MAX7474 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX7474

Adaptive Equalizer for Video Over Twisted Pair

Maxim Integrated 

Adaptive Equalizer for

Video Over Twisted Pair

PIN

1, 2, 3,

5, 10, 13

4, 9

6

7

8

11

12

14

15

16

NAME

GND

VCC

LOB

BPLVL

OUT

FEQ0

FEQ1

INP

INN

LOS

FUNCTION

Pin Description

Ground. Connect all GND terminals together.

Power-Supply Input. Connect a +4.75V to +5.25V supply to VCC. Connect both VCC inputs together.

Bypass each VCC input with a 0.1µF capacitor to GND as close as possible to the device.

Loss-of-Burst Logic Output. LOB goes high when the output color burst goes below the LOB threshold

(VLOB) for 32 consecutive horizontal lines when the equalizer is at its maximum gain. LOB goes low

when the output color burst exceeds VLOB for 32 consecutive horizontal lines. When LOB is active, the

device enters the fixed equalization mode. LOB is valid only when LOS is low.

Back-Porch Level Input. The voltage applied to BPLVL sets the output back-porch voltage level.

Composite Video Output

Fixed-Cable Equalization inputs. FEQ0 and FEQ1 set the fixed equalization level. See Table 1.

Noninverted Video Input. AC-couple video signal with a 0.022µF capacitor.

Inverted Video Input. AC-couple video signal with a 0.022µF capacitor.

Loss-of-Sync Logic Output. LOS goes high when the input sync amplitude goes below the loss-of-sync

threshold (VLOS) for 32 consecutive horizontal lines. LOS is pulled low when the input sync amplitude

exceeds VLOS for 32 consecutive horizontal lines. When LOS is active, the output enters a high-

impedance state.

Detailed Description

The MAX7474 compensates for cable losses that

occur when transmitting a composite video signal over

unshielded twisted-pair cable (see the Typical

Application Circuit). The device automatically adapts

to cable length by monitoring the sync and color-burst

amplitudes of the color video signal at the output

(OUT) and adjusting the gains accordingly. Video sig-

nals without burst are automatically detected and a

user-selectable fixed equalization is applied to the sig-

nal. The MAX7474 provides full equalization up to

300m of Category 5e cable and greatly improves per-

formance up to 600m.

The MAX7474 accepts differential video input signals in

NTSC or PAL standards. The MAX7474 includes an

output unity-gain video driver and adjustable back-

porch DC level. The device also features LOS and LOB

logic outputs.

Video Input

The MAX7474 accepts a differential video input with a

maximum 2.4VP-P voltage swing. A twisted-pair cable

carries the differential video signal to the positive (INP)

and negative (INN) inputs, which are AC-coupled with

0.022µF capacitors. Each input is internally clamped to

a DC level (see the Input Clamp section).

Input Clamp

The MAX7474 clamps the sync tip of the input signal to

internally set DC levels effectively correcting, on a line-

by-line basis, any shift in the sync-tip level of the input

video signal. The sync-tip of the positive video input

signal (VINP) is clamped to typically 2.0V and the nega-

tive video input signal (VINN) is clamped to typically

3.2V. The input clamp enables capacitive coupling of

the input, permitting a large common-mode DC differ-

ence between the line driver (camera) and the device.

Adaptive Equalizer

The adaptive equalizer in the MAX7474 provides the

appropriate inverse frequency response needed to

compensate for UTP cable loss. The equalizer adjusts

the low-frequency amplitude and chroma amplitude of

the input CVBS signal. The low-frequency component

of the CVBS is adjusted according to the feedback

information obtained from the internal automatic gain-

control (AGC) circuit, which monitors the sync pulse

amplitude of the output signal (see the Automatic Gain

Control (AGC) section). The chroma gain of the video

signal is adjusted according to the feedback informa-

tion obtained from the internal automatic equalization

control circuit, which monitors the color-burst amplitude

of the output signal (see the Automatic Equalization

Control (AEQ) section).

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