9.
Video amplifier system with on-screen display
LM1281 (U201)
Outstanding features:
* Three-channel video amplifier bandwidth 85 MHz @ -3 dB (4 Vp-p output)
* OSD TTL input, bandwidth 50 MHz
* High-speed video/OSD changeover
* High impedance DC contrast control above the 0-4V, 40dB range
* High impedance DC OSD contrast control above the 0-4V, 40dB range
BLOCK AND CONNECTION DIAGRAM
Red OSD Input
Green OSD Input
Blue OSD Input
Video/OSD Switch
Red Video In
V
CC1
Ground
Green Video In
V
CC1
Ground
Blue Video In
V
REF
Video Contrast
OSD Contrast
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
Red Drive Adjust
Green Drive Adjust
Blue Drive Adjust
RGB Cutoff Adjust
Red Clamp Cap
Red Video Out
V
CC2
Ground
Green Video Out
Green Clamp Cap
Blue Video Out
Blue Clamp Cap
Blank Gate
Clamp Gate
Contrast
Attenuation
Contrast
Attenuation
Contrast
Attenuation
Drive
Attenuation
Contrast
Attenuation
Contrast
Attenuation
Top View
-A1
-A1
-A1
-A2
-A2
-A2
Description of the functions
Figure 1 shows the block diagram of LM1281, in conformity with the pin layout of the IC.
Every channel accepts both the video signal and the OSD signal at the input anplifier (A1).
Also the video/OSD changeover signal passes either the video signal or the OSD signal through LM1281,
or is connected with the input amplifier for control purposes. The next contrast adjustment block is a drive
adjustment type one.
The reference level for the DC return circuit is set by means of the RGB cutoff adjustment pin (PIN 25).
Attention must be paid to the fact that the blank clamp gate is active when it is stuck at the LOW state.
Under ordinary circumstances, these pins are controlled by means of the standard TTL signal.
65
Summary of Contents for Diamand Scan 71
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