EL2003C データシートの表示（PDF） - Elantec -> Intersil

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EL2003C

100MHz Video Line Driver

Elantec -> Intersil 

EL2003C, EL2033C

100MHz Video Line Driver

Driving Cables

There are at least three ways to use the EL2003C and

EL2033C to drive cables, as shown in the adjacent fig-

ure. The most obvious is to directly connect the cable to

the output of the buffer. This results in a gain determined

by the output resistance of the EL2003C or EL2033C

and the characteristic impedance of the cable, assuming

it is properly terminated. For RG-58 into 50Ω the gain is

about -1dB, exclusive of cable losses. For optimum

response and minimum reflections it is important for the

cable to be properly terminated.

Double termination of a cable is the cleanest way to

drive it since reflections are absorbed on both ends of the

cable. The cable source resistor is equal to the character-

istic impedance of the cable less the output resistance of

the EL2003C and EL2033C. The gain is -6dB exclusive

of the cable attenuation.

Back matching is the last and most interesting way to

drive a cable. The cable source resistor is again the char-

acteristic impedance less the output resistance of the

EL2003C and EL2033C; the termination resistance is

now much greater than the cable impedance. The gain is

0dB and DC levels waste no power.

An additional EL2003C or EL2033C make a good

receiver at the terminating end. Because an unterminated

cable looks like a resonant circuit, the receiving

EL2003C or EL2033C should have an isolating resistor

in series with its input to prevent oscillations when the

cable is not connected to the driver. Of course if the

cable is always connected to the back match, no resistor

is necessary.

WARNING: ONE END OF A CABLE MUST BE

PROPERLY TERMINATED. If neither end is termi-

nated in the cable characteristic impedance, the cable

will have standing waves that appear as resonances in

the frequency response. The resonant frequencies are a

function of the cable length and even relatively short

cables can cause problems at frequencies as low as

1MHz. Longer cables should be terminated on both

ends.

Direct Drive

Double Matched

Back Matched

Op Amp Booster

The EL2003C or EL2033C can boost the output drive of

almost any monolithic op amp. Because the phase shift

in the EL2003C and EL2033C is low at the op amp's

unity gain frequency, no additional compensation is

required. By following an op amp with an EL2003C or

EL2033C, the buffered op amp can drive cables and

other low impedance loads directly. Even decompen-

sated high speed op amps can take advantage of the

EL2003C’s or EL2033C’s 100mA drive.

Op Amp Booster

Driving capacitive loads with any closed loop amplifier

creates special problems. The open loop output imped-

ance works into the load capacitance to generate phase

lag which can make the loop unstable. The output

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