EL2160CM-T13 데이터 시트보기 (PDF) - Elantec -> Intersil
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EL2160CM-T13 Datasheet PDF : 18 Pages
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EL2160C
180MHz Current Feedback Amplifier
Applications Information
Product Description
The EL2160C is a current mode feedback amplifier that
offers wide bandwidth and good video specifications at a
moderately low supply current. It is built using Elantec's
proprietary complimentary bipolar process and is
offered in industry standard pin-outs. Due to the current
feedback architecture, the EL2160C 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 ¼.
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 par-
asitic inductance. Similarly, capacitors should be low
inductance for best performance. Use of sockets, partic-
ularly for the SO package, 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 EL2160C when
operating in the non-inverting configuration. The char-
acteristic 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 vir-
tual ground and stray capacitance is therefore not “seen”
by the amplifier.
Feedback Resistor Values
The EL2160C has 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 feed-
back 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. Fur-
ther 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 conse-
quently 3dB bandwidth drop off at high temperature, the
EL2160C was designed to have little supply current
variations with temperature. An immediate benefit from
this is that the 3dB bandwidth does not drop off drasti-
cally with temperature. With VS = ±15V and AV = +2,
the bandwidth only varies from 150MHz to 110MHz
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