EL2460 データシートの表示（PDF） - Intersil
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EL2460 Datasheet PDF : 15 Pages
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EL2260, EL2460
Applications Information
Product Description
The EL2260/EL2460 are dual and quad current mode
feedback amplifiers that offer wide bandwidths and good
video specifications at moderately low supply currents. They
are built using Elantec’s proprietary complimentary bipolar
process and are offered in industry standard pinouts. Due to
the current feedback architecture, the EL2260/EL2460
closed-loop 3dB bandwidth is dependent on the value of the
feedback resistor. First the desired bandwidth is selected by
choosing the feedback resistor, RF, and then the gain is set
by picking the gain resistor, RG. The curves at the beginning
of the Typical Performance Curves section show the effect of
varying both RF and RG. The 3dB bandwidth is somewhat
dependent on the power supply voltage. As the supply
voltage is decreased, internal junction capacitances
increase, causing a reduction in closed loop bandwidth. To
compensate for this, smaller values of feedback resistor can
be used at lower supply voltages.
Power Supply Bypassing and Printed Circuit
Board Layout
As with any high frequency device, good printed circuit board
layout is necessary for optimum performance. Ground plane
construction is highly recommended. Lead lengths should be
as short as possible, below 1/4”. The power supply pins must
be well bypassed to reduce the risk of oscillation. A 1.0µF
tantalum capacitor in parallel with a 0.01µF ceramic
capacitor is adequate for each supply pin.
For good AC performance, parasitic capacitances should be
kept to a minimum, especially at the inverting input (see
Capacitance at the Inverting Input section). This implies
keeping the ground plane away from this pin. Carbon
resistors are acceptable, while use of wire-wound resistors
should not be used because of their parasitic inductance.
Similarly, capacitors should be low inductance for best
performance. Use of sockets, particularly for the SO
packages, should be avoided. Sockets add parasitic
inductance and capacitance which will result in peaking and
overshoot.
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 EL2260/EL2460 when
operating in the non-inverting configuration. The
characteristic curve of gain vs. frequency with variations of
CIN- emphasizes this effect. The curve illustrates how the
bandwidth can be extended to beyond 200MHz with some
additional peaking with an additional 2pF of capacitance at
the VIN- pin for the case of AV = +2. Higher values of
capacitance will be required to obtain similar effects at
higher gains.
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.
Feedback Resistor Values
The EL2260 and EL2460 have been designed and specified
with RF = 560Ω for AV = +2. This value of feedback resistor
yields extremely flat frequency response with little to no
peaking out to 130MHz. 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. By
reducing RF to 430Ω, bandwidth can be extended to
170MHz with under 1dB of peaking. Further reduction of RF
to 360Ω increases the bandwidth to 195MHz with about
2.5dB of peaking. 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.
Bandwidth vs Temperature
Whereas many amplifier’s supply current and consequently
3dB bandwidth drop off at high temperature, the
EL2260/EL2460 were 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. With VS = ±15V and AV = +2, the bandwidth
only varies from 150MHz to 110MHz over the entire die
junction temperature range of 0°C < T < 150°C.
Supply Voltage Range
The EL2260/EL2460 has been designed to operate with
supply voltages from ±2V to ±15V. Optimum bandwidth, slew
rate, and video characteristics are obtained at higher supply
voltages. However, at ±2V supplies, the 3dB bandwidth at
AV = +2 is a respectable 70MHz. The following figure is an
oscilloscope plot of the EL2260 at ±2V supplies, AV = +2,
RF = RG = 560Ω, driving a load of 150Ω, showing a clean
±600mV signal at the output.
If a single supply is desired, values from +4V to +30V can be
used as long as the input common mode range is not
exceeded. When using a single supply, be sure to either 1)
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