VDP3108 datasheet(13/61 Pages) MICRONAS

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ADVANCE INFORMATION

VDP 3108

MICRONAS INTERMETALL

2.4. Display Processor

In the display processor the conversion from digital

YCrCb to analog RGB is carried out. A block diagram is

shown in figure 2–18. In the luminance processing path

contrast and brightness adjustments and variety of fea-

tures such as black level expansion, dynamic peaking

and soft limiting are provided. In the chrominance path,

the CrCb signals are converted to 20.25 MHz sampling

rate and filtered by a color transient improvement circuit.

The YCrCb signals are converted by a programmable

matrix to RGB color space.

The signals inserted via the YCrCb bus are identified by

their respective priority. The display processor provides

separate control settings for two pictures, i.e. different

coefficients for a ‘main’ and a ‘side’ picture.

The digital RGB insertion circuit allows the insertion of

a 5 bit RGB signal. The color space for this signal is con-

trolled by a programmable color look up table (CLUT)

and contrast adjustment.

The RGB signals and the display clock are synchronized

to the horizontal flyback. For the display clock a gate

delay phase shifter is used. The RGB signals are syn-

chronized by a FIFO. In the analog back-end, three 10-

bit digital-to-analog converters provide the analog out-

put signals.

2.4.1. Contrast Adjustment

The 8 bit luminance input is multiplied by a factor of 0 ...

2 in 64 steps. A 2-bit noise shaping on the result is used

to increase the resolution of the luma signal. Contrast

adjustment is separate for main and side picture.

2.4.2. Black Level Expander

The black level expander enhances the contrast of the

picture. Therefore the luminance signal is modified with

an adjustable, nonlinear function. Dark areas of the pic-

ture are changed to black, while bright areas remain un-

changed. The advantage of this black level expander is

that the black expansion is performed only if there is a

large dynamic range in the video signal and when it will

be most noticeable to the viewer.

The black level expander works adaptively. Depending

on the measured amplitudes ‘Lmin’ and ‘Lmax’ of the low-

pass-filtered luminance and an adjustable coefficient

BTLT, a tilt point ‘Lt’ is being established by

Lt = Lmin + BTLT ( Lmax – Lmin).

Above this value there is no expansion, while all lumi-

nance values below this point are expanded according

to:

Lout = Lin + BAM (Lin – Lt)

A second threshold, Ltr, can be programmed, above

which there is no expansion. The characteristics of the

black level expander are shown in Fig. 2–14 and Fig.

2–15.

The tilt point Lt is a function of the dynamic range of the

video signal. Thus, the black level expansion is only per-

formed when the video signal has a large dynamic

range. Otherwise, the expansion to black is zero. This al-

lows the correction of the characteristics of the picture

tube.

Lin

Lout

Lmin

Lmax

Ltr

Fig. 2–14: Characteristics of the black

level expander

Ltr

BAM

BTHR

BTLT

Lmin

Lmax

Fig. 2–15: Black-level-expansion

a) luminance input

b) luminance output

2.4.3. Dynamic Peaking

Especially with composite input signals and notch filter

luminance separation, it is necessary to improve the lu-

minance frequency characteristics.

In DIGIT3000 the luma response is improved by ‘dynam-

ic’ peaking. The algorithm has been optimized regarding

step and frequency response. It adapts to the amplitude

of the high frequency part. Small amplitudes are en-

hanced while large amplitudes stay nearly unmodified.

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