MAX496 データシートの表示（PDF） - Maxim Integrated

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MAX496

375MHz Quad Closed-Loop Video Buffers, AV = +1 and +2

Maxim Integrated 

375MHz Quad Closed-Loop

Video Buffers, AV = +1 and +2

MAX496/MAX497

MAX496/MAX497

50Ω

VIN = 4Vp-p,

f = 10MHz,

50Ω

RS = 75Ω

100Ω

100Ω

50Ω

50Ω

100Ω

100Ω

50Ω

100Ω

50Ω

100Ω

50Ω

100Ω

VIN = 4Vp-p,

f = 10MHz,

50Ω

100Ω

RS = 75Ω

a) ADJACENT CHANNEL

Figure 4. Crosstalk: a) Adjacent Channel; b) All-Hostile

b) ALL-HOSTILE

Total Noise

The MAX496/MAX497’s low input current noise of

2pA/√Hz and voltage noise of 5.6nV/√Hz provide for

lower total noise compared to typical current-mode-

feedback amplifiers, which usually have significantly

higher input current noise. The input current noise mul-

tiplied by the feedback resistor is the dominant noise

source of current-mode-feedback amplifiers.

Differential Gain and Phase Errors

Differential gain and phase errors are critical specifica-

tions for a buffer in composite (NTSC, PAL, SECAM) video

applications, because these errors correspond directly to

color changes in the displayed picture of composite video

systems. The MAX496/MAX497’s ultra-low differential gain

and phase errors (0.01%/ 0.01°) make them ideal in

broadcast-quality composite video applications.

Distribution Amplifier

The circuit in Figure 3 is a one-to-four distribution amplifier

using a single MAX496 or MAX497 IC. A one-to-eight dis-

tribution amplifier can be implemented with a MAX496 or

MAX497 by driving an additional cable from each of the

four outputs. When driving more than four outputs from a

single device, see the Continuous Power Dissipation

specifications in the Absolute Maximum Ratings.

Coaxial Cable Drivers

High-speed performance, excellent output current

capability, and an internally fixed gain of +2 make the

MAX497 ideal for driving back-terminated 50Ω or 75Ω

coaxial cables to ±2.8V.

In a typical application, the MAX497 drives a back-ter-

minated 75Ω video cable (Figure 1). The back-termina-

tion resistor (at the MAX497’s output) matches the

impedance of the cable’s driven end to the cable’s

impedance, to eliminate signal reflections. This, along

with the load-termination resistor, forms a voltage

divider with the load impedance, which attenuates the

signal at the cable output by one-half. The MAX497

operates with an internal +2V/V closed-loop gain to pro-

vide unity gain at the cable’s output.

Capacitive Load Driving

In most amplifier circuits, driving large capacitive loads

increases the likelihood of oscillation. This is especially

true for circuits with high loop gains, such as voltage

followers. The amplifier’s output resistance and the

capacitive load form an RC filter that adds a pole to the

loop response. If the pole frequency is low enough (as

when driving a large capacitive load), the circuit phase

margin is degraded and oscillation may occur.

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