Datasheet

16
LT1675/LT1675-1
16751fb
LT/LT 0605 REV B • PRINTED IN USA
© LINEAR TECHNOLOGY CORPORATION 1998
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone]
●
FAX: [phone]
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www.linear.com
TYPICAL APPLICATION
U
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
LT6555 650 MHz RGB Multiplexing Amplifier 2200V/µs Slew Rate, 2:1 Input MUX
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, 0µA 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
A5V
CLOCK IS
SUBCARRIER × 4
DIVIDED BY 91
OR 157.343kHz
B
C
D
75Ω
75Ω
75Ω
75Ω
CABLE
CABLE
CABLE
V
+
V
–
SELECT
1675 TA04
ENABLE
COMPOSITE
SYNC
COMPOSITE
BLANKING
1k
1k
1k
V
OUT BLUE
75Ω
LT1675
75Ω
V
OUT RED
V
OUT GREEN
+1
+1
+2
+2
+2
+1
+1
+1
+1
6.04k
6.04k R
6.04k
B
G
640Ω
10k
–5V
–0.285V
74ACT04
74LS163
WHITE
YELLOW
CYAN
GREEN
MAGENTA
RED
BLUE
BLACK
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, red and green signals, respectively. This
timing gives eight bars including white and black that fill
the 52.6µs 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.