11

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

of the Typical Performance Curves section show the effect of

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

bandwidth can be extended to beyond 200MHz with some

additional peaking with an additional 2pF of capacitance at

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

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

to 360

Ω 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

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

±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)

EL2260, EL2460