
FUNCTIONAL DESCRIPTION
Ascanbe seenfromthe blockdiagram,theinputto
the demodulatorsection is selectable from one of
twoI.F.sourcesviathe I
2
Cbus.Theselectedsignal
is then passed through an AGC block, having a
range of 28dB, before being digitised in the
ADC unit.Asinglequartzcrystal(suggestedvalue:
between24.712MHzand27MHz)is usedforthe all
thedigitalprocessing,includingdemodulation,iden-
tification, control, filtering. This has the advantage
ofasingleclocksignalsourceforthewholeICwhich
eliminates problems of multiple clock. The single
clock canbe chosento minimize interferencein the
TVIF andRF stagesof the tunersystem.
Thedemodulatorsystemcan identifyand demodu-
lateallthestandarddescribedintheTable1. There-
sult of the recognition is flagged up to the host
system viathe I
2
C buscommunication system.
In the case of NICAM transmissions, in the event
of a failure of the receivedsignal or a degradation
of thebiterror rate (BER)belowa prescribedlevel,
thesystem will automaticallydefault to the reserve
soundtransmission on mono FM or AM.
For FM demodulation, the discriminator can nor-
mallyhandlesignalshaving250kHzdeviation.This
covers all European standards, and ensure an
optimized compromise for the signal to noise ratio
inonehand,andovermodulationintheotherhand.
However, it is possible to extand the deviation
rangeupto 500kHz(I
2
C programmable)in orderto
coverrequestsof some broadcasters.
Fully automatic standard recognition and setting
can be achieveusing simple routines.
Figure 1 :
AudioMatrix
Appropriate de-emphasis networks in the digital
domain are applied to the resulting demodulated
signals (50
μ
s, J17), followed by dematrixing if re-
quired. The digital datastream is then passed
through 2 x 16bitsDACs beforethe audio matrix.
All thisfirst section is working at 3.3V thanksto an
integratedvoltageregulator.In stand-bymode,the
voltage regulator pulls the voltage down to zero,
ensuringno power dissipation in this part.
An audio matrix allows the selection of inputs ap-
pliedontheoutputsSCART1,SCART2andMONO
accordingto the diagramshown in Figure1.
The ”MOUT”outputs either the signal L1, or R1 or
(L1+R1)/2.Thisallowstorecordtheselectedchan-
nel in monomode, for exampleon thelinear chan-
nel of a VCR simultanously with the stereo mode.
Maximumoutput swing is 1V
RMS
.
The audiomatrixsectionhas its ownpower supply
regulator, allowing to keep this part working even
when therest is in stand-bymode. Thisachievesa
”THRU” mode from input ”SCART1” to output
”SCART2”andinput”SCART2”tooutput”SCART1”.
The maximum output swing of both SCART1 and
SCART2 is 2V
RMS
.
Remark : Circuit operationis possible with only a
single 5V supply.In this case, the AV
CC
supplypin
is connectedto 5V.Maximum output swing is then
limitedto 1V
RMS
anda 6dBattenuationis automat-
ically added to the DAC output. In that case, the
resistorshownas R2 = 39
in theApplicationDia-
gram (betweenPin 8 and Pin 21) must be replace
by a short circuit to avoid clipping.
MUTE
MUTE
L1,R1,
(L1 + R1)/2
SELECTOR
MOUT
AO1(SCART1)
MUTE
DAC
MIN
LI1(SCART1)
2
2
2
2
2
S1
S2
GAIN
±
6dB
LI2(SCART2)
AO2(SCART2)
L1/R1
L2/R2
8
STV8203
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