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National Semiconductor - Monolithic Triple 180 MHz I2C CRT Pre-amp With Integrated Analog On Screen Display (OSD) Generator

Numéro de référence LM1253
Description Monolithic Triple 180 MHz I2C CRT Pre-amp With Integrated Analog On Screen Display (OSD) Generator
Fabricant National Semiconductor 
Logo National Semiconductor 





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LM1253 fiche technique
May 2000
LM1253A
Monolithic Triple 180 MHz I2C CRT Pre-amp With
Integrated Analog On Screen Display (OSD) Generator
General Description
The LM1253A pre-amp is an integrated high voltage triple
CRT pre-amp and Analog On Screen Display (OSD) genera-
tor. The IC is I2C controlled, and allows control of all the pa-
rameters necessary to setup and adjust the brightness and
contrast in the CRT display. In addition, it provides a pro-
grammable period vertical blanking pulse which is used to
blank the G1.
The LM1253A pre-amp is designed to work in cooperation
with the LM2453 driver, and provides a multiplexed video
signal (VideoPlex) interface to enable the DC clamp levels at
the cathode to be varied in order to set up the CRT bias and
to allow individual adjustment for brightness.
The Analog OSD has a selectable palette allowing a wide se-
lection of colors. The preset level of the OSD can be con-
trolled by I2C to suit different CRT displays. The OSD signal
is internally mixed with the video signal, before the gain sec-
tion, and thus gives excellent white tracking of the OSD with
the white color point setting of the video.
The Brightness settings are also mixed into the video signal
before the gain matching controls and consequently give ex-
cellent white color point tracking with variations in the Bright-
ness control. An active horizontal blanking signal is added to
the video at the output, giving excellent smear performance,
and preventing video content dependent DC bias offsets as
a result of high frequency over shoot.
The OSD horizontal sync and blanking signal is derived from
a positive going flyback pulse. The digital section provides
easy interfacing of this signal with the deflection circuits.
The vertical blanking signal is taken from the vertical sync
signal, and the blanking duration is programmable. This sys-
tem is highly integrated and requires a minimal number of
external components.
Black level clamping of the signal is carried out directly on
the AC coupled input signal into the high impedance pream-
plifier input, thus eliminating the need for additional black
level clamp capacitors.
The outputs are referenced to a DC level produced by the
LM1253A Pre-amp, and so are guaranteed to provide stable
DC operating levels within the system without the need for
additional external feedback components.
The IC is packaged in an industry standard wide body 28-
lead DIL molded plastic package.
Features
n 190 two-color ROM based Character Fonts
n 64 four-color ROM based Character Fonts
n Supports a programmable page size with up to 512
characters and line definition codes
n Support for 2 Display Windows (size of each window is
configurable)
n Programmable start position for each Display Window
n Programmable Resolutions: from 512 to 960 pixels per
line in 64 pixel increments
n Programmable Character Height, with automatic height
control with mode change
n Programmable Row Spacing between each display
character row
n Maximum Pixel clock of 92.2 MHz
n I2C compatible interface to controlling micro-controller
n Button boxes
n 180 MHz preamplifier with full video signal parametric
control
n VideoPlexinterface to the LM2453 driver
n OSD mixing with 64 out of 512 color mask
programmable selection
Intended Applications
n 1280 x 1024 Displays up to 75 Hz requiring OSD
capability
© 2000 National Semiconductor Corporation DS101265
www.national.com

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