VDP313XY datasheet(17/76 Pages) MICRONAS

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ADVANCE INFORMATION

VDP 313xY

Micronas

2.10.4.Digital Brightness Adjustment

The DC-level of the luminance signal can be adjusted

by adding/subtracting an 8-bit number in the lumi-

nance signal path in front of the softlimiter.

After the brightness addition, the negative going sig-

nals 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.

2.10.5.Soft Limiter

The dynamic range of the processed luminance signal

must be limited to prevent the CRT from overload. An

appropriate headroom for contrast, peaking and bright-

ness can be adjusted by the TV manufacturer accord-

ing to the CRT characteristics. All signals above this

limit will be soft-clipped. A characteristic diagram of the

soft limiter is shown in Fig. 2–14. The total limiter con-

sists of three parts:

1. 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 adjust-

able 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.

2. Part 2 has the same characteristics as part 1. The

subtracting 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 signal is above the both tilt values (see

characteristics).

3. Finally, the output signal of the soft limiter will be

clipped by a hard limiter adjustable from 256 to 511.

2.10.6.Chrominance Interpolation

A linear phase interpolator is used to convert the

chrominance 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. 2–14: Characteristic of soft limiter a and b and hard limiter

100

200

300

400

500

600

700

800

900

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)

Black Level

16 (constant)

Contrast

Dig. Brightness

BLE

off

Peaking

off

Limiter input signal:

(Yin-Black Level)

⋅Contr./32 + Brightn.

(235-16)

⋅ 63/32 + 20 = 451

slope 2

[0..15]

Hard limiter

range=

256..511

slope 1

[0..15]

tilt 1 [ 0..511]

tilt 2 [ 0..511]

100

200

300

400

511

Output

Part 1

Part 2

Limiter Input

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