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

Multichannel, Video Multiplexer-Amplifiers

12

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_______________Detailed Description

The MAX4310/MAX4311/MAX4312 combine 2-channel,

4-channel, or 8-channel multiplexers, respectively, with

an adjustable-gain output amplifier optimized for

closed-loop gains of +1V/V (0dB) or greater. The

MAX4313/MAX4314/MAX4315 combine 2-channel, 4-

channel, or 8-channel multiplexers, respectively, with a

+2V/V (6dB) fixed-gain amplifier, optimized for driving

back-terminated cables. These devices operate from a

single supply voltage of +4V to +10.5V, or from dual

supplies of ±2V to ±5.25V. The outputs may be placed

in a high-impedance state and the supply current mini-

mized by forcing the SHDN pin low. The input multi-

plexers feature short 40ns channel-switching times and

small 10mVp-p switching transients. The input capaci-

tance remains constant at 1pF whether the channel is

on or off, providing a predictable input impedance to

the signal source. These devices feature single-supply,

rail-to-rail, voltage-feedback output amplifiers that

achieve up to 540V/µs slew rates and up to 345MHz -3dB

bandwidths. These devices also feature excellent har-

monic distortion and differential gain/phase perfor-

mance.

__________Applications Information

Rail-to-Rail Outputs, Ground-Sensing Input

The input common-mode range extends from the nega-

mode rejection. Beyond this range, multiplexer

switching times may increase and the amplifier output

is a nonlinear function of the input, but does not under-

go phase reversal or latchup.

Ω load. With a 150Ω load to ground, the

the supply rail. Local feedback around the output stage

ensures low open-loop output impedance to reduce

gain sensitivity to load variations. This feedback also

produces demand-driven bias current to the output

transistors for ±95mA drive capability while constrain-

ing total supply current to only 6.1mA.

Feedback and Gain Resistor Selection

(MAX4310/MAX4311/MAX4312)

Select the MAX4310/MAX4311/MAX4312 gain-setting

tion. Large resistor values increase voltage noise and

interact with the amplifier’s input and PC board capaci-

tance. This can generate undesirable poles and zeros,

and can decrease bandwidth or cause oscillations. For

Ω resistors, combined with 2pF of input

capacitance and 1pF of PC board capacitance, causes

a pole at 159MHz. Since this pole is within the amplifier

bandwidth, it jeopardizes stability. Reducing the 1k

Ω

resistors to 100

Ω extends the pole frequency to

1.59GHz, but could limit output swing by adding 200

Ω in

parallel with the amplifier’s load resistor.

MAX4310/MAX4311/MAX4312 when operating in the

noninverting configuration (shown in Figure 1). These

values provide optimal AC response using surface-

mount resistors and good layout techniques, as dis-

cussed in the

Layout and Power-Supply Bypassing

section.

Stray capacitance at the FB pin causes feedback resis-

tor decoupling and produces peaking in the frequency-

response curve. Keep the capacitance at FB as low as

possible by using surface-mount resistors and by

avoiding the use of a ground plane beneath or beside

these resistors and the FB pin. Some capacitance is

unavoidable; if necessary, its effects can be neutralized

tency over a wide range of production lots.

MAX4310

75

Ω

8

OUT

7

FB

IN0

IN1

4

5

1

A0

75

Ω

75

Ω CABLE

75

Ω

75

Ω

75

Ω CABLE

75

Ω CABLE

Figure 1. MAX4310 Noninverting Gain Configuration

Table 1. Bandwidth and Gain with

Suggested Gain-Setting Resistors

(MAX4310/MAX4311/MAX4312)

GAIN

(V/V)

GAIN

(dB)

(

Ω)

(

Ω)

-3dB BW

(MHz)

0.1dB BW

(MHz)

80

280

500

∞

500

0

6

0

1

2

5

14

500

120

4

20

2

10

56

500

20

10

30

60