PRELIMINARY DATA SHEET
VDP 31xxB
2.8.4. Digital Brightness Adjustment
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.
The DC-level of the luminance signal can be adjusted by
adding an 8-bit number in the luminance signal path in
front of the softlimiter.
Part 2 has the same characteristics as part 1. The sub-
tracting part is also relative to the input signal, so the
total differential gain will become negative if the sum of
slope 1 and slope 2 is greater than 16 and the input sig-
nal is above the both tilt values (see characteristics).
Withacontrastadjustmentof32(gain+1)thesignalcan
be shifted by "100%. After the brightness addition, the
negative going signals are limited to zero. It is desirable
to keep a small positive offset with the signal to prevent
undershoots produced by the peaking from being cut.
The digital brightness adjustment is separate for main
and side picture.
Finally, the output signal of the soft limiter will be clipped
by a hard limiter adjustable from 256 to 511.
2.8.6. Chroma Input
2.8.5. Soft Limiter
The chroma input signal is a multiplexed C and C sig-
R
B
nal in 8-bit binary offset code. It can be switched be-
tween normal and inverted signal and between two’s
complement and binary offset code. The delay in re-
spect to the luminance input can be adjusted in 5 steps
within a range of "2 clock periods.
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
canbeadjustedbytheTVmanufactureraccordingtothe
CRT characteristics. All signals above this limit will be
‘soft’-clipped. A characteristic diagram of the soft limiter
is shown in Fig. 2–17. The total limiter consists of three
parts:
2.8.7. Chroma Interpolation
A linear phase interpolator is used to convert the chroma
sampling rate from 10.125 MHz (4:2:2) to 20.25 MHz
(4:4:4). All further processing is carried out at the full
sampling rate.
Part 1 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
Part 1
Part 2
Hard limiter
Output
511
Calculation Example for the
0
Softlimiter Input Amplitude.
(The real signal processing in
the limiter is 2 bit more than
described here)
2
slope 1 [0...15]
4
6
0
2
4
400
300
200
8
10
12
Y Input
16...235 (ITUR)
Black Level
Contrast
Dig. Brightness
BLE
16 (constant)
range= 256...511
6
8
63
20
off
off
14
10
12
14
slope 2 [0...15]
Peaking
Limiter input signal:
(Yin-Black Level)·Contr./32 + Brightn.
(235–16) · 63/32 + 20 = 451
100
0
tilt 1 [ 0...511]
tilt 2 [0...511]
Limiter Input
0
1023
400
500
900
100
200
300
600
700
800
Fig. 2–17: Characteristic of soft limiter a and b and hard limiter
Micronas
17
MICRONAS [ MICRONAS ]
