EL2030C
120 MHz Current Feedback Amplifier
An industry standard way of measuring the dis-
Application Information
tortion of a video component (or system) is to
measure the amount of differential gain and
phase error it introduces. A 100 mV peak to peak
sine wave at 3.58 MHz for NTSC (4.3 MHz for
PAL), with 0V DC component serves as the refer-
ence. The reference signal is added to a DC offset,
shifting the sine wave from 0V to 0.7V which is
then applied to the device under test (DUT). The
output signal from the DUT is compared to the
reference signal. The Differential Gain is a mea-
sure of the change in amplitude of the sine wave
and is measured in percent. The Differential
Phase is a measure of the change in the phase of
the sine wave and is measured in degrees. Typi-
cally, the maximum positive and negative devia-
tions are summed to give peak differential gain
and differential phase errors. The test setup in
Figure 1 was used to characterize the EL2030.
For higher than NTSC and PAL frequencies, an
alternate Differential Gain and Phase measure-
ment can be made using an HP3577A Network
Analyser and the setup shown in Figure 2. The
frequency response is normalized to gain or phase
with 0V DC at the input. From the normalized
value a DC offset voltage is introduced and the
Differential Gain or Phase is the deviation from
the normalized value.
Product Description
The EL2030 is a current mode feedback amplifier
similar to the industry standard EL2020, but
with greatly improved AC characteristics. Most
significant among these are the extremely wide
bandwidth and very low differential gain and
phase. In addition, the EL2030 is fully character-
g
g
ized and tested at 5V and 15V supplies.
Power Supply Bypassing/Lead Dressing
It is important to bypass the power supplies of
the EL2030 with 0.1 mF ceramic disc capacitors.
Although the lead length is not critical, it should
not be more the (/2 inch from the IC pins. Failure
to do this will result in oscillation, and possible
destruction of the part. Another important detail
is the lead length of the inputs. The inputs
should be designed with minimum stray capaci-
tance and short lead lengths to avoid ringing and
distortion.
Latch Mode
The EL2030 can be damaged in certain circum-
stances resulting in catastrophic failure in which
destructive supply currents flow in the device.
g
Specifically, an input signal greater than
5
volts at currents greater than 5 mA is applied to
the device when the power supply voltages are
zero will result in failure of the device.
Video Applications
The video signals that must be transmitted for
modest distances are usually amplified by a de-
vice such as the EL2030 and carried via coax ca-
ble. There are at least two ways to drive cables,
single terminated and double terminated.
In addition, the EL2030 will be destroyed or
damaged in the same way for momentary power
supply voltage reversals. This could happen, for
example, during a power turn on transient, or if
the power supply voltages were oscillating and
the positive rail were instantaneously negative
with respect to the negative rail or vice versa.
When driving a cable, it is important to termi-
nate it properly to avoid unwanted signal reflec-
tions. Single termination (75X to ground at re-
ceive end) may be sufficient for less demanding
applications. In general, a double terminated ca-
ble (75X in series at drive end and 75X to ground
at receive end) is preferred since the impedance
match at both ends of the line will absorb signal
reflections. However, when double termination is
used (a total impedance of 150X), the received
signal is reduced by half; therefore, the amplifier
is usually set at a gain of 2 or higher to compen-
sate for attenuation.
Differential Gain and Differential Phase
Composite video signals contain intensity, color,
hue, timing and audio information in AM, FM,
and Phase Modulation. These video signals pass
through many stages during their production,
processing, archiving and transmission. It is im-
portant that each stage not corrupt these signals
to provide a ‘‘high fidelity’’ image to the end
viewer.
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ELANTEC [ ELANTEC SEMICONDUCTOR ]
