EL2045C
Low-Power 100 MHz Gain-of-2 Stable Operational Amplifier
though stable with all capacitive loads, some
Applications Information Ð Contd.
peaking still occurs as load capacitance increases.
for video performance in the topology described
A series resistor at the output of the EL2045C
above, and the results have been included as typi-
can be used to reduce this peaking and further
cal dG and dP specifications and as typical per-
improve stability.
a
formance curves. In a gain of 2, driving 150X,
with standard video test levels at the input, the
EL2045C exhibits dG and dP of only 0.02% and
Printed-Circuit Layout
The EL2045C is well behaved, and easy to apply
in most applications. However, a few simple tech-
niques 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 recommend-
ed, as is good power supply bypassing. A 0.1 mF
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 per-
formance, parasitic capacitances should be kept
to a minimum at both inputs and at the output.
Resistor values should be kept under 5 kX be-
cause 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.
0.07 at NTSC and PAL. Because dG and dP can
vary with different DC offsets, the video per-
formance of the EL2045C has been characterized
§
b
over the entire DC offset range from 0.714V to
0.714V. For more information, refer to the
a
curves of dG and dP vs DC Input Offset.
The output drive capability of the EL2045C al-
lows it to drive up to 2 back-terminated loads
with good video performance. For more demand-
ing 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 EL2045C has been designed to drive low im-
pedance loads. It can easily drive 6 V
into a
PP
150X load. This high output drive capability
makes the EL2045C an ideal choice for RF, IF
and video applications. Furthermore, the current
drive of the EL2045C remains a minimum of
35 mA at low temperatures. The EL2045C is cur-
rent-limited at the output, allowing it to with-
stand shorts to ground. However, power dissipa-
tion with the output shorted can be in excess of
the power-dissipation capabilities of the package.
The EL2045C Macromodel
This macromodel has been developed to assist
the user in simulating the EL2045C with sur-
rounding 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.
Capacitive Loads
For ease of use, the EL2045C has been designed
to drive any capacitive load. However, the
EL2045C remains stable by automatically reduc-
ing its gain-bandwidth product as capacitive load
increases. Therefore, for maximum bandwidth,
capacitive loads should be reduced as much as
possible or isolated via a series output resistor
(Rs). Similarly, coax lines can be driven, but best
AC performance is obtained when they are termi-
nated with their characteristic impedance so that
the capacitance of the coaxial cable will not add
to the capacitive load seen by the amplifier. Al-
The model does not simulate these characteristics
accurately:
noise
non-linearities
temperature effects
manufacturing variations
settling-time
CMRR
PSRR
10
ELANTEC [ ELANTEC SEMICONDUCTOR ]
