MAX9541(2009) データシートの表示（PDF） - Maxim Integrated

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MAX9541
(Rev.:2009)

Quadruple, 2:1, Mux Amplifiers for Standard-Definition and VGA Signals

Maxim Integrated 

Quadruple, 2:1, Mux Amplifiers for

Standard-Definition and VGA Signals

Operating Modes

A/B controls whether Video Input A or Video Input B is

selected. See Table 1.

SHDN controls whether the device is on or off. See

Table 2. In shutdown, the outputs are in high imped-

ance.

Input

Each video source can provide up to four video signals.

Every video signal must be AC-coupled to the

MAX9541/MAX9542 through 0.1µF capacitors. The

MAX9541/MAX9542 have sync-tip clamps and bias cir-

cuits to restore the DC level of the video signal after the

input coupling capacitor. When a video input is select-

ed, the input has a sync-tip clamp, which accepts

video signals that have sync pulses or that reach their

minimum level during sync. Composite video with

blanking and sync (CVBS) is an example of a video sig-

nal with sync pulses. The red, green, and blue signals

in an RGBS signal set are examples of signals that

return to their blank level during sync. The sync-tip volt-

age is internally set to 300mV.

When a video input is not selected, the inputs to the

MAX9541/MAX9542 do not distort the video signal in

case the video source is driving video signals to anoth-

er video circuit such as a video multiplexer. The inputs

are biased at VDD/3, which is sufficiently above ground

so that the ESD diodes never forward bias as the video

signal changes. The input resistance is 220kΩ, which

presents negligible loading on the video current DAC.

The sole exception to this condition is IN3A, in which

the input circuit is always a sync-tip clamp. Table 3

summarizes which input circuit is active, dependent

upon A/B.

In shutdown mode (SHDN = LOW), a bias circuit is

active on every input.

Table 1. A/B Logic

LOGIC STATE

Low

High

Table 2. SHDN Logic

MODE

Video Input A

Video Input B

LOGIC STATE

Low

High

MODE

Off

On

Multiplexer

The MAX9541/MAX9542 have quadruple 2:1 multiplex-

ers to select between either Video Input A or Video

Input B as the source of the video signal. When A/B is

connected to GND, Video Input A is the video source.

When A/B is connected to VDD, Video Input B is the

video source.

Video Filter

The MAX9541 filter features ±1dB passband out to

9.5MHz and 47dB attenuation at 27MHz, making the fil-

ter suitable for standard-definition video signals from all

sources (e.g., broadcast and DVD). Broadcast video

signals are channel limited: NTSC signals have 4.2MHz

bandwidth, and PAL signals have 5MHz bandwidth.

Video signals from a DVD player, however, are not

channel limited; so the bandwidth of DVD video signals

can approach the Nyquist limit of 6.75MHz.

Recommendation: ITU-R BT.601-5 specifies 13.5MHz

as the sampling rate for standard-definition video.

Therefore, the maximum bandwidth of the signal is

6.75MHz. To ease the filtering requirements, most mod-

ern video systems oversample by two times, clocking

the video current DAC at 27MHz.

The MAX9542 does not have a filter.

Table 3. Input Circuit of Input as Determined by State of A/B (SHDN = HIGH)

INPUT

IN0A

IN1A

IN2A

IN3A

IN0B

IN1B

IN2B

IN3B

INPUT CIRCUIT

A/B = LOW

Sync-tip clamp

Sync-tip clamp

Sync-tip clamp

Sync-tip clamp

Bias

Bias

Bias

Bias

INPUT CIRCUIT

A/B = HIGH

Bias

Bias

Bias

Sync-tip clamp

Sync-tip clamp

Sync-tip clamp

Sync-tip clamp

Sync-tip clamp

12 ______________________________________________________________________________________

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