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FN7030.1
February 11, 2005
designed so that this “extra” bandwidth in low-gain
applications does not come at the expense of stability. As
seen in the typical performance curves, the EL2045 in a gain
of +2 only exhibits 1.0dB of peaking with a 1k load.
Video Performance
An industry-standard method of measuring the video
distortion of a component such as the EL2045 is to measure
the amount of differential gain (dG) and differential phase
(dP) that it introduces. To make these measurements, a
0.286V
PP
(40 IRE) signal is applied to the device with 0V DC
offset (0 IRE) at either 3.58MHz for NTSC or 4.43MHz for
PAL. 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 (75 in series at the drive end, and 75 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 EL2045 has been designed as an economical solution
for applications requiring low video distortion. It has been
thoroughly characterized for video performance in the
topology described above, and the results have been
included as typical dG and dP specifications and as typical
performance curves. In a gain of +2, driving 150, with
standard video test levels at the input, the EL2045 exhibits
dG and dP of only 0.02% and 0.07° at NTSC and PAL.
Because dG and dP can vary with different DC offsets, the
video performance of the EL2045 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 output drive capability of the EL2045 allows it to drive up
to 2 back-terminated loads with good video performance.
For more demanding applications such as greater output
drive or better video distortion, a number of alternatives such
as the EL2120, EL400, or EL2074 should be considered.
Output Drive Capability
The EL2045 has been designed to drive low impedance
loads. It can easily drive 6V
PP
into a 150 load. This high
output drive capability makes the EL2045 an ideal choice for
RF, IF and video applications. Furthermore, the current drive
of the EL2045 remains a minimum of 35mA at low
temperatures.
Printed-Circuit Layout
The EL2045 is well behaved, and easy to apply in most
applications. However, a few simple techniques will help
assure rapid, high quality results. 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 0.1µF
ceramic capacitor is recommended for bypassing both
supplies. Pin lengths should be as short as possible, and
bypass capacitors should be as close to the device pins as
possible. For good AC performance, parasitic capacitances
should be kept to a minimum at both inputs and at the
output. Resistor values should be kept under 5k 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 their parasitic inductance. Similarly, capacitors
should be low-inductance for best performance.
The EL2045 Macromodel
This macromodel has been developed to assist the user in
simulating the EL2045 with surrounding circuitry. It has been
developed for the PSPICE simulator (copywritten by the
Microsim Corporation), and may need to be rearranged for
other simulators. It approximates DC, AC, and transient
response for resistive loads, but does not accurately model
capacitive loading. This model is slightly more complicated
than the models used for low-frequency op-amps, but it is
much more accurate for AC analysis.
The model does not simulate these characteristics
accurately:
•Noise
•Settling time
• Non-linearities
• Temperature effects
• Manufacturing variations
•CMRR
• PSRR
EL2045
