LMH6574MA NSC [National Semiconductor], LMH6574MA Datasheet - Page 10

• Manufacturer Part Number: LMH6574MA
• Description: 4:1 High Speed Video Multiplexer
• Manufacturer: NSC [National Semiconductor]

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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
75Ω. Cable. The output buffer is configured for a gain of 2,
so using back terminated loads will give a net gain of 1.
FIGURE 1. Typical Application
10
FEEDBACK RESISTOR SELECTION
The LMH6574 has a current feedback output buffer with gain
determined by external feedback (R
resistors. With current feedback amplifiers, the closed loop
FIGURE 2. Suggested R
20119722
F
F
) and gain set (R
vs. Gain
20119732
G
)