16

LT1675/LT1675-1

16751fs, sn16751 LT/TP 0199 4K • PRINTED IN USA

©LINEAR TECHNOLOGY CORPORATION 1998

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

RELATED PARTS

PART NUMBER

DESCRIPTION

COMMENTS

LT1203/LT1205

150MHz Video MUX

2-Input and 4-Input, 90dB Channel Separation, Wide Supply Range

LT1204

4-Input Video MUX with 75MHz Current Feedback Amp

Drives Cables, Adjustable Gain, 90dB Channel Separation

LT1260

Low Cost Dual and Triple 130MHz Current Feedback Amp

Drives Cables, Wide Supply Range, 0

µA Shutdown Current

with Shutdown

LT1398/LT1399

Low Cost Dual and Triple 300MHz Current Feedback Amp

Performance Upgrade for the LT1259/LT1260

with Shutdown

NTSC-Related Color Bar Generator

QA

QB

QC

CLK

CLR

LOAD

ENP

5V

ENT

A

5V

CLOCK IS

SUBCARRIER

× 4

DIVIDED BY 91

OR 157.343kHz

B

C

D

75

Ω

75

Ω

75

Ω

75

Ω

CABLE

CABLE

CABLE

SELECT

1675 TA04

ENABLE

COMPOSITE

SYNC

COMPOSITE

BLANKING

1k

1k

1k

75

Ω

LT1675

75

Ω

+1

+1

+2

+2

+2

+1

+1

+1

+1

6.04k

6.04k

R

6.04k

B

G

640

Ω

10k

–5V

–0.285V

74ACT04

74LS163

0

B

0.714V

0

R

0.714V

0

G

0.714V

An RGB color bar test pattern is easily generated by

dividing down a suitable clock. To form a stable pattern,

the clock must be synchronous with the horizontal scan

rate. Four times subcarrier, or 14.318MHz, is a readily

available frequency, which when divided by 91, gives

157.343KHz. Dividing this signal by two, four and eight,

gives the blue, read and green signals, respectively. This

timing gives eight bars including white and black that fill

the 52.6

µs active video time. The digital signals are run

through a 74ACT04 inverter because the CMOS output

swings rail-to-rail. The inverter output is scaled to make

video (0.714V peak, for NTSC-related RGB). The LT1675

drives the cable and adds sync to the RGB signals by

switching in –0.286V. If no sync is required, this voltage

can be set to zero and composite blanking can be used to

drive the select pin of the LT1675 in order to provide a

more precise blanking level.