el2260c ETC-unknow, el2260c Datasheet - Page 12

• Manufacturer Part Number: el2260c
• Description: Dual/quad Current Feedback Amplifiers
• Manufacturer: ETC-unknow

Applications Information
Product Description
The EL2260C EL2460C are dual and quad cur-
rent mode feedback amplifiers that offer wide
bandwidths and good video specifications at
moderately low supply currents They are built
using Elantec’s proprietary complimentary bipo-
lar process and are offered in industry standard
pin-outs Due to the current feedback architec-
ture the EL2260C EL2460C closed-loop 3 dB
bandwidth is dependent on the value of the feed-
back resistor First the desired bandwidth is se-
lected by choosing the feedback resistor R
then the gain is set by picking the gain resistor
R
Performance Curves section show the effect of
varying both R
somewhat dependent on the power supply volt-
age As the supply voltage is decreased internal
junction capacitances increase causing a reduc-
tion 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 high-
ly recommended Lead lengths should be as short
as possible below
must be well bypassed to reduce the risk of oscil-
lation A 1 0
with a 0 01 F 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 in-
ductance Similarly capacitors should be low in-
ductance for best performance Use of sockets
particularly for the SO packages should be
avoided Sockets add parasitic inductance and ca-
pacitance which will result in peaking and over-
shoot
EL2260C EL2460C
Dual Quad 130 MHz Current Feedback Amplifiers
G
The curves at the beginning of the Typical
F
F tantalum capacitor in parallel
and R
G
The power supply pins
The 3 dB bandwidth is
F
and
12
Capacitance at the Inverting Input
Due to the topology of the current feedback am-
plifier stray capacitance at the inverting input
will affect the AC and transient performance of
the EL2260C EL2460C when operating in the
non-inverting configuration The characteristic
curve of gain vs frequency with variations of
C
trates how the bandwidth can be extended to be-
yond 200 MHz with some additional peaking
with an additional 2 pF of capacitance at the
V
ues of capacitance will be required to obtain simi-
lar 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 EL2260C and EL2460C have been designed
and specified with R
This value of feedback resistor yields extremely
flat frequency response with little to no peaking
out to 130 MHz As is the case with all current
feedback amplifiers wider bandwidth at the ex-
pense of slight peaking can be obtained by re-
ducing the value of the feedback resistor Inverse-
ly larger values of feedback resistor will cause
rolloff to occur at a lower frequency By reducing
R
170 MHz with under 1 dB of peaking Further
reduction of R
to 195 MHz with about 2 5 dB of peaking See
the curves in the Typical Performance Curves
section which show 3 dB bandwidth and peaking
vs frequency for various feedback resistors and
various supply voltages
Bandwidth vs Temperature
Whereas many amplifier’s supply current and
consequently 3 dB bandwidth drop off at high
temperature the EL2260C EL2460C were de-
signed to have little supply current variations
with temperature An immediate benefit from
this is that the 3 dB bandwidth does not drop off
drastically with temperature With V
and A
150 MHz to 110 MHz over the entire die junction
temperature range of 0 C
IN
IN
F
b
b
to 430
V
pin for the case of A
emphasizes this effect The curve illus-
e a
2 the bandwidth only varies from
F
bandwidth can be extended to
to 360
F
e
increases the bandwidth
k
560
V
T
e a
k
for A
150 C
2 Higher val-
S
V
e
e a
g
15V
2