sitic inductance, keep PC traces short and use surface-

mount components.

If input termination resistors and output back-termina-

tion resistors are used, they should be surface-mount

types, and should be placed as close to the IC pins as

possible.

Video Line Driver

The MAX4024/MAX4026 are well suited to drive short

coaxial transmission lines when the cable is terminated

at both ends (as shown in Figure 2a) where the fixed

gain of +2 compensates for the loss in the resistors.

The MAX4023/MAX4025 have settable gain to equalize

long cables. The MAX4023/MAX4025 allow adding

functions that normally require additional op amps. For

example, a cable driver can “boost” the high frequen-

cies for long runs, making the part perform multiple

functions. Figure 2b shows the “cable booster” using

the MAX4023/MAX4025.

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 is the

amplifier’s output impedance, which appears inductive

at high frequencies. This inductance forms an L-C reso-

nant circuit with the capacitive load, which causes

peaking in the frequency response and degrades the

amplifier’s phase margin.

Although the MAX4023–MAX4026 are optimized for AC

performance and are not designed to drive highly

capacitive loads, they are capable of driving up to

33pF without oscillations. However, some peaking may

occur in the frequency domain (Figure 3). To drive larg-

er capacitive loads or to reduce ringing, add an isola-

tion resistor between the amplifier’s output and the load

gain and the capacitive load (Figure 5). Also note that

the isolation resistor forms a divider that decreases the

voltage delivered to the load.

Triple and Quad, 2:1 Video Multiplexer-

Amplifiers with Fixed and Settable Gain

______________________________________________________________________________________

15

Figure 1. MAX4023/MAX4025 Noninverting Gain Configuration

75

Ω

75

Ω

75

Ω

OUT_

FB_

IN_A

IN_B

A/B

EN

75

Ω CABLE

75

Ω CABLE

75

Ω

75

Ω CABLE

MAX4023

MAX4025