Datasheet LM1203N Datasheet (NSC)

LM1203 RGB Video Amplifier System

LM1203 RGB Video Amplifier System

January 1996

General Description

The LM1203 is a wideband video amplifier system intended
for high resolution RGB color monitor applications. In addi­tion to three matched video amplifiers, the LM1203 contains
three gated differential input black level clamp comparators
for brightness control and three matched attenuator circuits
for contrast control. Each video amplifier contains a gain set
or ‘‘Drive’’ node for setting maximum system gain (Av

e

to 10) as well as providing trim capability. The LM1203 also
contains a voltage reference for the video inputs. For high
resolution monochrome monitor applications see the
LM1201 Video Amplifier System datasheet.

Block and Connection Diagram

Features

Y

Three wideband video amplifiers (70 MHz

Y

Inherently matched (g0.1 dB or 1.2%) attenuators for
contrast control

Y

Three externally gated comparators for brightness con­trol

Y

Provisions for independent gain control (Drive) of each

4

video amplifier

Y

Video input voltage reference

Y

Low impedance output driver

@

b

3dB)

FIGURE 1

Order Number LM1203N

See NS Package Number NA28F

C

1996 National Semiconductor Corporation RRD-B30M56/Printed in U. S. A.

TL/H/9178

TL/H/9178– 1

Absolute Maximum Ratings

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.

Supply Voltage, V

(Note 1) 13.5V

Voltage at Any Input Pin, V

Video Output Current, I16, 20 or 25 28 mA

Power Dissipation, P

(Above 25
Thermal Resistance, i
Junction Temperature, T

Pins 1, 13, 23, 28

CC

IN

D

C) Derate Based on iJAand T

§

JA

J

t

V

CC

t

V

GND

IN

2.5W

J

50§C/W

150§C

Storage Temperature Range, T

STG

b

65§Ctoa150§C

Lead Temperature, (Soldering, 10 sec.) 265§C

ESD susceptibility 1 kV

Human body model: 100 pF discharged through a 1.5 kX

resistor

Operating Ratings (Note 9)

Temperature Range 0

Supply Voltage (VCC) 10.8VsV

Cto70§C

§

s

CC

13.2V

Electrical Characteristics See Test Circuit

DC Static Tests S17, 21, 26 Open; V12

e

6V; V14e0V; V15e2.0V unless otherwise stated

(Figure 2)

,T

A

e

25§C; V

Label Parameter Conditions Typ

e

e

V

CC2

12V

CC1

Tested Design Units

Limit (Note 2) Limit (Note 3) (Limits)

Is Supply Current VCC1 only 73 90.0 mA(max)

V11 Video Input Reference Voltage

2.4

2.2 V(min)

2.6 V(max)

lb Video Input Bias Current Any One Amplifier 5.0 20 mA(max)

V14 l Clamp Gate Low Input Voltage Clamp Comparators On 1.2 0.8 V(max)

V14 h Clamp Gate High Input Voltage Clamp Comparators Off 1.6 2.0 V(min)

I14 l Clamp Gate Low Input Current V14e0V

b

0.5

b

5.0 mA(max)

I14 h Clamp Gate High Input Current V14e12V 0.005 1 mA(max)

lclampaClamp Cap Charge Current V5, 8 or 10e0V 850 500 mA(min)

lclampbClamp Cap Discharge Current V5, 8 or 10e5V

b

850

b

500 mA(min)

Vol Video Output Low Voltage V5, 8 or 10e0V 0.9 1.25 V(max)

Voh Video Output High Voltage V5, 8 or 10e5V 8.9 8.2 V(min)

DVo(2V) Video Output Offset Voltage Between Any Two Amplifiers

e

2V

V15

DVo(4V) Video Output Offset Voltage Between Any Two Amplifiers

V15e4V

AC Dynamic Tests S17, 21, 26 Closed; V14

e

0V; V15e4V; unless otherwise stated

Symbol Parameter Conditions Typ

Av max Video Amplifier Gain V12e12V, V

e

560 mVp-p 6.0 4.5 V/V(min)

IN

DAv 5V Attenuation@5V Ref: Av max, V12e5V

DAv 2V Attenuation@2V Ref: Av max, V12e2V

Av match Absolute gain match@Av max V12e12V (Note 5)

DAv track1 Gain change between amplifiers V12e5V (Notes 5, 8)

DAv track2 Gain change between amplifiers V12e2V (Notes 5, 8)

THD Video Amplifier Distortion V12e3V, V

e

1 Vp-p 0.5 %

O

f(b3 dB) Video Amplifier Bandwidth V12e12V,

e

(Notes 4, 6) V

t

r

t

f

Output Rise Time (Note 4) V

Output Fall Time (Note 4) V

100 mV

O

e

O

e

O

rms

4 Vp-p 5 ns

4 Vp-p 7 ns

g

0.5

g

0.5

g

50 mV(max)

g

50 mV(max)

Tested Design Units

Limit (Note 2) Limit (Note 3) (Limits)

b

10 dB

b

40 dB

g

0.5 dB

g

0.1

g

0.3

g

0.5 dB(max)

g

0.7 dB(max)

70 MHz

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AC Dynamic Tests S17, 21, 26 Closed; V14

Symbol Parameter Conditions Typ

Vsep Video Amplifier 10 kHz Isolation V12e12V (Note 7)
10 kHz

Vsep Video Amplifier 10 MHz Isolation V12e12V (Notes 4, 7)
10 MHz

Note 1: VCCsupply pins 1, 13, 23, 28 must be externally wired together to prevent internal damage during VCCpower on/off cycles.

Note 2: These parameters are guaranteed and 100% production tested.

Note 3: Design limits are guaranteed (but not 100% production tested). These limits are not used to calculate outgoing quality levels.

Note 4: When measuring video amplifier bandwidth or pulse rise and fall times, a double sided full ground plane printed circuit board without socket is recommend-

ed. Video Amplifier 10 MHz isolation test also requires this printed circuit board.

Note 5: Measure gain difference between any two amplifiers. V

Note 6: Adjust input frequency from 10 kHz (Av

Note 7: Measure output levels of the other two undriven amplifiers relative to driven amplifier to determine channel separation. Terminate the undriven amplifier

inputs to simulate generator loading. Repeat test at f

Note 8: DAv track is a measure of the ability of any two amplifiers to track each other and quantifies the matching of the three attenuators. It is the difference in
gain change between any two amplifiers with the Contrast Voltage V12 at either 5V or 2V measured relative to an Av max condition V12
Av max the three amplifiers gains might be 17.4 dB, 16.9 dB, and 16.4 dB and change to 7.3 dB, 6.9 dB, and 6.5 dB respectively for V12
measured typical

Note 9: Operating Ratings indicate conditions for which the device is functional. See Electrical Specifications for guaranteed performance limits.

g

0.1 dB channel tracking.

ref level) to theb3 dB corner frequency (fb3 dB).

max

e

10 MHz for Vsepe10 MHz.

IN

e

0V; V15e4V; unless otherwise stated (Continued)

Tested Design

Limit (Note 2) Limit (Note 3)

b

65 dB

b

46 dB

e

1 Vp-p.

IN

e

12V. For example, at

e

5V. This yields the

Units

*Peaking capacitors. See Frequency Response
using various peaking cups graph on next page.

FIGURE 2. LM1203 Test Circuit

TL/H/9178– 2

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Typical Performance Characteristics

Contrast vs Frequency

Frequency Response Using
Various Peaking Caps

TL/H/9178– 11

TL/H/9178– 13

Crosstalk vs Frequency

TL/H/9178– 12

Attenuation vs Contrast Voltage

TL/H/9178– 14

Pulse Response

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Rise & Fall Times

e

Vert.

e

Horiz.

– – GND

TL/H/9178– 15

1V/Div.

10 ns/Div.

FIGURE 3. LM1203 Typical Application

TL/H/9178– 3

* 30X resistors are added to the input pins for protection against current surges coming through the 10 mF input capacitors. By increasing these resistors to well
over 100X the rise and fall times of the LM1203 can be increased for EMI considerations.

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Applications Information

Figure 4

shows the block diagram of a typical analog RGB
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
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 in 75X at the monitor input and internally ac cou-

Figure 4

. Separate

pled to the video amplifiers. These input signals are approxi­mately 1 volt peak to peak in amplitude and at the input of
the high voltage video section, approximately 6V 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

Figure 4

GAIN AND DC CONTROL’’ describes the function of the
LM1203 which contains the three matched video amplifiers,
contrast control and brightness control.

block labeled ‘‘VIDEO AMPLIFICATION WITH

FIGURE 4. Typical RGB Color Monitor Block Diagram

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TL/H/9178– 4

Circuit Description

Figure 5

is a block diagram of one of the video amplifiers
along with the contrast and brightness controls. The con­trast control is a dc-operated attenuator which varies the ac
gain of all three amplifiers simultaneously while not introduc­ing any signal distortions or tracking errors. The brightness
control function requires a ‘‘sample and hold’’ circuit (black
level clamp) which holds the dc bias of the video amplifiers
and CRT cathodes constant during the black level reference
portion of the video waveform. The clamp comparator,
when gated on during this reference period, will charge or
discharge the clamp capacitor until the plus input of the
clamp comparator matches that of the minus input voltage
which was set by the brightness control.

Figure 6

is a simplified schematic of one of the three video
amplifiers along with the recommended external compo­nents. The IC pin numbers are circled with all external com­ponents shown outside of the dashed line. The video input
is applied to pin 6 via the 10 mF coupling capacitor. DC bias

to the video input is through the 10 kX resistor which is
connected to the 2.4V reference at pin 11. The low frequen­cy roll-off of the amplifier is set by these two components.
Transistor Q1 buffers the video signal to the base of Q2.
The Q2 collector current is then directed to the V
ply directly or through the 1k load resistor depending upon
the differential DC voltage at the bases of Q3 and Q4. The
Q3 and Q4 differential base voltage is determined by the
contrast control circuit which is described below. RF decou­pling capacitors are required at pins 2 and 3 to insure high
frequency isolation between the three video amplifiers
which share these common connections. The black level dc
voltage at the collector of Q4 is maintained by Q5 and Q6
which are part of the black level clamp circuit also described
below. The video signal appearing at the collector of Q4 is
then buffered by Q7 and level shifted down by Z1 and Q8 to
the base of Q9 which will then provide additional system
gain.

CC

1 sup-

FIGURE 5. Block Diagram of LM1203 Video Amplifier with Contrast and Black Level Control

TL/H/9178– 5

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Circuit Description (Continued)

TL/H/9178– 6

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FIGURE 6. Simplified LM1203 Video Amplifier Section with Recommended External Components

Circuit Description (Continued)

The ‘‘Drive’’ pin will allow the user to trim the Q9 gain of
each amplifier to correct for differences in the CRT and high
voltage cathode driver gain stages. A small capacitor
(33 pF) at this pin will extend the high frequency gain of the
video amplifier by compensating for some of the internal
high frequency roll off. To use this capacitor and still provide
variable gain adjustment, the 51X and series 100X pot
should be used with the red and green drive pins. The 91X
resistor used with the blue drive pin will set the system gain
to approximately 6.2 and allow adjustment of the red and
green gains to 6.2 plus or minus 25%. The video signal at
the collector of Q9 is buffered and level shifted down by
Q10 and Q11 to the base of the output emitter follower Q12.
Between the emitter of Q12 and the video output pin is a
40X resistor which was included to prevent spurious oscilla­tions when driving capacitive loads. An external emitter re­sistor must be added between the video output pin and
ground. The value of this resistor should not be less than
390X or package power limitations may be exceeded when
worst case (high supply, max supply current, max temp) cal­culations are made. If negative going pulse slewing is a
problem because of high capacitive loads (
efficient method of emitter pull down would be to connect a
suitable resistor to a negative supply voltage. This has the
effect of a current source pull down when the minus supply
voltage is

b

12V and the emitter current is approximately

l

10 pF), a more

10 mA. The system gain will also increase slightly because
less signal will be lost across the internal 40X resistor. Pre­cautions must be taken to prevent the video output pin from
going below ground because IC substrate currents may
cause erratic operation. The collector currents from the vid­eo output transistors are returned to the power supply at
V

2 pin 23. When making power dissipation calculations

CC

note that the data sheet specifies only the V
current at 12V. The IC power dissipation contribution of
V

2 is dependent upon the video output emitter pull down

CC

load.

CC

1 supply

In applications that require video amplifier shut down be­cause of fault conditions detected by monitor protection cir­cuits, pin 11 and the wiper arms of the contrast and bright­ness controls can be grounded without harming the IC. This
assumes some series resistance between the top of the
control pots and V

Figure 7

shows the internal construction of the pin 11 2.4V

CC

.

reference circuit which is used to provide temperature and
supply voltage tracking compensation for the video amplifier
inputs. The value of the external DC biasing resistors should
not be larger than 10 kX because minor differences in input
bias currents to the individual video amplifiers may cause
offsets in gain.

FIGURE 7. LM1203 Video Input Voltage Reference and Contrast Control Circuits

TL/H/9178– 7

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Circuit Description (Continued)

Figure 7

also shows how the contrast control circuit is con-

figured. Resistors R23, 24, diodes D3, 4 and transistor Q13
are used to establish a low impedance zero TC half supply
voltage reference at the base of Q14. The differential ampli­fier formed by Q15, 16 and feedback transistor Q17 along
with resistors R27, 28 establish a diferential base voltage
for Q3 and Q4 in
tracting current from the collector of Q16, a new differential
voltage is generated that reflects the change in the ratio of
currents in Q15 and Q16. To provide voltage control of the
Q16 current, resistor R29 is added between the Q16 collec­tor and pin 12. A capacitor should be added from pin 12 to
ground to prevent noise from the contrast control pot from
entering the IC.

Figure 8

clamp comparator sections of the LM1203. The clamp gate
circuit consists of a PNP input buffer transistor (Q18), a PNP
emitter coupled pair referenced on one side to 2.1V (Q19,

20) and an output switch (Q21). When the clamp gate input
at pin 14 is high (

Figure 6

. When externally adding or sub-

is a simplified schematic of the clamp gate and

l

1.5V) the Q21 switch is on and shunts

the I1 850 mA current to ground. When pin 14 is low (

k

1.3V)
the Q21 switch is off and the I1 850 mA current source is
mirrored or ‘‘turned around’’ by reference diode D5 and Q26
to provide a 850 mA current source for the clamp compara­tor(s). The inputs to the comparator are similar to the clamp
gate input except that an NPN emitter coupled pair is used
to control the current which will charge or discharge the
clamp capacitors at pins 5, 8, or 10. PNP transistors are
used at the inputs because they offer a number of advan­tages over NPNs. PNPs will operate with base voltages at or
near ground and will usually have a greater reverse emitter
base breakdown voltage (BVebo). Because the differential
input voltage to the clamp comparator during the video scan
period could be greater than the BVebo of NPN transistors a
resistor (R34) with a value one half that of R33 or R35 is
connected between the bases of Q23 and Q27. This resis­tor will limit the maximum differential input to Q24, 25 to
approximately 350 mV. The clamp comparator common
mode range is from ground to approximately 9V and the
maximum differential input voltage is V

and ground.

CC

FIGURE 8. Simplified Schematic of LM1203 Clamp Gate and Clamp Comparator Circuits

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TL/H/9178– 8

Additional Applications of the LM1203

Figure 9

shows how the LM1203 can be set up as a video
buffer which could be used in low cost video switcher appli­cations. Pin 14 is tied high to turn off the clamp compara­tors. The comparator input pins should be grounded as
shown. Sync tip (black level if sync is not included) clamping
is provided by diodes at the amplifier inputs. Note that the
clamp cap pins are tied to the Pin 11 2.4V reference. This
was done, along with the choice of 200X for the drive pin
resistor, to establish an optimum DC output voltage. The

contrast control (Pin 12) will provide the necessary gain or
attenuation required for channel balancing. Changing the
contrast control setting will cause minor DC shifts at the
amplifier output which will not be objectionable as the out­put is AC coupled to the load. The dual NPN/PNP emitter
follower will provide a low impedance output drive to the AC
coupled 75X output impedance setting resistor. The dual
500 mF capacitors will set the low frequency response to
approximately 4 Hz.

FIGURE 9. RGB Video Buffer with Diode Sync Tip Clamps and 75X Cable Driver

TL/H/9178– 9

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Additional Applications of the LM1203 (Continued)

When diode D4 at Pin 11 is switched to ground the input
video signals will be DC shifted down and clamped at a
voltage near ground (approximately 250 mV). This will dis­able the video amplifiers and force the output DC level low.
The DC outputs from other similarly configured LM1203s
could overide this lower DC level and provide the output
signals to the 75 X cable drivers. In this case any additional
LM1203s would share the same 390X output resistor. The
maximum DC plus peak white output voltage should not be
allowed to exceed 7V because the ‘‘off’’ amplifier output
stage could suffer internal zener damage. See
text for a description of the internal configuration of the vid­eo amplifier.

Figure 3

and

Figure 10

frequency amplifier with non gated DC feedback. Pin 14 is
tied low to turn on the clamp comparators (feedback amplifi­ers). The inverting inputs (Pins 17, 21, 26) are connected to
the amplifier outputs from a low pass filter. Additional low
frequency filtering is provided by the clamp caps. The drive
resistors can be made variable or fixed at values between 0
and 300X. Maximum output swings are achieved when the
DC output is set to approximately 4V. The high frequency
response will be dependent upon external peaking at the
drive pins.

shows the configuration for a three channel high

FIGURE 10. Three Channel High Frequency Amplifier with Non-gated DC Feedback (Non-video Applications)

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TL/H/9178– 10

FIGURE 11. LM1203/LM1881 Application Circuit for PC Board

TL/H/9178– 16

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TL/H/9178– 17

PC Board with Components

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Physical Dimensions inches (millimeters) unless otherwise noted Lit.

LM1203 RGB Video Amplifier System

28-Lead Molded Dual-In-Line Package (N)

Order Number LM1203N

NS Package Number NA28F

Ý

107315

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