The MAX496/MAX497 drive capacitive loads up to 75pF

without sustained oscillation, although some peaking

may occur. When driving larger capacitive loads, or to

the output and the capacitive load (Figures 5a–5d).

Grounding and Layout

The MAX496/MAX497 bandwidths are in the RF fre-

quency range. Depending on the size of the PC board

used and the frequency of operation, it may be neces-

sary to use Micro-strip or Stripline techniques.

To realize the full AC performance of these high-speed

buffers, pay careful attention to power-supply bypassing

and board layout. The PC board should have at least two

layers (wire-wrap boards are too inductive, bread boards

are too capacitive), with one side a signal layer and the

other a large, low-impedance ground plane. With multilay-

er boards, locate the ground plane on the layer that is not

dedicated to a specific signal trace. The ground plane

should be as free from voids as possible. Connect all

ground pins to the ground plane.

Connect both positive power-supply pins together and

bypass with a 0.10µF ceramic capacitor at each power

supply pin, as close to the device as possible. Repeat

the same for the negative power-supply pins. The

capacitor lead lengths should be as short as possible

to minimize lead inductance; surface-mount chip

capacitors are ideal. A large-value (4.7µF or greater)

tantalum or electrolytic bypass capacitor on each sup-

ply may be required for high-current loads. The location

of this capacitor is not critical.

The MAX496/MAX497’s analog input pins are isolated

with ground pins to minimize parasitic coupling, which can

degrade crosstalk and/or amplifier stability. Keep signal

paths as short as possible to minimize inductance. Ensure

that all input channel traces are the same length to main-

tain the phase relationship between the four channels. To

further reduce crosstalk, connect the coaxial-cable shield

to the ground side of the 75

Ω terminating resistor at the

ground plane, and terminate all unused inputs ground and

outputs with a 100

Ω or 150Ω resistor to ground.

375MHz Quad Closed-Loop

______________________________________________________________________________________

11

1M

10M

1G

-12

-10

-8

-6

-4

-2

0

2

4

6

8

FREQUENCY (Hz)

100M

Figure 5a. MAX496 Small-Signal Gain vs. Frequency and Load

1M

10M

1G

-30

-25

-20

-15

-10

-5

0

5

10

15

20

FREQUENCY (Hz)

100M

1M

10M

1G

-30

-25

-20

-15

-10

-5

0

5

10

15

20

FREQUENCY (Hz)

100M

Figure 5c. MAX496 Small-Signal Gain vs. Frequency and Load

1M

10M

1G

-5

-4

-3

-2

-1

0

1

2

3

4

5

FREQUENCY (Hz)

* -3dB ATTENUATION DUE

100M

Figure 5b. MAX496 Small-Signal Gain vs. Frequency and

Figure 5d. MAX496 Small-Signal Gain vs. Frequency and