2.1.5. Soft Limiter
The dynamic range of the processed luma signal must
be limited to prevent the CRT from overload. An appro-
priate headroom for contrast, peaking, and brightness
can be adjusted by the TV manufacturer according to
the CRT characteristics. All signals above this limit will
be “soft”-clipped. A characteristic diagram of the soft
limiter is shown in Fig. 2–3. The total limiter consists of
three parts:
Part A includes adjustable tilt point and gain. The gain
before the tilt value is 1. Above the tilt value, a part
(0…15/16) of the input signal is subtracted from the
input signal itself. Therefore, the gain is adjustable
from 16/16 to 1/16, when the slope value varies from 0
to 15. The tilt value can be adjusted from 0 to 511.
Part B has the same characteristics as part A. The
subtracting part is also relative to the input signal, so
the total differential gain will become negative if the
sum of slope A and slope B is greater than 16 and the
input signal is above the both tilt values (see character-
istics).
Finally, the output signal of the soft limiter will be
clipped by a hard limiter adjustable from 256 to 511.
ADVANCE INFORMATION
Table 2–2:
4:1:1 Chroma format
Pin Name
1
C7
C6
C5
C4
C
b17
C
b16
C
r17
C
r16
Pixel Number
2
C
b15
C
b14
C
r15
C
r14
3
C
b13
C
b12
C
r13
C
r12
4
C
b11
C
b10
C
r11
C
r10
Note:
C
xy
; x = pixel number, y = bit number
Table 2–3:
4:2:2 Chroma format
Pin Name
1
C7
C6
C5
C
b17
C
b16
C
b15
C
b14
C
b13
C
b12
C
b11
C
b10
Pixel Number
2
C
r17
C
r16
C
r15
C
r14
C
r13
C
r12
C
r11
C
r10
3
C
b37
C
b36
C
b35
C
b34
C
b33
C
b32
C
b31
C
b30
4
C
r37
C
r36
C
r35
C
r34
C
r33
C
r32
C
r31
C
r30
2.1.6. Chroma Input
The chroma input signal can either be YC
r
C
b
in 4:1:1
or in 4:2:2 format. For the digital signal processing, the
time-multiplexed chroma samples will be demulti-
plexed and synchronized with the signal at the HS pin.
The input formatter accepts either two’s complement
or binary offset code. Also, the delay can be adjusted
within a range of
±
2 input clocks relative to the luma
signal; this doesn’t affect the chroma multiplex.
C4
C3
C2
C1
C0
Note:
C
xy
; x = pixel number, y = bit number
Output
511
Part A
Slope A [0...15]
Part B
0
2
4
6
8
10
12
Hard limiter
Calculation example for the soft-
limiter input amplitude.
400
0
2
4
6
8
10
12
14
Y Input
16...235 (ITU-R 601)
16 (constant)
63
20
off
300
Range= 256...511 Black Level
Contrast
14
Dig. Brightness
Peaking
Slope B [0...15]
200
Limiter input signal:
100
Tilt A [ 0...511]
0
0
100
200
300
400
500
600
700
800
900
Tilt B [0...511]
(235-16)
×
63/32 + 20 = 451
Limiter Input
1023
(Yin-black level)
×
CTM/32‘+BRM
Fig. 2–3:
Characteristics of soft limiter A and B and hard limiter
8
Micronas
MICRONAS [ MICRONAS ]
