LM1205N National Semiconductor, LM1205N Datasheet - Page 9

• 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 7 shows the timing of the clamp pulse relative to the
Functional Description
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 gives an attenuation
range from 0 dB to
for the drive attenuator is desirable and intentionally de-
signed because the drive is used only to balance the overall
gain of each color channel giving the correct color tempera-
ture on the CRT
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 LM1205 is
compared to the desired black level which is set at pin 19
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
sections have been designed to be identical except
has more current drive capability The output transistor
shown is part of
the user knows the configuration of the output stage
does not go to the outside world it is used for feeding back
the video signal for DC restoration Its output goes directly
b
A4 but has been shown separately so
b
6 dB A small gain adjustment range
(Continued)
b
A3 and
b
A4 Both
b
b
A4
A3
9
to the inverting input of the clamp comparator via the volt-
age divider formed by the 500
be close to the same output as
track due to the similar design of the two output stages
However the current at the output of
the current at the output of
load resistance of 390
the green video output pin to ground Another input to
is the blank pulse When a negative going blank pulse is
applied to pin 13 the output of the LM1205 is driven to less
than 0 1V above ground Using the timing shown in Figure 7
for the blank pulse the output of the LM1205 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 function of the LM1205
no grid blanking is necessary Note that the DC restoration
is done by feeding back the video signal from
blanking is done at
blanking can be done at the CRT cathodes and at the same
time activate the DC restoration loop
Note that V
pins are all internally connected For proper operation of the
LM1205 it is necessary to connect all the V
input power to the PCB and bypass each pin with a 0 1 F
capacitor V
output stages This is a separate power input from V
there are no internal connections between the two different
power inputs In some layouts pin 23 may need to be isolat-
ed by a 10
PCB Pin 23 must be bypassed by a parallel connection of a
10 F and 0 1 F capacitors The ground connection for the
LM1205 is 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 LM1205
CC1
CC2
resistor between it and the input power to the
goes to pins 3 11 22 and 25 These four
is the input power at pin 23 for the three
b
A4 By using the two output stages
needs to be connected from pin 20
b
A3 To balance both outputs a
and 4k resistors
b
A3 and will temperature
b
A4 will be ten times
CC1
pins to the
b
b
A3 but
A4 will
b
CC1
A4