LMH6574 datasheet(10/15 Pages) NSC

10 / 15 page

Application Notes

GENERAL INFORMATION

The LMH6574 is a high-speed 4:1 analog multiplexer, opti-

mized for very high speed and low distortion. With selectable

gain and excellent AC performance, the LMH6574 is ideally

suited for switching high resolution, presentation grade video

signals. The LMH6574 has no internal ground reference.

Single or split supply configurations are both possible. The

LMH6574 features very high speed channel switching and

disable times. When disabled the LMH6574 output is high

impedance making MUX expansion possible by combining

multiple devices. See “Multiplexer Expansion” section below.

VIDEO PERFORMANCE

The LMH6574 has been designed to provide excellent per-

formance with production quality video signals in a wide

variety of formats such as HDTV and High Resolution VGA.

Best performance will be obtained with back-terminated

loads. The back termination reduces reflections from the

transmission line and effectively masks transmission line

and other parasitic capacitances from the amplifier output

stage. Figure 1 shows a typical configuration for driving a

Ω. Cable. The output buffer is configured for a gain of 2,

so using back terminated loads will give a net gain of 1.

FEEDBACK RESISTOR SELECTION

The LMH6574 has a current feedback output buffer with gain

determined by external feedback (R

F) and gain set (RG)

resistors. With current feedback amplifiers, the closed loop

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FIGURE 1. Typical Application

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FIGURE 2. Suggested R

F vs. Gain

LMH6574 Datasheet(PDF) 10 Page - National Semiconductor (TI)