appears inductive at high frequencies. This inductance

forms an L-C resonant circuit with the capacitive load,

which causes peaking in the frequency response and

degrades the amplifier’s phase margin.

The MAX4104/MAX4105/MAX4304/MAX4305 drive

capacitive loads up to 10pF without oscillation.

However, some peaking may occur in the frequency

domain (Figure 3). To drive larger capacitance loads or

to reduce ringing, add an isolation resistor between the

amplifier’s output and the load (Figure 4).

capacitive load (Figure 5). Figure 6 shows the

MAX4104/MAX4105/MAX4304/MAX4305 frequency

response with the isolation resistor and a capacitive

load. With higher capacitive values, bandwidth is domi-

bandwidth of the amplifier itself is much higher. Also

note that the isolation resistor forms a divider that

decreases the voltage delivered to the load.

Maxim’s High-Speed Evaluation Boards

The MAX4104 evaluation kit manual shows a suggest-

ed layout for Maxim’s high-speed, single-amplifier eval-

uation boards. This board was developed using the

techniques described previously (

see Layout and

Power-Supply Bypassing section). The smallest avail-

able surface-mount resistors were used for the feed-

back and back-termination resistors to minimize the

740MHz, Low-Noise, Low-Distortion

Op Amps in SOT23-5

______________________________________________________________________________________

11

Figure 3a. MAX4104 Frequency Response with Capacitive

Load and No Isolation Resistor

30

25

-20

100k

1M

10M

100M

1G

-10

-15

FREQUENCY (Hz)

0

-5

10

5

20

15

25

20

-25

100k

1M

10M

100M

1G

-15

-20

FREQUENCY (Hz)

-5

-10

5

0

15

10

Figure 3b. MAX4304 Frequency Response with Capacitive

Load and No Isolation Resistor

Figure 3d. MAX4305 Frequency Response with Capacitive

Load and No Isolation Resistor

Figure 3c. MAX4105 Frequency Response with Capacitive

Load and No Isolation Resistor

30

25

-20

100k

1M

10M

100M

1G

-10

-15

FREQUENCY (Hz)

0

-5

10

5

20

15

25

20

-25

100k

1M

10M

100M

1G

-15

-20

FREQUENCY (Hz)

-5

-10

5

0

15

10