350MHz/250MHz, 2-Channel

Video Multiplexer-Amplifiers

10

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_______________Detailed Description

The MAX4158/MAX4159 are optimized for closed-loop

MAX4259 are optimized for closed-loop gains of 2V/V

(6dB) or greater. These low-power, high-speed, cur-

rent-mode feedback amplifiers operate from ±5V sup-

plies. They drive video loads (including 50

Ω and 75Ω

cables) with excellent distortion characteristics.

Differential gain and phase errors are 0.01%/0.01° for

MAX4158/MAX4159 and 0.01%/0.02° for MAX4258/

MAX4259, respectively.

The input multiplexers feature very short switching

times and small switching transients. They also have

high input resistance and constant input capacitance,

so overall input impedance can be set by external input

terminating resistors. Each video input is isolated by an

AC-ground pin, which reduces channel-to-channel

capacitance and minimizes crosstalk.

The MAX4159/MAX4259 have address latching and an

output enable function that places the output in a high-

impedance state. These functions allow multiple

mux/amps to be paralleled together to form larger

switching arrays.

________________________Truth Tables

Input Control Logic

X = Don’t Care

MAX4159/MAX4259

Output Control Logic

All logic levels (EN, LE, and A0) default low (0) if left open circuit.

Output disable is completely independent of input address and

latch.

__________Applications Information

Theory of Operation

Since the MAX4158/MAX4159/MAX4258/MAX4259 are

current-mode feedback amplifiers, their open-loop

transfer function is expressed as a transimpedance,

open-loop transimpedance is similar to the open-loop

gain of a voltage-mode feedback amplifier. That is, it

has a large DC value and decreases at approximately

6dB per octave at high frequency.

Analyzing the current-mode feedback amplifier in a

gain configuration (Figure 1) yields the following trans-

fer function:

tional voltage-mode feedback amplifiers, the closed-

loop bandwidth is essentially independent of

closed-loop gain. Note also that at low frequencies,

Layout and Power-Supply Bypassing

The MAX4158/MAX4159/MAX4258/MAX4259 have

extremely high bandwidth, and consequently require

careful board layout, including the possible use of con-

stant-impedance microstrip or stripline techniques.

MAX4158

MAX4159

MAX4258

MAX4259

FB

OUT

+1

IN0

IN1

+1

Figure 1. Current-Mode Feedback Amplifier

On

AMPLIFIER

OUTPUT

Off

0

Output on

LOGIC

INPUT

EN

N )

FUNCTION

1

Output off; high impedance

LE

A0

AMPLIFIER

INPUT

LOGIC

INPUTS

FUNCTION

[LAST]

1

X

Channel addresses latched;

retains last input address.

IN1

0

1

Channel 1 selected

IN0

0

0

Channel 0 selected