STV82X6 datasheet(13/95 Pages) STMICROELECTRONICS

13 / 95 page

13/95

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.

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

Table 4: A2 System Transmission Modes

System Mode

ZWT-STAT

[2:0]

FM Dematrix

De-emphasis

CH_LANG

[1:0]

Sound

Selection

Sound

Backup

German Zweiton Mono

100

L,R

50 µs

FM Mono

German Zweiton Stereo

110

(L+R)/2,R

50 µs

FM Stereo

FM Mono

German Zweiton Dual

Mono (CH1=A, CH2=B)

101

L,R

50 µs

FM Mono A

FM Mono B

Mute

Korean Zweiton Mono

100

L,R

75 µs

FM Mono

Korean Zweiton Stereo

110

(L+R)/2,(L-R)/2

75 µs

FM Stereo

FM Mono

Korean Zweiton Dual Mono

(CH1 = A, CH2 = B)

101

L,R

75 µs

FM Mono A

FM Mono B

Mute

Zweiton undefined

0XX or 111

L,R

50 µs

FM Mono

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