TDA7402 datasheet(41/71 Pages) STMICROELECTRONICS

41 / 71 page

TDA7402

Functional description of stereo decoder

41/71

Figure 29.

Signals during stereo decoder's SoftMute

Figure 30.

Signal control via SoftMute pin

6.2

InGain + infilter

The InGain stage allows adjustment of the MPX-signal to a magnitude of about 1Vrms

internally, which is the recommended value. The 4th order input filter has a corner frequency

of 80kHz and is used to attenuate spikes and noise, and acts as an anti-aliasing filter for the

following switch capacitor filters.

6.3

Demodulator

In the demodulator block, the left and the right channels are separated from the MPX signal.

In this stage the 19kHz pilot tone is cancelled. To reach a high channel separation the A619

offers an I2C bus programmable roll-off adjustment which is able to compensate for the

lowpass behavior of the tuner section. If the tuner's attenuation at 38kHz is in a range from

7.2% to 31.0%, the A619 needs no external network in front of the MPX-pin. Within this

range, an adjustment to obtain at least 40dB channel separation is possible. The bits for this

adjustment are located together with the fieldstrength adjustment in one byte. This gives the

possibility to perform an optimization step during the production of the car radio, where the

MP-HOLD

SOFTMUTE

D00AU1165

SOFTMUTE

PLL-HOLD

INFLUENCE

STDHMUTE

MUTED

STDHMUTE

INFLUENCE

SOFTMUTE

INFLUENCE

IIC-BUS

SOFTMUTE

INFLUENCE

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