參數(shù)資料
型號： TDA935X
廠商： NXP Semiconductors N.V.
英文描述： TV signal processor-Teletext decoder with embedded m-Controller
中文描述： 電視信號處理器與嵌入式米圖文電視解碼器控制器
文件頁數(shù)： 124/140頁
文件大?。?/td> 570K
代理商： TDA935X
1999 Sep 28
124
Philips Semiconductors
Preliminary Device Specification
TV signal processor-Teletext decoder with
embedded
μ
-Controller
TDA935X/6X/8X series
41. The timing pulses for the vertical ramp generator are obtained from the horizontal oscillator via a divider circuit.
During TV reception this divider circuit has 3 modes of operation:
a) Search mode ‘large window’.
This mode is switched on when the circuit is not synchronized or when a non-standard signal (number of lines
per frame outside the range between 311 and 314(50 Hz mode) or between 261 and 264 (60 Hz mode) is
received). In the search mode the divider can be triggered between line 244 and line 361 (approximately
45 to 64.5 Hz).
b) Standard mode ‘narrow window’.
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.
c) Standard TV-norm (divider ratio 525 (60 Hz) or 625 (50 Hz).
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.
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 25H.
When RGB signals are inserted the maximum vertical frequency is increased to 72 Hz. This has the consequence
that the circuit can also be synchronised by signals with a higher vertical frequency like VGA.
42. Conditions: frequency is 50 Hz; normal mode; VS = 1F.
43. The output range percentages mentioned for E-W control parameters are based on the assumption that 400
μ
A
variation in E-W output current is equivalent to 20% variation in picture width.
44. The ICs have a zoom adjustment possibility for the horizontal and vertical deflection. For this 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 1.06 of the nominal scan the output current is limited and the blanking of the
RGB outputs is activated. This is illustrated in Fig.53.
The nominal scan height must be adjusted at a position of 19 HEX of the vertical ‘zoom’ DAC.
45. At a chrominance input voltage of 660 mV (p-p) (colour bar with 75% saturation i.e. burst signal amplitude
300 mV (p-p)) the dynamic range of the ACC is +6 and
20 dB.
46. The ACL function can be activated by via the ACL bit in the subaddress 20H. The ACL circuit reduces the gain of the
chroma amplifier for input signals with a chroma-to-burst ratio which exceeds a value of 3.0.
47. This parameter indicates the bandwidth of the complete chrominance circuit including the chrominance bandpass
filter. The bandwidth of the low-pass filter of the demodulator is approximately 1 MHz.
48. The subcarrier output is combined with a 3-level switch output which can be used to switch external circuits like
sound traps etc. This output is controlled by the CMB1 and CMB0 bits in control byte 22H. The subcarrier signal is
available when CMB1/0 are set to 0/1. When CMB1/0 are set to 00 in versions for 90
°
picture tubes (no EW output)
this pin is switched to external sound IF input.
49. Because of the 2-point black current stabilization circuit both the black level and the amplitude of the RGB output
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.
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