SAA4977H/V1 Просмотр технического описания (PDF) - Philips Electronics

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SAA4977H/V1

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Philips Electronics 

Philips Semiconductors

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Preliminary specification

SAA4977H

7.2.5 HORIZONTAL COMPRESSION

For displaying 4 : 3 sources on 16 : 9 screens a horizontal

signal compression can be done by data interpolation.

Therefore two horizontal compression factors of either

4⁄3 or 7⁄6 are possible. Via the I2C-bus the compression can

be switched on or off and the compression mode 16 : 9 or

14 : 9 can be selected. When the compression mode is

active, a reduced number of the interpolated data is stored

in the field memory. To achieve sufficiently high accuracy

in interpolation Variable Phase Delay filters are used

(VPD10 for luminance, a multiplexed VPD06 for UV).

7.3 Digital processing at 2fH level

7.3.1 4 : 1 : 1 TO 4 : 2 : 2 UP-CONVERSION

An up-converter to 4 : 2 : 2 is applied with a linear

interpolation filter for creation of the extra samples. These

are combined with the original samples from the 4 : 1 : 1

stream.

7.3.2 DCTI

The Digital Colour Transient Improvement (DCTI) is

intended for U and V signals originating from a 4 : 1 : 1

source. Horizontal transients are detected and enhanced

without overshoots by differentiating, make absolute and

again differentiating the U and V signals separately.

This results in a 4 : 4 : 4 U and V bandwidth. To prevent

third harmonic distortion, typical for this processing, a so

called over the hill protection prevents peak signals

becoming distorted. Via the I2C-bus it is possible to

control: gain width (see Fig.4), threshold (i.e. immunity

against noise), selection of simple or improved first

differentiating filter (see Fig.3), limit for pixel shift range

(see Fig.5), common or separate processing of U and V

signals, hill protection mode (i.e. no discolourations in

narrow colour gaps), low-pass filtering for U and V signals

(see Fig.6) and a so called super hill mode, which avoids

discolourations in transients within a colour component.

7.3.3 Y-PEAKING

A linear peaking is applied, which amplifies the luminance

signal in the middle and the upper ranges of the

bandwidth.

The filtering is an addition of:

• The original signal

• The original signal high-passed with maximum gain at

frequency = 1⁄2fs (8 MHz)

• The original signal band-passed with centre

frequency = 1⁄4fs (4 MHz)

• The original signal band-passed with centre frequency

of 2.38 MHz.

The band-passed and high-passed signals are weighted

with factors 0, 1⁄16, 2⁄16, 3⁄16, 4⁄16, 5⁄16, 6⁄16, and 8⁄16, resulting

in a maximum gain difference of 2 dB at the centre

frequencies.

Coring is added to obtain no gain for low amplitudes in the

high-pass and band-pass filtered signal, which is

considered to be noise. Coring levels can be programmed

as 0 (off), ±8, ±16, ±24 to ±120 LSB w.r.t. the (signed)

11-bit filtered signal.

In addition the peaking gain can be reduced depending on

the signal amplitude, programming range 0 (no

attenuation), 1⁄4, 2⁄4, and 4⁄4. It is also possible to make

larger undershoots than overshoots, programming range 0

(no attenuation of undershoots), 1⁄4, 2⁄4, and 4⁄4.

7.3.4 Y-DELAY

The Y samples can be shifted onto 8 positions w.r.t. the

UV samples. This shift is meant to account for a possible

difference in delay previous to the SAA4977H. The zero

delay setting is suitable for the nominal case of aligned

input data. The other settings provide one to seven

samples less delay in Y.

7.3.5 SIDEPANELS AND BLANKING

Sidepanels are generated by switching Y and the 4 MSBs

of U and V to certain programmable values. The start and

stop values for the sidepanels w.r.t. the rising edge of the

HRD signal are programmable in a resolution of 4 LLD

clock cycles. In addition, a fine shift of 0 to 3 LLD clock

cycles of both values can be achieved.

Blanking is done by switching Y to value 64 at 10-bit word

and UV to value 0 (in 2’s complement). Blanking is

controlled by a composite signal HVBDA, consisting of a

horizontal part HBDA and a vertical part VBDA. Set and

reset value of the horizontal control signal HBDA are

programmable w.r.t. the rising edge of the HRD signal, set

and reset value of the vertical control signal VBDA are

programmable w.r.t. the rising edge of the VA signal.

The range of the Y output signal can be selected between

9 and 10 bits. In the case of 9 bits for the nominal signal

there is room left for undershoot and overshoot (adding up

to a total of 10 bits). In the case of selecting all 10 bits of

the luminance DAC for the nominal signal any under or

overshoot will be clipped (see Fig.11).

1998 Jul 23

9

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