
8
EL1504C, EL1505C
Differential Line Driver
EL1504C,
E
L
1505C
Applications Information
The EL1504/5C consists of two power line drivers that
can be connected for full duplex differential line trans-
mission. The amplifiers are designed to be used with
signals up to 4 MHz and produce low distortion levels.
Here is a typical interface circuit:
The amplifiers are wired one in positive gain and the
other in negative gain configuration to generate a differ-
ential output for a single-ended input. The drivers will
exhibit very similar frequency responses for gains of
three or greater and thus generate very small common-
mode outputs over frequency, but for low gains the two
drivers RF’s need to be adjusted to give similar fre-
quency responses. The positive-gain driver will
generally exhibit more bandwidth and peaking than the
negative-gain driver. The Typical Performance Curves
section of this data sheet has a plot of driver responses
matched at gains of +1 and -1 using feedback resistors of
910
 and 750, respectively.
If a differential signal is available to the drive amplifiers,
they may be wired so:
Each amplifier has identical positive gain connections,
and optimum common-mode rejection occurs. Further,
DC input errors are duplicated and create common-
mode rather than differential line errors.
Input Connections
The drivers are somewhat sensitive to source imped-
ance. In particular, they do not like being driven by
inductive sources. More than 100 nH of source imped-
ance can cause ringing or even oscillations. This
inductance is equivalent to about 4” of unshielded wir-
ing, or 6” of unterminated transmission line. Normal
high-frequency construction obviates any such problem.
Resistive sources greater than 2 k
 will cause the driver
to exhibit increased harmonic distortion. Most amplifier
output stages are much lower in impedance and give no
problem.
Power Supplies & Dissipation
The EL1504/5C works well over the ±5V to ±15V sup-
ply range. Frequency response varies only slightly, and
output drive capability is constant. The major supply
voltage issue is power dissipation. The internal dissipa-
tion PD for an EL1504/5C running on supply voltages of
±VS and delivering a DC output voltage VO into a load
of RL is:
-
+
Driver Input
-
+
ZLINE
ROUT
RF
RG
ROUT
RF
RG
RIN
Figure 1. Typical Line Interface Connection
Figure 2. Drivers Wired for Differential Input
-
+
-
+
ROUT
RF
2RG
ROUT
RF
RG
ZLINE
Differential Input
P
D
2V
S
I
S
×
2V
S
V
O
–
()
×
+
×
V
O RL
×
=