TDA935x Philips, TDA935x Datasheet - Page 99

• Manufacturer Part Number: TDA935x
• Description: TV Signal Processor-Teletext Decoder with Embedded u-Controller
• Manufacturer: Philips

Philips Semiconductors
52. Because of the 2-point black current stabilization circuit both the black level and the amplitude of the RGB output
53. The alignment system for the V
54. When the reproduction of 4 : 3 pictures on a 16 : 9 picture tube is realised by means of a reduction of the horizontal
55. This parameter is valid only when the CCC loop is active.
56. Signal-to-noise ratio (S/N) is specified as peak-to-peak signal with respect to RMS noise (bandwidth 5 MHz).
57. This is a current input. The timing of the measuring pulses and the vertical blanking for the 50/60 Hz standard are
58. The input of the vertical guard function can be connected to the black current measuring input (BLKIN) or to the beam
2001 Jan 18
TV signal processor-Teletext decoder with
embedded -Controller
signals depend on the drive characteristic of the picture tube. The system checks whether the returning measuring
currents meet the requirement and adapts the output level and gain of the circuit when necessary. Therefore the
typical value of the black level and amplitude at the output are just given as an indication for the design of the RGB
output stage.
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.
given in Fig.44
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.
current limiting input (BCLIN). The switching between these modes is realised by means of the IVG bit in subaddress
2BH. When the black current input is chosen it should be noted that for a reliable operation of the protection system
and the black current stabilization system the end of the protection pulse during normal operation should not overlap
the measuring pulses (see also Fig.44). Therefore this pulse must end before line 14.
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
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TDA935X/6X/8X PS/N2 series
g2
Tentative Device Specification
of the picture tube can be