STV8206 Datasheet, PDF (15/97 Pages) STMicroelectronics – Multistandard TV Audio Processor and Digital Sound Demodulator

STV82x6
Demodulator Block
The level of the demodulated sound may require adjusting in order to compensate for the difference
in levels between the multiple source (NICAM, FM or AM) and standard source (FM deviation wide
range from 15 to 500 kHz) signals. The correct range for all level variations (+24 to -6 dB) is
selected in registers PRE_FM and PRE_NICAM. The internal sound level of the various sources
(FM/AM, NICAM and SCART) is read in registers PEAK_DET_CTRL, PEAK_DET_STATL and
PEAK_DET_STATR before audio processing and can be used to implement Automatic Pre-scaling
via an external I²C interface.
In Automatic mode, the STV82x6 selects and performs all appropriate de-emphasis, dematrixing,
sound selection and mute functions according to the standard and transmission mode detected.
Mono system: Mono audio signals received by an FM or AM carrier are demodulated. Left and
right audio outputs are identical. Automatic mute is applied when the mono standard cannot be
identified.
A2 systems (or Zweiton): Transmission of mono, stereo or bilingual audio signals using 2 separate
FM carriers + identification pilot. The pilot, transmitted by the second carrier, can be modulated by
two different tones in order to define Stereo or Dual-Mono mode. If not modulated, only the mono
signal is broadcast on the first carrier. Zweiton mode is read in register ZWT_STAT and described in
Table 4. In the event of poor signal detection, the audio output is switched back to FM Mono mode
(backup). In Dual Mono mode, the language (A on Channel 1, B on Channel 2) can be selected
separately for each audio output channel (Loudspeaker, Headphone, SCART or I²S) in register
CH_LANG.
Table 4: A2 System Transmission Modes
System Mode
ZWT-STAT
[2:0]
FM Dematrix
FM
De-emphasis
CH_LANG
[1:0]
German Zweiton Mono
100
L,R
50 µs
XX
German Zweiton Stereo
110
(L+R)/2,R
50 µs
XX
German Zweiton Dual
Mono (CH1=A, CH2=B)
101
L,R
50 µs
01
10
Korean Zweiton Mono
100
L,R
75 µs
XX
Korean Zweiton Stereo
110
(L+R)/2,(L-R)/2
75 µs
XX
Korean Zweiton Dual Mono
(CH1 = A, CH2 = B)
101
L,R
75 µs
01
10
Zweiton undefined
0XX or 111
L,R
50 µs
XX
Sound
Selection
FM Mono
FM Stereo
FM Mono A
FM Mono B
FM Mono
FM Stereo
FM Mono A
FM Mono B
FM Mono
Sound
Backup
X
FM Mono
X
Mute
X
FM Mono
X
Mute
X
Note:
A2 and A2* standards are German Zweiton, while A2+ is Korean Zweiton.
NICAM systems: Transmission of mono, stereo, bilingual or trilingual audio signals using a
modulated-QPSK carrier and an FM/AM sound carrier backup. The digital QPSK modulation
broadcasts either channel stereo, dual mono, mono + data or data only. The selected NICAM mode
is read in register NICAM_STAT and described in Table 5. In the event of high bit-error rates, the
audio output is automatically switched back to the reserve sound transmission (FM/AM Mono) or
muted if there is no backup. In Dual Mono or Stereo mode with no backup, the language can be
selected separately for each audio output channel (Loudspeaker, Headphone, SCART or I²S) in
register CH_LANG.
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