TDA7410ND datasheet(20/34 Pages) STMICROELECTRONICS

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Description of stereodecoder

TDA7410ND

20/34

6.4

PLL and pilot tone detector

The PLL has the task to lock on the 19kHz pilotone during a stereo transmission to allow a

correct demodulation. The included detector enables the demodulation if the pilot tone

reaches the selected pilottone threshold VPTHST. Two different thresholds are available.

The detector output (signal STEREO, see block diagram) can be checked by reading the

status byte of the TDA7410ND via I2C bus.

6.5

Fieldstrength control

The fieldstrength input is used to control the highcut and the stereoblend function. In

addition the signal can be also used to control the noiseblanker thresholds.

6.6

LEVEL input and gain

To suppress undesired high frequency modulation on the highcut and stereoblend function

the LEVEL signal is lowpass filtered firstly. The filter is a combination of a 1st order RC

lowpass at 53kHz (working as anti-aliasing filter) and a 1st order switched capacitor lowpass

at 2.2kHz. The second stage is a programmable gain stage to adapt the LEVEL signal

internally to different IF. The gain is widely programmable in 16 steps from 0dB to 10dB

(step = 0.67dB).

6.7

Stereoblend control

The stereoblend control block converts the internal LEVEL voltage (LEVEL INTERN) into an

demodulator

compatible analog signal which is used to control the channel separation between 0dB and

the maximum separation. Internally this control range has a fixed upper limit which is the

internal reference voltage REF5V. The lower limit can be programmed to be 33%, 42%, 50%

or 58% of REF5V (see Figure 13, 14).

Figure 13.

Internal stereoblend characteristics

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

012

LEVELINTERN [V]

CS [dB]

345

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