9
input voltage range is within 100mV of ground (R
L
= 500Ω),
and the lower output voltage range is within 300mV of
ground. Upper input voltage range reaches 4.2V, and output
voltage range reaches 3.8V with a 5V supply and R
L
= 500Ω.
This results in a 3.5V output swing on a single 5V supply.
This wide output voltage range also allows single-supply
operation with a supply voltage as high as 36V or as low as
2.5V. On a single 2.5V supply, the EL2244 and EL2444 still
have 1V of output swing.
Gain-Bandwidth Product and the -3dB Bandwidth
The EL2244 and EL2444 have a gain-bandwidth product of
120MHz while using only 5.2mA of supply current per
amplifier. For gains greater than 4, their closed-loop -3dB
bandwidth is approximately equal to the gain-bandwidth
product divided by the noise gain of the circuit. For gains
less than 4, higher-order poles in the amplifiers' transfer
function contribute to even higher closed loop bandwidths.
For example, the EL2244 and EL2444 have a -3dB
bandwidth of 120MHz at a gain of +1, dropping to 60MHz at
a gain of +2. It is important to note that the EL2244 and
EL2444 have been 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
EL2244 and EL2444 in a gain of +1 only exhibit 1.0dB of
peaking with a 1kΩ load.
Video Performance
An industry-standard method of measuring the video
distortion of components such as the EL2244 and EL2444 is
to measure the amount of differential gain (dG) and
differential phase (dP) that they introduce. 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 (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 EL2244 and EL2444 have been designed as an
economical solution for applications requiring low video
distortion. They have 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 150Ω, with standard video test levels at the
input, the EL2244 and EL2444 exhibit dG and dP of only
0.04% and 0.15° at NTSC and PAL. Because dG and dP
can vary with different DC offsets, the video performance of
the EL2244 and EL2444 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.
Output Drive Capability
The EL2244 and EL2444 have been designed to drive low
impedance loads. They can easily drive 6V
PP
into a 150Ω
load. This high output drive capability makes the EL2244
and EL2444 an ideal choice for RF, IF and video
applications. Furthermore, the current drive of the EL2244
and EL2444 remains a minimum of 35mA at low
temperatures.
Printed-Circuit Layout
The EL2244 and EL2444 are 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. Lead 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 5kΩ 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 EL2244 and EL2444 Macromodel
This macromodel has been developed to assist the user in
simulating the EL2244 and EL2444 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
EL2244, EL2444
