TDA9550 PHILIPS [NXP Semiconductors], TDA9550 Datasheet - Page 104

• Manufacturer Part Number: TDA9550
• Description: TV signal processor-Teletext decoder with embedded m-Controller
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
57. The alignment system for the V
58. When the reproduction of 4 : 3 pictures on a 16 : 9 picture tube is realised by means of a reduction of the horizontal
59. Signal-to-noise ratio (S/N) is specified as peak-to-peak signal with respect to RMS noise (bandwidth 5 MHz).
60. This is a current input. The timing of the measuring pulses and the vertical blanking for the 50/60 Hz standard are
61. The vertical guard function has been combined with the black current measuring input. For a reliable operation of the
62. During switch-off the magnitude of the discharge current of the picture tube is controlled by the black current loop.
2000 Jun 22
TV signal processor-Teletext decoder with
embedded -Controller
The 2-point black level system adapts the drive voltage for each cathode in such a way that the 2 measuring currents
have the right value. This has the consequence that a change in the gain of the output stage will be compensated
by a gain change of the RGB control circuit. Because different picture tubes may require different drive voltage
amplitudes the ratio between the output signal amplitude and the inserted measuring pulses can be adapted via the
I
Because of the dependence of the output signal amplitude on the application the soft clipping limiting has been
related to the input signal amplitude.
condition a certain black level is inserted at the RGB outputs during a few lines. The value of this level can be
adjusted by means of the brightness control DAC. An automatic adjustment of the V
realised by using the WBC and HBC bits in output byte 01. For a black level feedback current between 12 and 20 A
the WBC = 1, for a higher or lower current WBC = 0. Whether the current is too high or too low can be found from
the HBC bit. The indication of these bits can be made visible on the screen via OSD so that this alignment procedure
can also be used for service purposes.
scan amplitude the edges of the picture may slightly be disturbed. This effect can be prevented by adding an
additional blanking to the RGB signals. The blanking pulse is derived form the horizontal oscillator and is directly
related to the incoming video signal (independent of the flyback pulse). This blanking is activated with the HBL bit.
The width of the blanking can be set by means of the bits WBF3-WBF0 (start of blanking) and WBR3-WBR0 (end of
blanking) in subaddress 03H (see Fig.48).
given in Fig.46
The start-up procedure is as follows.
When the TV receiver is switched-on the RGB outputs are blanked and the black-current loop will try to adjust the
picture tube to the right bias levels. The RGB drive signals are switched-on as soon as the black current loop is
stabilised. This results in the shortest switch-on time.
When this switch-on system results in a visible disturbance of the picture it is possible to add a further switch-on delay
via a software routine. In that case the RGB outputs must be blanked by means of the RBL bit. As soon as the black
current loop is stabilised the BCF-bit is set to 0 (output byte 01). This information can then be used to switch-on the
RGB outputs with some additional delay.
protection system and to avoid that the black current stabilization system is disturbed the end of the protection pulse
during normal operation should not overlap the measuring pulses (see also Fig.46). Therefore this pulse must end
before line 14.
Dependent on the setting of the OSO bit the vertical scan can be stopped in an overscan position during that time so
that the discharge is not visible on the screen. The switch-off procedure is as follows:
a) When the switch-off command is received the RGB outputs are blanked for a time of about 2 ms.
b) If OSO = 1 the vertical scan is placed in an overscan position
c) If OSO = 0 the vertical deflection will keep running during the switch-off time
d) The soft-stop procedure is started with a reduction of the T
e) The fixed beam current is forced via the black current loop
The soft-stop time has a value of 43 ms, the fixed beam current is flowing during a time of 38 ms.
2
C-bus. This is indicated in the parameter ‘Adjustment range of the cathode drive level’.
g2
voltage of the picture tube can be activated by means of the AVG bit. In that
104
ON
of the output stage from nominal to zero
TDA955X/6X/8X PS/N1 series
g2
Tentative Device Specification
of the picture tube can be