MAX11503 データシートの表示（PDF） - Maxim Integrated

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MAX11503

Video Y/C Summer with Driver and Chroma Mute

Maxim Integrated 

Video Y/C Summer with

Driver and Chroma Mute

Pin Description

PIN

NAME

1

YIN Luma Input

2

GND Ground

3

OUT Video Out

FUNCTION

4

SAG

Sag Correction Input. Connect to OUT when AC- or DC-coupling video output. See Figure 1 to determine

capacitor value and circuit.

5

VCC Power Supply. Bypass to GND with 0.1µF and 1µF capacitors.

6

PSAVE Active-Low Power-Save Logic Input. Connect PSAVE to VCC for normal operation. Drive low to put device

into a low-power consumption mode.

7

CMUTE

Chroma Mute Logic Input. Connect CMUTE to ground for normal operation. Drive high to disable the

chroma buffer.

8

CIN Chroma Input

EP

—

Exposed Pad. Connect EP to ground.

Detailed Description

The MAX11503 is a low-power video amplifier with a

Y/C summer and chroma mute. The device accepts an

S-video or Y/C input and sums the luma (Y) and chroma

(C) signals into a composite CVBS signal which can be

connected directly to a TV monitor. The MAX11503 drives

two terminated 75Ω video coax cables.

The MAX11503 features chroma mute, power save, and

SAG correction. Chroma mute disables the chroma

buffer. If the device is used to combine Y and C signals

in a camera application, chroma mute may be used in

low-light situations. This removes all chroma including

burst which causes a downstream composite video

decoder to interpret the video signal as luminance only,

thus improving image quality. Power-save puts the

device into a low-power consumption mode. SAG

correction allows small output capacitors to be used

in AC-coupled output applications.

The MAX11503 has a transparent clamp at YIN, allow-

ing the luma input to be AC- or DC-coupled. If the luma

input is DC-coupled, the sync tip must be at ground

and the video signal must be 1VP-P. For low-supply

voltages, ensure that the DC level of the input is low

enough to avoid clipping at the output. If the luma input

is AC-coupled, the clamp adjusts the luma signal’s

sync tip to ground at YIN. Use an AC-coupling capacitor

of 0.1µF.

The MAX11503 has an internal AC-coupling capacitor

at CIN, allowing the chroma input to be coupled directly

to CIN.

Chroma Mute

In applications using cameras that output composite

video, the video is always decoded by a downstream

composite decoder in a monitor or for further video

processing.

In low-light conditions, the camera video signal

becomes noisy. The high-frequency (less visible mono-

chrome) noise from the camera is transformed to low-

frequency highly visible colored noise by the normal

encode and decode blocks of composite video pro-

cessing. This is caused when the chroma information is

encoded onto a high-frequency subcarrier, mixed with

the luminance and the decoded. First, high-frequency

noise near the color subcarrier is down-converted to

low-frequency noise. Second, chroma separation by

comb filtering removes luminance noise, but correlates

the noise in phase with the chroma to become vertical

lines. These two effects cause highly visible and objec-

tional color noise. Hence, using a purely monochrome

signal is better looking than a color signal.

When pulled high, the chroma mute input disables all

chroma and burst and the device outputs a mono-

chrome video signal. This causes the downstream

decoder to recognize the video signal as monochrome.

Power-Save

Asserting PSAVE logic low puts the device into a

power-down mode, reducing the supply current to

0.5µA and minimizing power consumption. Connect

PSAVE to VCC for normal operation.

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