EL1519
Capacitance at the Inverting Input
Due to the topology of the current feedback amplifier, stray
capacitance at the inverting input will affect the AC and
transient performance of the EL1519 when operating in the
non-inverting configuration.
In the inverting gain mode, added capacitance at the
inverting input has little effect since this point is at a virtual
ground and stray capacitance is therefore not “seen” by the
amplifier.
Supply Voltage Range
The EL1519 has been designed to operate with supply
voltages from ±2.5V to ±6V. Optimum bandwidth, slew rate,
and video characteristics are obtained at higher supply
voltages. However, at ±2.5V supplies, the 3dB bandwidth at
A
V
= +2 is a respectable 40MHz.
Single Supply Operation
If a single supply is desired, values from +5V to +12V can be
used as long as the input common mode range is not
exceeded. When using a single supply, be sure to either 1)
DC bias the inputs at an appropriate common mode voltage
and AC couple the signal, or 2) ensure the driving signal is
within the common mode range of the EL1519.
Feedback Resistor Values
The EL1519 has been designed and specified with
R
F
=750Ω for A
V
= +5. This value of feedback resistor yields
extremely flat frequency response with little to no peaking
out to 50MHz. As is the case with all current feedback
amplifiers, wider bandwidth, at the expense of slight
peaking, can be obtained by reducing the value of the
feedback resistor. Inversely, larger values of feedback
resistor will cause rolloff to occur at a lower frequency. See
the curves in the Typical Performance Curves section which
show 3dB bandwidth and peaking vs. frequency for various
feedback resistors and various supply voltages.
ADSL CPE Applications
The EL1519 is designed as a line driver for ADSL CPE
modems. It is capable of outputting 250mA of output current
with a typical supply voltage headroom of 1.3V. It can
achieve -85dBc of distortion at low 7.1mA of supply current
per amplifier.
The average line power requirement for the ADSL CPE
application is 13dBm (20mW) into a 100Ω line. The average
line voltage is 1.41V
RMS
. The ADSL DMT peak to average
ratio (crest factor) of 5.3 implies peak voltage of 7.5V into the
line. Using a differential drive configuration and transformer
coupling with standard back termination, a transformer ratio
of 1:2 is selected. The circuit configuration is as shown
below.
+
-
Bandwidth vs Temperature
Whereas many amplifier's supply current and consequently
3dB bandwidth drop off at high temperature, the EL1519 was
designed to have little supply current variations with
temperature. An immediate benefit from this is that the 3dB
bandwidth does not drop off drastically with temperature.
12.5
TX1
100
1K
AFE
338Ω
+
-
1:2
12.5
1K
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Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and
reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
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8
FN7017.2
April 10, 2007
INTERSIL [ INTERSIL CORPORATION ]
