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EL2360CS

Triple 130 MHz Current Feedback Amplifier

Elantec -> Intersil 

EL2360C

Triple 130 MHz Current Feedback Amplifier

Applications Information

Product Description

The EL2360C is a triple current feedback ampli-

fier that offers wide bandwidth and good video

specifications at moderately low supply currents

It is built using Elantec’s proprietary compli-

mentary bipolar process and is offered in both a

16 pin PDIP and SOIC packages Due to the cur-

rent feedback architecture the EL2360C clo-

sedbloop b3 dB 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 a

gain resistor RG The curves at the beginning of

the Typical Performance Curves section show the

effect of varying both RF and RG The b3 dB

bandwidth is somewhat dependent on the power

supply voltage As the supply voltage is de-

creased internal junction capacitances increase

causing a reduction in the closed loop bandwidth

To compensate for this smaller values of feed-

back resistor can be used at lower supply volt-

ages

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 preferably below ’’ The power sup-

ply pins must be well bypassed to reduce the risk

of oscillation The combination of a 1 0 mF tanta-

lum capacitor in parallel with a 0 01 mF ceramic

capacitor has been shown to work well when

placed at each supply pin

For good AC performance parasitic capacitance

should be kept to a minimum especially at the

inverting input (see the Capacitance at the In-

verting Input section) This implies keeping the

ground plane away from this pin Carbon or Met-

al-Film resistors are acceptable with the Metal-

Film resistors giving slightly less peaking and

bandwidth because of their additional series in-

ductance Use of sockets particularly for the SO

package should be avoided if possible Sockets

add parasitic inductance and capacitance which

will result in some additional peaking and over-

shoot

Capacitance at the Inverting Input

Any manufacturer’s high-speed voltage- or cur-

rent-feedback amplifier can be affected by stray

capacitance at the inverting input The character-

istic curve of gain vs frequency with variations

in 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 2pF of capacitance at the

VINb pin For inverting gains this parasitic ca-

pacitance has little effect because the inverting

input is a virtual ground but for non-inverting

gains this capacitance (in conjunction with the

feedback and gain resistors) creates a pole in the

feedback path of the amplifier This pole if low

enough in frequency has the same destabilizing

effect as a zero in the forward open-loop re-

sponse The use of large value feedback and gain

resistors further exacerbates the problem by fur-

ther lowering the pole frequency

Feedback Resistor Values

The EL2360C has been designed and specified at

a gain of a2 with RF e 560X This value of

feedback resistor yields relatively flat frequency

response with little to no peaking out to 130

MHz Since the EL2360C is a current-feedback

amplifier it is also possible to change the value

of RF to get more bandwidth As seen in the

curve of Frequency Response For Various RF

and RG bandwidth and peaking can be easily

modified by varying the value of the feedback

resistor For example by reducing RF to 430X

bandwidth can be extended to 170 MHz with un-

der 1 dB of peaking Further reduction of RF to

360X increases the bandwidth to 195 MHz with

about 2 5 dB of peaking

Bandwidth vs Temperature

Whereas many amplifier’s supply current and

consequently b3 dB bandwidth drop off at high

temperature the EL2360C was designed to have

little supply current variation with temperature

An immediate benefit from this is that the b3

dB bandwidth does not drop off drastically with

temperature With VS e g15V and AV e a2

the bandwidth varies only from 150 MHz to 110

MHz over the entire die junction temperature

range of b50 C k T k 150 C

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