el2073 Intersil Corporation, el2073 Datasheet - Page 9

• Manufacturer Part Number: el2073
• Description: 200mhz Unity-gain Stable Operational Amplifier
• Manufacturer: Intersil Corporation

Video Performance
An industry-standard method of measuring the video
distortion of a component such as the EL2073 is to measure
the amount of differential gain (dG) and differential phase
(dP) that it introduces. To make these measurements, a
0.286V
offset (0 IRE) at either 3.58MHz for NTSC, 4.43MHz for PAL,
or 30MHz for HDTV. A second measurement is then made at
0.714V DC offset (100 IRE). Differential gain is a measure of
the change in amplitude of the sine wave, and is measured
in percent. Differential phase is a measure of the change in
phase, and is measured in degrees.
For signal transmission and distribution, a back-terminated
cable (75Ω in series at the drive end, and 75Ω to ground at
the receiving end) is preferred since the impedance match at
both ends will absorb any reflections. However, when double
termination is used, the received signal is halved; therefore a
gain of 2 configuration is typically used to compensate for
the attenuation.
The EL2073 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 150Ω, with
standard video test levels at the input, the EL2073 exhibits
dG and dP of only 0.01% and 0.015° at NTSC and PAL.
Because dG and dP vary with different DC offsets, the
superior video performance of the EL2073 has been
characterized over the entire DC offset 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 EL2073 allows it
to drive up to 4 back-terminated loads with excellent video
performance. With 4 150Ω loads, dG and dP are only 0.15%
and 0.08° at NTSC and PAL. For more information, refer to
the curves for Video Performance vs Number of 150Ω
Loads.
Output Drive Capability
The EL2073 has been optimized to drive 50Ω and 75Ω
loads. It can easily drive 6V
output drive capability makes the EL2073 an ideal choice for
RF, IF and video applications. Furthermore, the current drive
of the EL2073 remains a minimum of 50mA at low
temperatures. The EL2073 is current-limited at the output,
allowing it to withstand momentary shorts to ground.
However, power dissipation with the output shorted can be in
excess of the power-dissipation capabilities of the package.
Capacitive Loads
Although the EL2073 has been optimized to drive resistive
loads as low as 50Ω, capacitive loads will decrease the
amplifier's phase margin which may result in peaking,
overshoot, and possible oscillation. For optimum AC
PP
(40 IRE) signal is applied to the device with 0V DC
PP
9
into a 50Ω load. This high
EL2073
performance, capacitive loads should be reduced as much
as possible or isolated via a series output 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
construction is highly recommended, as is good power
supply bypassing. A 1µF–10µF tantalum capacitor is
recommended in parallel with a 0.01µF ceramic capacitor.
All pin 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 1000Ω 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. Similarly, capacitors should be low-
inductance for best performance. If possible, solder the
EL2073 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
degradation of AC performance due to parasitics, the use of
surface-mount components (resistors, capacitors, etc.) is
also recommended.