9

and the lower output voltage range is within 300mV of

ground. Upper input voltage range reaches 4.2V, and output

This results in a 3.5V output swing on a single 5V supply.

This wide output voltage range also allows single-supply

operation with a supply voltage as high as 36V or as low as

2.5V. On a single 2.5V supply, the EL2244 and EL2444 still

have 1V of output swing.

Gain-Bandwidth Product and the -3dB Bandwidth

The EL2244 and EL2444 have a gain-bandwidth product of

120MHz while using only 5.2mA of supply current per

amplifier. For gains greater than 4, their closed-loop -3dB

bandwidth is approximately equal to the gain-bandwidth

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

less than 4, higher-order poles in the amplifiers' transfer

function contribute to even higher closed loop bandwidths.

For example, the EL2244 and EL2444 have a -3dB

bandwidth of 120MHz at a gain of +1, dropping to 60MHz at

a gain of +2. It is important to note that the EL2244 and

EL2444 have 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

EL2244 and EL2444 in a gain of +1 only exhibit 1.0dB of

peaking with a 1k

Ω load.

Video Performance

An industry-standard method of measuring the video

distortion of components such as the EL2244 and EL2444 is

to measure the amount of differential gain (dG) and

differential phase (dP) that they introduce. To make these

device with 0V DC offset (0 IRE) at either 3.58MHz for NTSC

or 4.43MHz for PAL. A second measurement is then made

at 0.714V DC offset (100 IRE). Differential gain is a measure

of the change in amplitude of the sine wave, and is

measured in percent. Differential phase is a measure of the

change in phase, and is measured in degrees.

For signal transmission and distribution, a back-terminated

cable (75

Ω in series at the drive end, and 75Ω to ground at

the receiving end) is preferred since the impedance match at

both ends will absorb any reflections. However, when double

termination is used, the received signal is halved; therefore a

gain of 2 configuration is typically used to compensate for

the attenuation.

The EL2244 and EL2444 have been designed as an

economical solution for applications requiring low video

distortion. They have been thoroughly characterized for

video performance in the topology described above, and the

results have been included as typical dG and dP

specifications and as typical performance curves. In a gain

of +2, driving 150

Ω, with standard video test levels at the

input, the EL2244 and EL2444 exhibit dG and dP of only

0.04% and 0.15° at NTSC and PAL. Because dG and dP

can vary with different DC offsets, the video performance of

the EL2244 and EL2444 has been characterized over the

entire DC offset range from -0.714V to +0.714V. For more

information, refer to the curves of dG and dP vs DC Input

Offset.

Output Drive Capability

The EL2244 and EL2444 have been designed to drive low

load. This high output drive capability makes the EL2244

and EL2444 an ideal choice for RF, IF and video

applications. Furthermore, the current drive of the EL2244

and EL2444 remains a minimum of 35mA at low

temperatures.

Printed-Circuit Layout

The EL2244 and EL2444 are well behaved, and easy to

apply in most applications. However, a few simple

techniques will help assure rapid, high quality results. As

with any high-frequency device, good PCB layout is

necessary for optimum performance. Ground-plane

construction is highly recommended, as is good power

supply bypassing. A 0.1µF ceramic capacitor is

recommended for bypassing both supplies. Lead lengths

should be as short as possible, and bypass capacitors

should be as close to the device pins as possible. For good

AC performance, parasitic capacitances should be kept to a

minimum at both inputs and at the output. Resistor values

should be kept under 5k

Ω 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 their parasitic

inductance. Similarly, capacitors should be low-inductance

for best performance.

The EL2244 and EL2444 Macromodel

This macromodel has been developed to assist the user in

simulating the EL2244 and EL2444 with surrounding

circuitry. It has been developed for the PSPICE simulator

(copywritten by the Microsim Corporation), and may need to

be rearranged for other simulators. It approximates DC, AC,

and transient response for resistive loads, but does not

accurately model capacitive loading. This model is slightly

more complicated than the models used for low-frequency

op-amps, but it is much more accurate for AC analysis.

The model does not simulate these characteristics

accurately:

•Noise

•Settling time

• Non-linearities

• Temperature effects

• Manufacturing variations

•CMRR

• PSRR

EL2244, EL2444