EL2074C
400MHz GBWP Gain-of-2 Stable Operational Amplifier
The EL2074C has been designed to be among the best
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.
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
150W, 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.
Printed-Circuit Layout
The excellent output drive capability of the EL2074C
allows it to drive up to 4 back-terminated loads with
excellent video performance. With 4 150W 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 150W Loads.
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 1000W to 2000W
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.
Output Drive Capability
The EL2074C has been optimized to drive 50W and 75W
loads. It can easily drive 6VPP into a 50W load. This high
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 50W, capacitive loads will
decrease the amplifier's phase margin which may result
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