3.1 Bus-controlled Multi-Standard TV Processor IC, STV 2118 :
The STV 2118 (IC 401) is a fully bus controlled IC for TV Luma, Chroma and Deflection processing. In order to
make the alignments by microcontroller via I2C, the required data are transferred from microcontroller into the
related registers of STV 2118. The main input for this IC are as follws :
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?IC Inputs from microcontrolle
? Y/CVBS Input from IF Part, external CVBS coming from scart or front AV RCA jack, external RGB and Fast
Blank signals coming from Scart, R input is also used for Chroma input in SVHS Mode
? OSD and TELETEXT RGB and Fast Blank signals coming form both microcontroller and teletext processor IC
? BCI (Black Current Information) coming from CRT Baseboard
? BCL (Beam Current Limiting) information from Horizontal Output Stage
? Line Flyback Sample coming from Horizontal Output Stage
? Delayed R-Y and B-Y signals coming from Delay Line IC STV 2180
Detailed Features and the internal block diagram of the IC STV 2118 are given in following subsections:
3.1.1 Deflection Circuit :
The deflection part includes a fully integrated sync-separator locked to a 500 kHz VCO with external resonator
(X401), two phase locked loops for horizontal deflection, vertical count down with 50 Hz and 60 Hz operation for field
frequency.
Vertical output pulse is 10.5 lines long at pin # 35, furthermore horizontal output pulse is 28 msec on open
collector pin # 36.
The horizontal output is at high level when Vcc increases from 0V to 6.8V. On shutting down, the horizontal pulse
disabled when Vcc is below 6.2V.
When vertical pulses are disappeared, horizontal output is disabled by microcontroller for keeping CRT phosphor.
Line position adjustment is controlled by bus using related service mode.
Bus controlled output voltage at pin # 34 is used to adjust vertical amplitude at vertical output stage via R705,
R706 and R707.
Bus controlled vertical position information is produced from high level of the vertical pulse pin # 35 and this
signal is used to adjust vertical positioning at vertical output stage via R701, R703, R704, C701, D701 and Q701.
The sandcastle signal at pin # 37 is used to control the external baseband chroma delay line
(STV 2180 -IC 402- pin # 6).
3.1.2 Filters :
All filters (integrated trap filter, integrated chroma bandpass, integrated bell filter for SECAM, integrated delay line)
are tuned with a reference PLL.
The PLL consists of a lowpass filter, a phase comparator, a loop filter (an external capacitor C423 on pin # 8).
The reference signal is the continuous carrier wave from the VCO (4.43 MHz or 3.58 MHz). The PLL will adjust the
center frequency of the lowpass so that it will be equal to the reference signal. The tuning voltage of the PLL
(memorized on pin # 8) will adjust all other filters.
The cloche filter is fine-tuned with a second PLL operating during frame retrace. Tuning voltage is memorized on an
external capacitor C424 at pin # 9.
3.1.3 Video Circuit :
Video part includes two RGB inputs, automatic cut-off control, DC cut-off adjustment, RGB gain adjustments,
beam current limiting. Furthermore, user video settings (contrast, saturation, brightness and sharpness controls)
are performed by this block. RGB output pins are as follows: R output is pin # 29, G output is pin # 28 and B output
is pin # 27.
The beam current information is fed to pin # 31 via R411 and D403. This control voltage will act on contrast first,
then the brightness will be decreased when contrast attenuation reaches -5dB.
Automatic cut-off function is realized according to the BCI information at pin # 30. Sequential cut-off current
measurements are made during three lines after frame blanking signal.
3.1.4 Chroma Circuit :
The chroma part includes PAL, SECAM, NTSC demodulator. An external base band delay line (STV 2180 IC402)
is used in this concept. R-Y and B-Y outputs of STV 2118 (pin # 40 and pin # 41) are sent to STV 2180 to get 64msec
delayed signals.
The PAL, SECAM or NTSC standard selection is made by automatic standard identification.
Three X?tals for PAL M (X404), PAL N (X405) and NTSC M (X403) and their switching circuitry (Q401, Q402, Q403,
Q404, D401, D402) are used in PAL M/N and NTSC M models only.
SVHS selection is made by microcontroller via bus control.
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