AD8024

–9–

REV. B

General

The AD8024 is a wide bandwidth, quad video amplifier. It offers a

high level of performance on 16 mA total quiescent supply cur-

rent for closed-loop gains of

±1 or greater.

Bandwidth up to 380 MHz, low differential gain and phase errors,

and high output current make the AD8024 an efficient video

amplifier.

The AD8024’s wide phase margin and high output current make it

an excellent choice when driving any capacitive load.

Choice of Feedback Resistor

Because it is a current feedback amplifier, the closed-loop

bandwidth of the AD8024 may be customized with the feed-

back resistor.

A larger feedback resistor reduces peaking and increases the

phase margin at the expense of reduced bandwidth. A smaller

feedback resistor increases bandwidth at the expense of increased

peaking and reduced phase margin.

The closed-loop bandwidth is affected by attenuation due to the

finite output resistance. The open-loop output resistance of

≈6 Ω

reduces the bandwidth somewhat when driving load resistors less

than

≈150 Ω. The bandwidth will be ≈10% greater for load resis-

tance above a few hundred ohms.

The value of the feedback resistor is not critical unless maintaining

the widest or flattest frequency response is desired. Table I shows

the bandwidth at different supply voltages for some useful closed-

loop gains when driving a 150

Ω load. The recommended resistors

are for the widest bandwidth with less than 2 dB peaking.

Table I. –3 dB Bandwidth vs. Closed-Loop Gain Resistor,

Gain

BW – MHz

±7.5

+1

5000

350

+2

750

275

+10

400

105

–1

750

165

±12

+1

8000

380

+10

215

150

–1

750

95

±2.5

+2

1125

125

Driving Capacitive Loads

When used in combination with the appropriate feedback resistor,

the AD8024 will drive any load capacitance without oscillation.

In accordance with the general rule for current feedback ampli-

fiers, increased load capacitance requires the use of a higher

feedback resistor for stable operation.

Due to the high open-loop transresistance and low inverting

input current of the AD8024, large feedback resistors do not

create large closed-loop gain errors. In addition, the high output

current allows rapid voltage slewing on large load capacitors.

For wide bandwidth and clean pulse response, an additional

small series output resistor of about 10

Ω is recommended.

–

+

AD8024

1.0 F

0.1 F

1.0 F

0.1 F

Figure 31. Circuit for Driving a Capacitive Load

1V

2V

Figure 32. Pulse Response Driving a Large Load

Ω,