Application Information

GENERAL INFORMATION

The LM6310 is a high speed complementary bipolar amplifi-

er with good video performance The output of the LM6310

can be turned off with a logic level signal on the DISABLE

pin The output then goes to a high impedance state

(TRI-STATE) which makes it easy to multiplex signals with

the LM6310 The LM6310 responds very quickly to the DIS-

ABLE input (under 25 ns) making it useful for video effects

and adding or selecting data from video streams such as

TELTEXT

Note

The LM6310 will operate normally when there is no connection to the

DISABLE pin

The LM6310 has low power consumption for a high speed

typical current consumption drops below 10 mA This

makes the LM6310 ideal for portable video equipment

The LM6310 is available in two package types DIPs for

through hole designs and SO-8 surface mount packages

The LM6310 uses a current feedback design to achieve

good video performance at low current and low cost

Benefits of the LM6310

The LM6310 provides good video performance for consum-

er and portable applications at low current and low cost

The disable option can reduce power consumption in porta-

ble applications

The video multiplexing capability of the disable function can

also be used to improve the testability of systems by provid-

ing an easy means to open the analog signal path and insert

test or reference signals

Since the multiplexing configuration is a function of the out-

put and disable signal wiring using multiple LM6310’s has

some strong advantages over a one chip video multiplexer

First larger multiplexers are possiblewith careful layout

up to 8 video inputs can be multiplexed

Frequently in multiplexer designs one or more of the input

signals will need to be buffered with an amplifier and the

output may also need a buffer or driver amplifier Wiring up

LM6310s to do multiplexing lets the LM6310 act as both the

input buffer and the output driver This can reduce parts and

save money In addition to reducing cost the signals will go

through fewer amplifiers This can mean improved signal

quality in addition to lower cost

DESIGN ADAPTABILITY AND SYSTEM

DESIGN FLEXIBILITY

Using the LM6310 allows more adaptable cost effective de-

sign If you need a 3 input multiplexer you can make one

avoiding the extra cost of unused devices of quad multiplex-

er If you need a 5 input multiplexer you can design this with

5 LM6310s saving the space and cost of two video multi-

plexer chips

Using the LM6310 on a distributed multiplexer can improve

manufacturing flexibility You can design a low cost system

with the minimal number functions needed for the low end

of the market

Additional functions (close captioning

TELETEXT digital video information services etc) can be

designed on to add-in cards Since the LM6310 will operate

normally when the DISABLE input is floating (no con-

nection) the additional functions can be built on the add-in

cards By using LM6310s on both the basic board and the

add-in cards

video and other signals can be digitally

switched to implement the new add-in functions Using

LM6310s avoids adding the cost of a dedicated multiplexer

in the low cost system and increases design flexibility

EASY TO USE COST-EFFECTIVE CURRENT FEEDBACK

When used with good high speed layout in a circuit like

those shown in the section on typical performance curves

the LM6310 will provide wide bandwidth high slew and

good video performance Modern current feedback devices

can provide higher bandwidth at lower current and at lower

cost than conventional voltage feedback devices

Note on Performance Curves and

Datasheet Limits

Important

Performance curves represent an average of parts and are not

limits

COMMON MODE REJECTION RATIO

The CMRR of 50 dB is valid for inputs which are within 1V of

rails Moving the inputs away from the center of the supplies

will result in reduced performance and non-linearities

CURRENT vs TEMPERATURE

This curve is relatively flat over temperature (typically under

1 mA) that even an input source impedance of 2 kX will

result in only a millivolt shift on the input voltage

OUTPUT VOLTAGE SWING vs LOAD

This curve shows that almost all of the output swing is avail-

able for the 150X loads usually used in back-terminated

75X video systems

OUTPUT SIGNAL ISOLATION IN DISABLE MODE

The top graph shows the spectrum analyzer output of an

LM6310 in normal operaiton The 4 MHz peak has an ampli-

tude of 69 mV Note that the reference level is 100 millivolts

(100 mV) second and third harmonics are present and the

noise floor is towards the bottom of the graph

With the LM6310 disabled we need to greatly increase the

gain of the spectrum analyzer to see the feedthrough of the

4 MHz signal Note that the reference level is now 50 micro-

volts (50 mV) and the noise floor is towards the middle of

the graph The 4 MHz signal now has an amplitude of

289 mV less than one-thousandth the normal signal

Note that the LM6310 will function normally (output on) with

the DISABLE input (pin 8) left floating (not connected)

PULSE RESPONSE AND GAIN vs FREQUENCY

photo is 1 kX A value of 1 kX to2kX is recommended for

gain and phase plots

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