signal at its input am-
plifier (−A1). The Video/OSD Switch signal also goes to the
input amplifiers, controlling whether the video or the OSD
signal passes through the LM1282. Both the OSD inputs and
the Video/OSD Switch accept standard TTL signals. If video
is selected then a TTL low is applied to pin 4, for OSD a TTL
high needs to be applied. When the OSD feature is not used,
then pin 4 needs to be connected to ground via a 47k resis-
tor. Although the OSD input signal is a TTL signal, the input
amplifier processes this signal to match the video levels. A
TTL high signal will be at the video white level and a TTL low
signal will typically be within 100 mV of the video black level.
Note that by using the LM1282 the monitor designer con-
nects the OSD input signals directly to the IC with NO signal
processing.
DC restoration is performed on the video inputs to the
LM1282. Remember video inputs are always AC coupled to
the video pre-amp. There is no DC standard for the video in-
put, therefore AC coupling the video inputs is necessary for
proper operation of the monitor. A minimum capacitance of 1
µF is recommended at the video input pins. The preferred
value is 10 µF. Part of the signal processing of the TTL OSD
inputs is matching the black level of the OSD signal (TTL
low) to the black level of the video signal. With AC coupling
of the video inputs, DC restoration must be done at the input
to perform the black level matching.
The next stage in the LM1282 is the Contrast Attenuation.
Both the video and OSD contrast controls go to this stage.
For easy interfacing to 5V DACs all control inputs, including
these two controls, use a 0V to 4V range. Both contrast con-
trols give no attenuation at 4V and full attenuation (over −50
dB) at 0V. The video and OSD contrast adjustments are
completely independent of each other, allowing the user to
set the desired contrast of the OSD window without affecting
the video portion of the display. There is only one output from
this section, any adjustments on the signal path beyond the
contrast stage affects both the video signal and the OSD sig-
nal.
Following the Contrast Attenuation block is the Drive Attenu-
ation. By having the Drive Attenuation past the contrast
stage, any adjustment made on the video signal will equally
affect the OSD signal. This configuration simplifies the white
level adjustment. When the white level of the video is ad-
justed then the OSD white level is automatically set. The
only OSD adjustment necessary when using the LM1282 is
the OSD contrast. Note that when performing the white level
adjustments the video portion of the display must be used,
because there are minor variations between the OSD levels
and the video levels.
The output stage is the −A2 amplifier. This stage is similar to
the LM1205 output stage, where the video output can be
blanked to a level below the video black level. A blacker than
black output during blanking provides the capability to blank
at the cathodes of the CRT. This eliminates the need for us-
ing high voltage transistors at G1 of the CRT to perform the
blanking function. When the outputs are blanked the
LM1282 can still DC restore the video output signal by using
the Clamp Gate. There is an internal feedback stage that
does the DC restoration. In order to maintain the correct
video levels based on this feedback loop, the video output of
the LM1282 must be terminated with a 390Ω impedance.
The required correction voltage for DC restoration is stored
on the clamp cap. A value of 0.1 µF is recommended for the
clamp cap. If the cap value is too small then there will be a tilt
(shift) in the DC level of the video output during the horizon-
tal scan. If the cap value is too large, then the DC restoration
circuit may not be able to maintain the proper DC level of the
video signal. Since DC restoration is also done at the video
inputs, larger clamp cap values will be less of a problem with
the LM1282 than with most other video preamps. The refer-
ence level for the DC restoration circuit is set at the RGB
Cutoff Adjust pin (pin 25). Most monitor applications AC
11 www.national.com
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet LM1282.PDF ] | |
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