TDA935x Philips, TDA935x Datasheet - Page 97

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

Philips Semiconductors
38. The slicing level is independent of sync pulse amplitude. The given percentage is the distance between the slicing
39. To obtain a good performance for both weak signal and VCR playback the time constant of the first control loop is
40. The ICs have 2 protection inputs. The protection on the second phase detector pin is intended to be used as ‘flash’
41. The control range indicates the maximum phase difference at the top and the bottom of the screen. Compared with
42. During switch-on the horizontal drive starts-up in a soft-start mode. The horizontal drive starts with a very short T
2001 Jan 18
TV signal processor-Teletext decoder with
embedded -Controller
level and the black level (back porch). When the amplitude of the sync pulse exceeds the value of 350 mV the sync
separator will slice the sync pulse at a level of 175 mV above top sync. The maximum sync pulse amplitude is 4 V
The vertical slicing level is dependent on the S/N ratio of the incoming video signal. For a S/N
level is 35%, for a S/N
level can be forced to 60%.
switched depending on the input signal condition and the condition of the POC, FOA, FOB and VID bits in
subaddress 24H. The circuit contains a noise detector and the time constant is switched to ‘slow’ when too much
noise is present in the signal. In the ‘fast’ mode during the vertical retrace time the phase detector current is increased
50% so that phase errors due to head-switching of the VCR are corrected as soon as possible. Switching of the time
constant can be automatically or can be set by means of the control bits.
The circuit contains a video identification circuit which is independent of the first loop. This identification circuit can
be used to close or open the first control loop when a video signal is present or not present on the input. This enables
a stable On Screen Display (OSD) when just noise is present at the input.
To prevent that the horizontal synchronisation is disturbed by anti copy signals like Macrovision the phase detector
is gated during the vertical retrace period so that pulses during scan have no effect on the output voltage. The width
of the gate pulse is about 22 s. During weak signal conditions (noise detector active) the gating is active during the
complete scan period and the width of the gate pulse is reduced to 5.7 s so that the effect of noise is reduced to a
minimum.
The output current of the phase detector in the various conditions are shown in Table 133.
protection. When this protection is activated the horizontal drive is switched-off immediately and then switched-on
again via the slow start procedure.
The protection on the EHT input is intended for overvoltage (X-ray) protection. When this protection is activated the
horizontal drive is directly switched-off (via the slow stop procedure).
The EHT protection input can also be used to switch-off the TV receiver in a correct way when it is switched off via
the mains power switch or when the power supply is interrupted by pulling the mains plug. This can be realised by
means of a detection circuit which monitors the main supply voltage of the receiver. When this voltage suddenly
decreases the EHT protection input must be pulled HIGH and then the horizontal drive is switched off via the slow
stop procedure. Whether the EHT capacitor is discharged in the overscan or not during the switch-off period depends
on the setting of the OSO bit (subaddress 25H, D4). See also note 59.
the phase position at the centre of the screen the maximum phase difference at the top and the bottom of the screen
is 0.5 s for both the parallelogram and the bow correction.
time of the horizontal output transistor, the ‘off time’ of the transistor is identical to the ‘off time’ in normal operation.
The starting frequency during switch-on is therefore about 2 times higher than the normal value. The ‘on time’ is
slowly increased to the nominal value in a time of about 1175 ms (see Fig.43). The rather slow rise of the T
between 75% and 100% of T
Dynamic Astigmatic Focus (DAF) guns. When the nominal frequency is reached the PLL is closed in such a way that
only very small phase corrections are necessary. This ensures a safe operation of the output stage.
During switch-off the soft-stop function is active. This is realised by decreasing the T
complimentary to the start-up behaviour. The switch-off time is about 43 ms (see Fig.43). When the ‘switch off
command’ is received the soft-stop procedure is started after a delay of about 2 ms. During the switch-off time the
EHT capacitor of the picture tube is discharged with a fixed beam current which is forced by the black current loop
(see also note 59). The discharge time is about 38 ms.
The horizontal output is gated with the flyback pulse so that the horizontal output transistor cannot be switched-on
during the flyback time.
24 dB the slicing level is 60%. With the bit FSL (Forced Slicing Level) the vertical slicing
ON
is introduced to obtain a sufficiently slow rise of the EHT for picture tubes with
97
TDA935X/6X/8X PS/N2 series
ON
Tentative Device Specification
of the output transistor
24 dB the slicing
ON
ON
p-p
.