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EL2074C

400MHz GBWP Gain-of-2 Stable Operational Amplifier

The EL2074C has been designed to be among the best

video amplifiers in the marketplace today. It has been

thoroughly characterized for video performance in the

topology described above, and the results have been

included as minimum dG and dP specifications and as

typical performance curves. In a gain of +2, driving

150

Ω, with standard video test levels at the input, the

EL2074C exhibits dG and dP of only 0.01% and 0.015°

at NTSC and PAL. Because dG and dP vary with differ-

ent DC offsets, the superior video performance of the

EL2074C has been characterized over the entire DC off-

set range from -0.714V to +0.714V. For more

information, refer to the curves of dG and dP vs DC

Input Offset.

The excellent output drive capability of the EL2074C

allows it to drive up to 4 back-terminated loads with

excellent video performance. With 4 150

Ω loads, dG

and dP are only 0.15% and 0.08° at NTSC and PAL. For

more information, refer to the curves for Video Perfor-

mance vs Number of 150

Ω Loads.

Output Drive Capability

The EL2074C has been optimized to drive 50

Ω and 75Ω

output drive capability makes the EL2074C an ideal

choice for RF, IF and video applications. Furthermore,

the current drive of the EL2074C remains a minimum of

50mA at low temperatures. The EL2074C is current-

limited at the output, allowing it to withstand momen-

tary shorts to ground. However, power dissipation with

the output shorted can be in excess of the power-dissipa-

tion capabilities of the package.

Capacitive Loads

Although the EL2074C has been optimized to drive

resistive loads as low as 50

Ω, capacitive loads will

decrease the amplifier's phase margin which may result

in peaking, overshoot, and possible oscillation. For opti-

mum AC performance, capacitive loads should be

reduced as much as possible or isolated via a series out-

put resistor. Coax lines can be driven, as long as they are

terminated with their characteristic impedance. When

properly terminated, the capacitance of coaxial cable

will not add to the capacitive load seen by the amplifier.

Capacitive loads greater than 10pF should be buffered

with a series resistor (Rs) to isolate the load capacitance

from the amplifier output. A curve of recommended Rs

vs Cload has been included for reference. Values of Rs

were chosen to maximize resulting bandwidth without

peaking.

Printed-Circuit Layout

As with any high-frequency device, good PCB layout is

necessary for optimum performance. Ground-plane con-

struction is highly recommended, as is good power

supply bypassing. A 1 µF–10 µF tantalum capacitor is

recommended in parallel with a 0.01 µF ceramic capaci-

tor. All lead lengths should be as short as possible, and

all bypass capacitors should be as close to the device

pins as possible. Parasitic capacitances should be kept to

an absolute minimum at both inputs and at the output.

Resistor values should be kept under 1000

Ω to 2000Ω

because of the RC time constants associated with the

parasitic capacitance. Metal-film and carbon resistors

are both acceptable, use of wire-wound resistors is not

recommended because of parasitic inductance. Simi-

larly, capacitors should be low-inductance for best

performance. If possible, solder the EL2074C directly to

the PC board without a socket. Even high quality sockets

add parasitic capacitance and inductance which can

potentially degrade performance. Because of the degra-

dation of AC performance due to parasitics, the use of

surface-mount components (resistors, capacitors, etc.) is

also recommended.