VDP3108B datasheet(18/72 Pages) MICRONAS

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PRELIMINARY DATA SHEET

VDP 31xxB

Micronas

2.8.8. Chroma Transient Improvement

The intention of this block is to enhance the chroma

resolution. A correction signal is calculated by differenti-

ation of the color difference signals. The differentiation

can be selected according to the signal bandwidth, e.g.

for PAL/NTSC/SECAM or digital component signals,

respectively. The amplitude of the correction signal is

adjustable. Small noise amplitudes in the correction sig-

nal are suppressed by an adjustable coring circuit. To

eliminate ‘wrong colors’, which are caused by over and

undershoots at the chroma transition, the sharpened

chroma signals are limited to a proper value automati-

cally.

Fig. 2–18: Digital Color Transient Improvement

Cr out

Cb out

Ampl.

Cr in

Cb in

a) Cr Cb input of DTI

b) Cr Cb input

)Correction signal

c) sharpened and limited Cr Cb

2.8.9. Inverse Matrix

A 6-multiplier matrix transcodes the Cr and Cb signals

to R–Y, B–Y, and G–Y. The multipliers are also used to

adjust color saturation in the range of 0 to 2. The coeffi-

cients are signed and have a resolution of 9 bits. There

are separate matrix coefficients for main and side pic-

tures. The matrix computes:

R–Y

+MR1*Cb)MR2*Cr

G–Y

+MG1*Cb)MG2*Cr

B–Y

+MB1*Cb)MB2*Cr

The initialization values for the matrix are computed

from the standard ITUR (CCIR) matrix:

* 0.345

1.773

1.402

* 0.713

For a contrast setting of CTM

+32, the matrix values are

scaled by a factor of 64, see also table 3–1.

2.8.10. RGB Processing

After adding the post-processed luma, the digital RGB

signals are limited to 10 bits. Three multipliers are used

to digitally adjust the white drive. Using the same multi-

pliers an average beam current limiter is implemented.

See also section 2.9.1. ‘CRT Measurement and Con-

trol’.

2.8.11. OSD Color Lookup Table

The VDP 31xxB has five input lines for an OSD signal.

This signal forms a 5-bit address for a color look-up table

(CLUT). The CLUT is a memory with 32 words where

each word holds a RGB value.

Bits 0 to 3 (bit 4

+0) form the addresses for the ROM part

of the OSD, which generates full RGB signals (bit 0 to 2)

and half-contrast RGB signals (bit 3).

Bit 4 addresses the RAM part of the OSD with 16 freely

programmable colors, addressable with bit 0 to 3. The

programming is done via the I2C-bus.

The amplitude of the CLUT output signals can be ad-

justed separately for R, G and B via the I2C-bus. The

switchover between video RGB and OSD RGB is done

via the Priority bus.

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