VDP3108B datasheet(17/72 Pages) MICRONAS

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PRELIMINARY DATA SHEET

VDP 31xxB

Micronas

2.8.4. Digital Brightness Adjustment

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.

With a contrast adjustment of 32 (gain

+1) the signal can

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.

2.8.5. 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. 2–17. The total limiter consists of three

parts:

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

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 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).

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

The chroma input signal is a multiplexed CR and CB sig-

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.

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.

Fig. 2–17: Characteristic of soft limiter a and b and hard limiter

Output

Limiter Input

slope 1 [0...15]

slope 2 [0...15]

Part 1

Part 2

Hard limiter

tilt 1 [ 0...511]

tilt 2 [0...511]

range= 256...511

511

1023

Calculation Example for the

Softlimiter Input Amplitude.

(The real signal processing in

the limiter is 2 bit more than

described here)

Y Input

16...235 (ITUR)

Contrast

Dig. Brightness

BLE

off

Peaking

off

Limiter input signal:

(Yin-Black Level)·Contr./32 + Brightn.

(235–16) · 63/32 + 20 = 451

Black Level

16 (constant)

100

200

300

400

500

600

700

800

900

100

200

300

400

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