9

Description of Operation and Application

Information

Product Description

The EL8102, EL8103 are wide bandwidth, single supply, low

power and rail-to-rail output voltage feedback operational

amplifiers. Both amplifiers are internally compensated for

closed loop gain of +1 of greater. Connected in voltage

follower mode and driving a 1k

Ω load, the EL8102, EL8103

have a -3dB bandwidth of 500MHz. Driving a 150

Ω load, the

bandwidth is about 350MHz while maintaining a 600V/us

slew rate. The EL8102 is available with a power down pin to

reduce power to 30µA typically while the amplifier is

disabled.

Input, Output and Supply Voltage Range

The EL8102, EL8103 have been designed to operate with a

single supply voltage from 3V to 5.0V. Split supplies can also

be used as long as their total voltage is within 3V to 5.0V.

The amplifiers have an input common mode voltage range

outside the above specified range, it will cause the output

signal to be distorted.

The output of the EL8102, EL8103 can swing rail to rail. As

the load resistance becomes lower, the ability to drive close

to each rail is reduced. For the load resistor 1k

Ω, the output

swing is about 4.9V at a 5V supply. For the load resistor

150

Ω, the output swing is about 4.6V.

Choice of Feedback Resistor and Gain Bandwidth

Product

For applications that require a gain of +1, no feedback

resistor is required. Just short the output pin to the inverting

input pin. For gains greater than +1, the feedback resistor

forms a pole with the parasitic capacitance at the inverting

input. As this pole becomes smaller, the amplifier’s phase

margin is reduced. This causes ringing in the time domain

some maximum value that should not be exceeded for

help to reduce the ringing and peaking at the expense of

reducing the bandwidth.

As far as the output stage of the amplifier is concerned, the

combination gets smaller, the bandwidth falls off.

is optimum. For the gains other than +1, optimum response

The EL8102, EL8103 have a gain bandwidth product of

200MHz. For gains

≥5, its bandwidth can be predicted by the

following equation:

Video Performance

For good video performance, an amplifier is required to

maintain the same output impedance and the same

frequency response as DC levels are changed at the output.

This is especially difficult when driving a standard video load

of 150

Ω, because the change in output current with DC level.

Special circuitry has been incorporated in the EL8102,

EL8103 to reduce the variation of the output impedance with

the current output. This results in dG and dP specifications

of 0.01% and 0.01

°, while driving 150Ω at a gain of 2. Driving

high impedance loads would give a similar or better dG and

dP performance.

Driving Capacitive Loads and Cables

The EL8102, EL8103 can drive 10pF loads in parallel with

1k

Ω with less than 5dB of peaking at gain of +1. If less

peaking is desired in applications, a small series resistor

(usually between 5

Ω to 50Ω) can be placed in series with the

FIGURE 29. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE

1

0.9

0.8

0.6

0.4

0.1

0

0

255075

100

150

AMBIENT TEMPERATURE (°C)

125

85

JEDEC JESD51-3 LOW EFFECTIVE

THERMAL CONDUCTIVITY TEST BOARD

0.2

0.7

0.3

0.5

625mW

SO8

SOT23-5/6

391mW

Gain

BW

×

200MHz

=

EL8102, EL8103