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EL2260CN

Dual/Quad 130 MHz Current Feedback Amplifiers

Elantec -> Intersil 

EL2260C EL2460C

Dual Quad 130 MHz Current Feedback Amplifiers

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 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 3 dB bandwidth is

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

The power supply pins

must be well bypassed to reduce the risk of oscil-

lation A 1 0 mF tantalum capacitor in parallel

with a 0 01 mF 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

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

CINb emphasizes this effect The curve illus-

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

VINb pin for the case of AV e a2 Higher val-

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 RF e 560X for AV e a2

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

RF to 430X bandwidth can be extended to

170 MHz with under 1 dB of peaking Further

reduction of RF to 360X increases the bandwidth

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 VS e g15V

and AV e a2 the bandwidth only varies from

150 MHz to 110 MHz over the entire die junction

temperature range of 0 C k T k 150 C

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