TDA8205 Datasheet, PDF (3/8 Pages) STMicroelectronics – NICAM QPSK DEMODULATOR

TDA8205
carrier without disruption due to the modulation.
Dual frequency operation is made possible by syn-
thesising the carrier reference frequency thus sav-
ing the need for two extra crystals. Dual VCXO can
also be software selected (SYN bit of CR3 in
TDA8204) with external crystal (Pin XC1/XC2) for
new standards. Selection between XC1 and XC2
is done with bit "IBG" in CR3 register of TDA8204
(IBG = 0 XC1 selected, IBG = 1 XC2 selected).
The standards switch controls operation of the
QSPK demodulator at either 6.552MHz or
5.85MHz. This can be controlled via the I²C bus or
the decoder set into automatic mode in which it
determines the standard by alternately trying to
lock to the two systems.
On chip low pass filters recover the in-phase and
quadrature data channels which are then sliced by
comparators. The symbol clock is recovered from
this data and used to sample and re-time it. The
two data channels are then decoded and serialized
to obtain the NICAM-728 data which is then passed
on to the NICAM decoder in the TDA8204.
After processing the NICAM into a digital bit-stream
in the TDA8204, the data is passed back to the
TDA8205 for the analog functions of the DACs to
be performed.
Conversion of the pulse width modulated bit
streams to analog takes place and is followed by
low pass filtering which removes high frequency
quantising noise and performs J-17 de-emphasis.
The DACs signal level can be adjusted to match
the reserve sound signal level.
1VRMS maximum on Pins LFIL1/RFIL1 can be ob-
tained by selection of appropriate resistor on
Pin RG.
Once the analog audio has been recovered, certain
source switch functions are performed. If the NI-
CAM signal fails and if the reserve sound flag (C4),
of SRO register, is set the reserve sound switch
automatically selects Mono Audio Input. If the re-
serve sound flag (C4) is reset, the reserve sound
switch will not change and the audio outputs will be
muted (DAC outputs muted).
If the NICAM signal only carries data, Mono Audio
Input is selected. The reserve sound switch can be
forced to select Mono Audio Input via I²C bus, using
Bit FS0 = 1 and FS1 =0 of CR3 Register.
This can be used in the case of NICAM marginal
reception. To select Stereo Left and Right Audio
Input Bit FS0 = 0 and FS1 = 1 of CR3 Register must
be selected. The outputs from this reserve sound
switch are available on Audio mutable output left
and right, and are internaly connected to the audio
matrix.
A simple audio switching matrix is provided inter-
nally for flexible control over the audio source and
destination selection.
Audio signal left and right coming from the reserve
sound switch and the external audio input left and
right can be switched to the audio outputs left and
right .
DAC and auxiliary audio outputs can be muted. An
additional +6dB gain can be applied to raise the
output levels to 2VRMS maximum. For more infor-
mation see Software Specification chap-
ter (III.5.3/TDA8204).
The DAC outputs are automatically muted under
the following conditions
- loss of frame alignement
- the bit error rate (Ber) is > error rate limit
- NICAM signal is conveying M1 only. The right
DAC is muted unless M1 has been selected to be
on both DAC outputs.
- NICAM signal is conveying data only.
For test purposes, the DAC outputs can be un-
muted by forcing the bi-directional mute Pin 25 of
TDA8204 or via I²C bus.
ABSOLUTE MAXIMUM RATINGS
Symbol
VCC
VDD
Ptot
Toper
Tstg
Parameter
Supply Voltage
Supply Voltage
Total Power Dissipation
Operating Temperature Range
Storage Temperature Range
Value
15
7
1.2
0, + 70
-20, + 150
Unit
V
V
W
o_C
o_C
THERMAL DATA
Symbol
Rth (j-a)
Parameter
Thermal Resistance Junction-Ambient
Max.
Value
67
Unit
o_C/W
3/8