LM1205N National Semiconductor, LM1205N Datasheet - Page 8

• Manufacturer Part Number: LM1205N
• Description: IC VIDEO AMP 130MHZ RGB 28DIP
• Manufacturer: National Semiconductor

Specifications of LM1205N

• Applications: General Purpose
• Number Of Circuits: 3
• -3db Bandwidth: 130MHz
• Current - Supply: 90mA
• Current - Output / Channel: 28mA
• Voltage - Supply, Single/dual (±): 10.8 V ~ 13.2 V
• Mounting Type: Through Hole
• Package / Case: 28-DIP (0.600", 15.24mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *LM1205N

Figure 5 shows the block diagram of a typical analog RGB
Figure 5 block labeled ‘‘VIDEO AMPLIFICATION WITH
Figure 6 is a detailed block diagram of the green channel of
Applications Information
color monitor The RGB monitor is used with CAD CAM
work stations PC’s arcade games and in a wide range of
other applications that benefit from the use of color display
terminals The RGB color monitor characteristics may differ
in such ways as sweep rates screen size CRT color trio
spacing (dot pitch) or in video amplifier bandwidths but will
still be generally configured as shown in Figure 5 Separate
horizontal and vertical sync signals may be required or they
may be contained in the green video input signal The video
input signals are usually supplied by coax cable which is
terminated into 75
coupled to the video amplifiers These input signals are ap-
proximately 1V peak to peak in amplitude and at the input of
the high voltage video section approximately 5V peak to
peak At the cathode of the CRT the video signals can be as
high as 60V peak to peak One important requirement of the
three video amplifiers is that they match and track each
other over the contrast and brightness control range The
GAIN AND DC CONTROL’’ describes the function of the
LM1205 which contains the three matched video amplifiers
contrast control and brightness control The LM1205 also
provides the capability to blank at the cathode of the CRT
Functional Description
the LM1205 along with the recommended external compo-
nents The IC pin numbers are circled and all external com-
ponents are shown outside the dashed line The other two
video channels are identical to the green channel only the
numbers to the pins unique to each channel are different
The input video is normally terminated into 75
at the monitor input and internally AC
FIGURE 5 Typical RGB Color Monitor Block Diagram
(Continued)
The termi-
8
nation resistor depends on the impedance of the coax cable
being used 75
in video applications The video signal is AC coupled
through a 10
standard for the DC level of a video signal therefore the
signal must be AC coupled to the LM1205 Internal to the
LM1205 is a 2 8V reference giving the input video an offset
voltage of 2 8V This voltage was selected to give the input
video enough DC offset to guarantee that the lowest voltage
of the video signal at pin 6 is far enough above ground to
keep the LM1205 in the active region The 200
the input is for ESD protection and for current limiting during
any voltage surge that may occur at the input driving pin 6
above V
this circuit description an inverting amplifier is shown with a
‘‘
output of
sections
The contrast and drive control sections are virtually identi-
cal Both sections take a 0V to 4V input voltage 4V giving
the maximum gain for either the contrast or the drive This is
a high impedance input allowing for an easy interface to 5V
DACs One may also use 100k potentiometers with no deg-
radation in performance The contrast control section is
common to all three channels It converts the input voltage
at pin 12 to a couple of internal DC voltages that control the
gain of the contrast attenuator Referring to the Attenuation
vs Contrast Voltage under typical performance characteris-
tics note that a 4V control voltage results in no attenuation
of the video signal A 0 5V control voltage results in an at-
tenuation of 35 dB Again note that these internal control
voltages are common to all three channels To minimize
crosstalk these voltages go to pins 1 and 2 Minimizing
crosstalk is done by adding the RC network shown in the
block diagram (Figure 6)
b
’’ (minus sign) in front of the amplifier designation The
CC
b
A1 goes to the contrast and drive attenuator
The input video signal is buffered by
F capacitor to the input pin 6 There is no
being the most common impedance used
TL H 11831– 9
resistor at
b
A1 In