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Schaltungsbeschreibung / Circuit Description
The output of each peak detector is a voltage stored in its NRS time
constant. This is a DC level which will vary with the amplitude of the
audio channel signal and is used to control the frequency response of
its NRS filter via a variable transconductance amplifier.
Switch S3 is used to select the NRS system.
Audio Processing Block Diagram
I C 1100 STV 00 56A
S3
S2
N RS
S1
6dB
-
6dB
28,27
25,24
3,53
2,54
51,52
1,55
Peak
D etector
B and-Pass
Fi l ter
4.2 Passive Deemphasis
S4 is used to select the type of passive deemphasis that is applied to
each audio channel. The options are set by external networks and are
J17, and 75µS. 50µS is obtained by adding an internal resistor in
parallel with the 75µS network.
For PANDA operation NRS and 75µS are used together.
5. Video Noise Filter
The baseband signal from the tuner is passed through a 10MHz low-
pass filter consisting of L2116, CC2113, CC2010 and CC2009, to remove
unwanted noise before it is taken to the Video Processor IC2100-(20)
for further processing.
6. Video Processing
6.1 Video Gain Control in IC2100
Baseband Video from the Tuner section is AC-coupled into a controlled
amplifier whose gain can be set to give the desired Video amplitude.
6.2 Video Inverter
The polarity of the video signal can be set by the invert switch so that,
for instance, C-band reception can be achieved.
After the invert selector switch this signal forms the BASEBAND input
to the Video Matrix and PAL Deemphasis.
6.3 PAL Deemphasis
The baseband signal is applied to the non-inverting input of an amplifier
which has a PAL Deemphasis network in its feedback loop.
After the deemphasis the PAL signal is band limited by the 5MHz low-
pass filter. In the following, the signal is AC-coupled into the clamp to
remove the 25Hz energy dispersal waveform. The resulting signal is
the NORMAL video input to the Video Matrix.
6.4 Video Matrix IC2100
This is a cross wire matrix of switches which can select any one of the
Video sources and make it available to each of the three outputs. In
addition to the SAT-video signals described above video is also fed to
the matrix from the VCR and DEC sockets, each signal being clamped
to the same level to avoid switching disturbances. All Video Matrix,
Invert and Video Gain are controlled via I
the matrix is sent to the TV, VCR and DEC socket.
Megalogic control is possible via contact 10 of the SCART sockets
(passive connection).
6.4.1 TV Socket
By a "High" level switching voltage U
switching voltage is fed through CT1254, CT1250 to the TV Scart
socket, contact 8, and consequently the TV receiver is switched to the
AV mode.
2 - 6
{
SD A
I
2
C B us
SCL
30
31
S4
S6
Passi v e
A udi o
D e-em phasi s
V o l
S5
6dB
-
6dB
33,34
48,40
14,12
22,21
6,10
C-bus. The output signal from
2
CIC1401-(39), the 12V
AV OUT 3
The OSD signal is taken from the output IC1331-(16) via CT1260 to the
TV socket (contact 19).
IC1100 STV0056A
Baseband Video
Video Gain
From Tuner
20
13
Clamp
From Decoder
5
Clamp
From
11
Clamp
VCR SCART
4
Clamp
Video Processing Block Diagram
6.4.2 VCR Socket
The audio and video signals to be recorded are provided on contact 1/
6 and 19 respectively of the VCR socket.
On VCR playback the IC2100 applies the audio/video signal to the TV
socket via the switching voltage from the VCR socket - contact 8, U
CIC1401-(22).
6.4.3 Decoder Socket
On Decoder operation, the switching voltage from the DEC socket -
contact 8, U
CIC1401-(21) - feeds the descrambled audio/video
AV IN 1
signal to the TV and VCR socket.
On RGB operation, the RGB switching voltage from the DEC socket -
contact 16 connects the RGB signal via CT1276 to the TV socket. The
TV receiver changes to RGB mode.
If a switching voltage is simultaneously applied to contact 8 of the VCR
socket, the switching voltage U
RGB TV
the RGB switching voltage at the TV socket is switched off by CT1270.
VCR priority operation: the VCR-signal is only fed through the Video Matrix
IC2100 to contact 19 of the TV socket.
6.4.4 Signal Switch-over to Modulator
Dependent on the selected operating mode the video signal is fed to
the modulator, contact 3, via the transistor CT1406.
The audio signals AR
and AL
TVOUT
transistors CT1405 or CT1400 and the operational amplifier CIC1330
to modulator contact 1 or to socket 1 and socket 2.
7. OSD Insertion and Synchronisation
The video signal "V
" via CT1365 is used as the feed for the On
VID OUT
Screen Display (OSD) insertion circuit IC1331 which adds menus and
status information to the video signal to be displayed on the TV. The
sync tips of the video signal "V
VID OUT
level by CT1350.
The presence of a standard sync is signalled by a "High" level at
IC1331-(29). From a level of >4V, CIC1401-(19) recognizes via the
"U
" lead that a valid sync signal is present and indicates the
EXO SYNC.
display field.
In the absence of a valid sync signal, the OSD processor IC1331 is
instructed to generate its own sync signal so that the screen back-
ground becomes blue and the OSD can still be used. Level at CIC1401-
(19) is < 3.2V.
All control of the OSD is effected via the SDA, SCL and CS
STR 600 AP
I
2
C Bus
Low Pass
Filter
PAL
De-emphasis
18
15
30
31
-
+
-1
Video Matrix
-6dB
PAL
Invert
BASEBAND
NORMAL
DECODER
VCR
TV
Black Level
Adjust
7
8
To Decoder
SCART
OSD_CS
On Screen
OSD_SCK
Display
OSD_SDA
from CIC1400
To TV SCART
is fed out from CIC1401-(38) and
respectivley are fed through the
TVOUT
" are clamped at a predetermined
leads.
OSD
GRUNDIG Service
9
AVIN 2
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