MP4680 datasheet(18/28 Pages) PHILIPS

18 / 28 page

1996 Oct 25

Philips Semiconductors

Product speciﬁcation

Video processor with automatic cut-off and

white level control

TDA4680

9. The vertical blanking interval is defined by a vertical pulse which contains 4 (8) or more horizontal pulses; it begins

with the start of the vertical pulse and ends with the end of the white measuring line. If the vertical pulse is longer

than the selected vertical blanking window the blanking period ends with the end of the complete line after the end

of the vertical pulse. The counter cycle time is 31 (63) horizontal pulses. If the vertical pulse contains more than

29 (57) horizontal pulses, the black level storage capacitors will be discharged while all signals are blanked.

During leakage current measurement, the RGB channels are blanked to ultra-black level. During cut-off

measurement one channel is set to the measurement pulse level, the other channels are blanked to ultra-black.

Since the brightness adjust shifts the colour signal relative to the black level, the brightness adjust is disabled during

the vertical blanking interval (see Figs 7 and 8).

10. During picture cathode warming up (first switch-on delay) the RGB outputs (pins 24, 22 and 20) are blanked to the

ultra-black level during line scan. During the vertical blanking interval a white-level monitor pulse is fed out on the

RGB outputs and the cathode currents are measured. When the voltage threshold on pin 19 is greater than 5.0 V,

the monitor pulse is switched off and cut-off and white level control are activated (second switch-on delay). As soon

as cut-off control stabilizes, RGB output blanking is removed.

11. Range of cut-off measurement level at the RGB outputs is 1 to 5 V. The recommended value is 3 V.

12. The hue control output at pin 26 is an emitter follower with current source.

Table 5

Demodulator axes and ampliﬁcation factors

Table 6

PAL/SECAM and NTSC matrix; notes 1 and 2

Notes

1. PAL/SECAM signals are matrixed by the equation: VG − Y = −0.51VR − Y − 0.19VB − Y

NTSC signals are matrixed by the equations (hue phase shift of

−5 degrees):

VR − Y* = 1.57VR − Y − 0.41VB − Y; VG − Y* = −0.43VR − Y − 0.11VB − Y; VB − Y* =VB − Y

In the matrix equations: VR − Y and VB − Y are conventional PAL demodulation axes and amplitudes at the output of

the NTSC demodulator. VG − Y*, VR − Y* and VB − Y* are the NTSC-modified colour difference signals; this is equivalent

to the demodulator axes and amplification factors shown in Table 5. VG − Y* = −0.27VR − Y* − 0.22VB − Y*.

2. The vertical blanking interval is selected via the I2C-bus (see Table 2 and Fig.8). Vertical blanking is determined by

the vertical component of the sandcastle pulse; this vertical component has priority when it is longer than the vertical

blanking interval of the transmission standard.

PARAMETER

NTSC

PAL

− Y)* demodulator axis

115

− Y)* ampliﬁcation factor

1.97

1.14

− Y)* ampliﬁcation factor

2.03

MATRIX

NMEN

PAL/SECAM

NTSC

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