TDA4681 Datasheet, PDF (18/28 Pages) NXP Semiconductors – Video processor with automatic cut-off and white level control

Philips Semiconductors
Video processor with automatic cut-off
and white level control
Product specification
TDA4681
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
PARAMETER
(B − Y)* demodulator axis
(R − Y)* demodulator axis
(R − Y)* amplification factor
(B − Y)* amplification factor
NTSC
PAL
0°
0°
95°
90°
1.59
1.14
2.03
2.03
Table 6 PAL/SECAM and NTSC matrix; notes 1 and 2
MATRIX
PAL/SECAM
NTSC
NMEN
0
1
Notes
1. PAL/SECAM signals are matrixed by the equation: V_{G − Y} = −0.51V_{R − Y} − 0.19V_{B − Y}
NTSC signals are matrixed by the equations (hue phase shift of −5 degrees):
V_{R − Y*} = 1.39V_{R − Y} − 0.07V_{B − Y}; V_{G − Y*} = −0.46V_{R − Y} − 0.15V_{B − Y}; V_{B − Y*} = V_{B − Y}
In the matrix equations: V_{R − Y} and V_{B − Y} are conventional PAL demodulation axes and amplitudes at the output of
the NTSC demodulator. V_{G − Y*}, V_{R − Y*} and V_{B − Y*} are the NTSC modified colour difference signals; this is equivalent
to the demodulator axes and amplification factors shown in Table 5. V_{G − Y*} = −0.33V_{R − Y*} − 0.17V_{B − 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.
1997 Mar 04
18