tda8374bh NXP Semiconductors, tda8374bh Datasheet - Page 43

• Manufacturer Part Number: tda8374bh
• Description: Tda837x Family I?c-bus Controlled Economy Pal/ntsc And Ntsc Tv-processors
• Manufacturer: NXP Semiconductors

Philips Semiconductors
33. During switch-on the horizontal output starts with twice the frequency and with a duty cycle of 75% (V
34. The vertical blanking pulse in the RGB outputs has a width of 26 or 21 lines (50 or 60 Hz system). The width of the
35. The timing pulses for the vertical ramp generator are obtained from the horizontal oscillator via a divider circuit. This
36. Conditions: frequency is 60 Hz; normal mode; VS = 1F.
37. The output range percentages mentioned for E-W control parameters are based on the assumption that 400 A
38. The TDA8375 and TDA8377 have a zoom adjustment possibility for the vertical and horizontal deflection. For this
1997 Jul 01
I
and NTSC TV-processors
2
approximately 50 ms the frequency is changed to the normal value. Because of the high frequency the peak currents
in the horizontal output transistor are limited. Also during switch-off the frequency is switched to twice the value and
the RGB drive is set to maximum so that the EHT capacitor is discharged. This switching to maximum drive occurs
only when RBL = 0, for RBL = 1 the drive voltage remains minimum during switch-off. After approximately 100 ms
the RGB drive is set to minimum and 50 ms later the horizontal drive is switched off.
The horizontal output is gated with the flyback pulse so that the horizontal output transistor cannot be switched on
during the flyback time.
vertical sync pulse in the sandcastle pulse has a width of 14 lines. This to prevent a phase distortion on top of the
picture due to timing modulation of the incoming flyback pulse.
divider circuit has 3 modes of operation. A brief explanation is given below. For the TDA8373 and TDA8377 only the
60 Hz figures are valid.
a) Search mode ‘large window’:
b) Standard mode ‘narrow window’:
c) Standard TV-norm (divider ratio 525 (60 Hz) or 625 (50 Hz):
The vertical divider needs some waiting time during channel-switching of the tuner. When a fast reaction of the
divider is required during channel-switching the system can be forced to the search window by means of the NCIN bit
in subaddress 08.
variation in E-W output current is equivalent to 20% variation in picture width. Because of the horizontal and vertical
zoom feature in the TDA8375 and TDA8377 (see also note 38) the E-W width control range is increased compared
with previous ICs such as the TDA8366. The increased E-W width control is also available in the TDA8375A and
TDA8377A although these devices do not have the vertical zoom feature.
reason an extra DAC has been added in the vertical amplitude control which controls the vertical scan amplitude
between 0.75 and 1.38 of the nominal scan. At an amplitude of 1.08 of the nominal scan the output current is limited
and the blanking of the RGB outputs is activated (see Fig.28). In addition to the variation of the vertical amplitude the
vertical slope control range is also increased. This gives the possibility to vary the position of the bottom part of the
picture independent from the upper part. The nominal scan height must be adjusted at a position of 19H of the vertical
‘zoom’ DAC
C-bus controlled economy PAL/NTSC
This mode is switched on when the circuit is not synchronized or when a non-standard signal (number of lines
per frame in the 50 Hz mode is between 311 and 314 and in the 60 Hz mode between 261 and 264) is received.
In the search mode the divider can be triggered between line 244 and line 361 (approximately 45 to 64.5 Hz).
This mode is switched on when more than 15 succeeding vertical sync pulses are detected in the narrow window.
When the circuit is in the standard mode and a vertical sync pulse is missing the retrace of the vertical ramp
generator is started at the end of the window. Consequently, the disturbance of the picture is very small.
The circuit will switch back to the search window when, for 6 successive vertical periods, no sync pulses are found
within the window.
When the system is switched to the narrow window it is checked whether the incoming vertical sync pulses are
in accordance with the TV-norm. When 15 standard TV-norm pulses are counted the divider system is switched
to the standard divider ratio mode. In this mode the divider is always reset at the standard value even if the vertical
sync pulse is missing.
When 3 vertical sync pulses are missed the system switches back to the narrow window and when also in this
window no sync pulses are found (condition 3 missing pulses) the system switches over to the search window.
43
TDA837x family
Preliminary specification
o
= HIGH). After