2.1 Video and Sound IF System & Switch IC STV8223:
STV 8223 is a picture and sound IF processor for negative application. The architecture of the video and
sound demodulator, which are both based on PLL structure, allows a very good linearity of the Intermediate
Frequency Response and an application with very few external components and adjustments.
The volume on the audio signal is controlled through a DC level (pin #13) which is provided from STV 2112/
2
2116/2118 where all the IC decoding is realized.
STV 8223 also provides the audio and video switches for scart - AV applications. The IF inputs at pins #19
and #20 are driven by Tuner via Saw filter (Z101). The baseband signal(CVBS) produced from these IF
inputs appears at pin #3. This signal is used to produce video signal and intercarrier sound signal.This
internal video signal, which is produced by using the Z107 trap filter ,is fed to pin #10 of this IC for internal-
external (coming from scart) video switching and to the base of the buffer transistor Q102 for the video output
of the scart connector. The intercarrier signal used to reproduce the sound, passes through the band pass
filter Z103 with center frequency 5.5MHz for B/G standard or Z104 for I (6.0MHz) or Z105 for D/K (6.5MHz)
in according to selected system by intercarrier signal switching circuitry (D106, D107, D108, D109) and
resultant signal is applied to the pin #8 of the IC which is the input of limiter and SIF PLL stage. The switch
control signal is supplied by microcontroller. The limiter and SIF PLL output pin #15 which is connected to the
deemphasis capacitor drives audio out of the scart connector and AV jack. The external inputs of IC, which
are pin #12 for video and pin #16 for audio, are connected to the related scart connector inputs or AV RCA
jack inputs. The internal-external selection for monitoring is made by control voltage at pin #8 produced by
microcontroller and switching between 4/3 and 16/9 picture modes is also carried out by the voltage level at
pin #8 of the scart . The selected video at pin #11 drives video processing stage. On the other hand, the
selected audio is processed in volume control stage in according with DC control voltage at pin #13 and then,
it is sent from pin #14 to sound output stage.
The IF block produces control signals, which are AGC for tuner at pin #23 in according to voltage of pin #24
controlled by microcontroller pin #48.
2.2 Multi-Standard Video IF, Sound IF and Switch IC (STV 8224)
and AM Sound IF IC (STV 8225) :
STV 8224 is a picture and sound IF processor for negative and positive applications. The architecture of the
video and sound demodulator, which are both based on PLL structure, allows a very good linearity of the
Intermediate Frequency Response and an application with very few external components and adjustments.
The volume on the audio signal is controlled through a DC level (pin #13) which is provided from STV 2112/
2
2116/2118 where all the IC decoding is realized.
STV 8224 also provides the audio and video switches with STV 8225 for one scart applications.
The IF inputs at pins #19 and #20 are driven by Tuner via SAW filter (Z101) which is K6256 for B/G - L/L?
applications. This saw filter is switchable according to a control signal produced by microcontroller(pin #13).
The baseband signal(CVBS) at pin #3 is produced from these IF inputs and selection between external and
internal is carried out according to the switching control signal at pin #4. This control signal comes from
STV2118.
The baseband signal is used to produce the video signal and on the other hand to produce intercarrier sound
signal. This internal video signal is fed to pin #10 of this IC for internal-external (from scart) video switching
and to the base of the buffer transistor Q102 for the video output of the scart connector. For the internal and
external video switching, external video enters from pin #12, and then, selected video is sent from pin #11 to
video processing part.
The intercarrier signal ,used for reproducing the sound, passes through the band pass filter Z103 with center
frequency 5.5MHz for B/G standard and resultant signal is applied to the pin #8 of the IC STV 8224 which is
the input of limiter and SIF PLL stage. The limiter and SIF PLL output pin #15 which is connected to the
deemphasis capacitor drives pin #5 of the IC STV 8225 as FM Sound Input in order to be able to select the
appropriate (FM or AM) audio signal for producing audio out of the scart connector. The selected signal at pin
#9 of STV8225 drives external audio output connections. On the other hand, the audio switch in STV 8224 is
used to select the internal FM signal or the output of STV 8225 (pin #7), which selects the internal AM signal
or External audio signal (at pin #11) coming from scart socket. The selected audio is processed in volume
control stage in according with DC control voltage at pin #13 and then, it is sent from pin #14 to sound output
stage. The IF signal is filtered at Z102 saw filter which is switchable according to the control signals produced
by microcontroller for L or L? mode. Output of SAW is connected to pin #1 and #14 of SIF IC STV 8225(IC
102) for AM demodulation of sound. The audio switches in STV 8225 selects the signals according to DC
voltage at pin #10 of STV8225.
The IF block produces control signals, which are AGC for tuner at pin #23 in according to voltage of pin #24
controlled by microcontroller and AFC for microcontroller at pin #48.
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