EL2244, EL2444

FN7059 Rev 2.00

Page 9 of 11

May 16, 2005

input voltage range reaches 4.2V, and output voltage range

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

 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 measurements, a

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

 in series at the drive end, and 75 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

, 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

 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 and EL244C Macromodel

* Connections: +input

*

|

-input