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EL2075C

2GHz GBWP Gain-of-10 Stable Operational Amplifier

Applications Information

Product Description

The EL2075C is a wideband monolithic operational

amplifier built on a high-speed complementary bipolar

process. The EL2075C uses a classical voltage-feedback

topology which allows it to be used in a variety of appli-

cations requiring a noise gain

≥10 where current-

feedback amplifiers are not appropriate because of

restrictions placed upon the feedback element used with

the amplifier. The conventional topology of the

EL2075C allows, for example, a capacitor to be placed

in the feedback path, making it an excellent choice for

applications such as active filters, sample-and-holds, or

integrators. Similarly, because of the ability to use

diodes in the feedback network, the EL2075C is an

excellent choice for applications such as log amplifiers.

The EL2075C also has excellent DC specifications:

These specifications allow the EL2075C to be used in

DC-sensitive applications such as difference amplifiers.

Furthermore, the current noise of the EL2075C is only

3.2 pA/

√Hz, making it an excellent choice for high-sen-

sitivity transimpedance amplifier configurations.

Gain-Bandwidth Product

The EL2075C has a gain-bandwidth product of 2GHz.

For gains greater than 40, its closed-loop -3dB bandwidth

is approximately equal to the gain-bandwidth product

divided by the noise gain of the circuit. For gains less

than 40, higher-order poles in the amplifier's transfer

function contribute to even higher closed loop band-

widths. For example, the EL2075C has a -3dB bandwidth

of 400MHz at a gain of +10, dropping to 200MHz at a

gain of +20. It is important to note that the EL2075C has

been designed so that this “extra” bandwidth in low-gain

applications does not come at the expense of stability. As

seen in the typical performance curves, the EL2075C in a

gain of +10 only exhibits 1.5dB of peaking with a 100

Ω

load.

Output Drive Capability

The EL2075C has been optimized to drive 50

Ω and 75Ω

output drive capability makes the EL2075C an ideal

choice for RF and IF applications. Furthermore, the cur-

rent drive of the EL2075C remains a minimum of 50mA

at low temperatures. The EL2075C is current-limited at

the output, allowing it to withstand momentary shorts to

ground. However, power dissipation with the output

shorted can be in excess of the power-dissipation capa-

bilities of the package.

Capacitive Loads

Although the EL2075C has been optimized to drive

resistive loads as low as 50

Ω, capacitive loads will

decrease the amplifier's phase margin which may result

in peaking, overshoot, and possible oscillation. For opti-

mum AC performance, capacitive loads should be

reduced as much as possible or isolated via a series out-

put resistor. Coax lines can be driven, as long as they are

terminated with their characteristic impedance. When

properly terminated, the capacitance of coaxial cable

will not add to the capacitive load seen by the amplifier.

Capacitive loads greater than 10pF should be buffered

with a series resistor (Rs) to isolate the load capacitance

from the amplifier output. A curve of recommended Rs

vs Cload has been included for reference. Values of Rs

were chosen to maximize resulting bandwidth without

additional peaking.

Printed-Circuit Layout

As with any high-frequency device, good PCB layout is

necessary for optimum performance. Ground-plane con-

struction is highly recommended, as is good power

supply bypassing. A 1µF–10µF tantalum capacitor is

recommended in parallel with a 0.01µF ceramic capaci-

tor. All lead lengths should be as short as possible, and

all bypass capacitors should be as close to the device

pins as possible. Parasitic capacitances should be kept to

an absolute minimum at both inputs and at the output.

Resistor values should be kept under 1000

Ω to 2000Ω

because of the RC time constants associated with the

parasitic capacitance. Metal-film and carbon resistors

are both acceptable, use of wire-wound resistors is not

recommended because of parasitic inductance. Simi-

larly, capacitors should be low-inductance for best

performance. If possible, solder the EL2075C directly to

the PC board without a socket. Even high quality sockets