High-Speed, Low-Power, Single-Supply,

Multichannel, Video Multiplexer-Amplifiers

______________________________________________________________________________________

15

Driving Capacitive Loads

A correctly terminated transmission line is purely resis-

tive and presents no capacitive load to the amplifier.

Reactive loads decrease phase margin and may pro-

duce excessive ringing and oscillation (see

Typical

Operating Characteristics).

Another concern when driving capacitive loads origi-

nates from the amplifier’s output impedance, which

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.

Although the MAX4310–MAX4315 are optimized for AC

performance and are not designed to drive highly capaci-

tive loads, they are capable of driving up to 20pF without

oscillations. However, some peaking may occur in the fre-

quency domain (Figure 6). To drive larger capacitive

loads or to reduce ringing, add an isolation resistor

between the amplifier’s output and the load (Figure 7).

capacitive load (Figure 8). Figure 9 shows the

MAX4310–MAX4315 frequency response with the isola-

tion resistor and a capacitive load. With higher capaci-

tive values, bandwidth is dominated by the RC network

itself is much higher. Also note that the isolation resistor

forms a divider that decreases the voltage delivered to

the load.

Figure 10. High-Speed EV Board Layout—Component Side

Figure 11. High-Speed EV Board Layout—Solder Side

1

0

1

0

0

1

CHANNEL SELECTED

A2

SHDN

1

0

3

2

0

1

0

0

A1

1

1

0

X

None, High-Z Output

X

1

1

4

1

1

6

5

1

1

0

1

0

1

1

7

1

1

0

A0

1

0

X

0

0

1

1

1

—

1

0

—

1

CHANNEL SELECTED

A2

SHDN

1

—

3

2

—

1

—

—

A1

1

1

0

—

None, High-Z Output

—

1

0

A0

1

0

X

1

—

1

0

—

1

CHANNEL SELECTED

A2

SHDN

0

0

A1

0

—

None, High-Z Output

X

1

0

A0

X

MAX4310/MAX4313

MAX4311/MAX4314

MAX4312/MAX4315

Table 2. Input Control Logic