TDA7412 datasheet(31/56 Pages) STMICROELECTRONICS

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TDA7412

Figure 24. Signals during stereodecoder's SoftMute

Figure 25. Signal-Control via SoftMute-Pin

3.2 InGain + Infilter

The InGain stage allows to adjust the MPX-signal to a magnitude of about 1Vrms internally which is the recom-

mended value. The 4.th 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.

3.3 Demodulator

In the demodulator block the left and the right channel are separated from the MPX-signal. In this stage also the

19-kHz pilottone is cancelled. For reaching a high channel separation the A679 offers an I2C-bus programmable

roll-off adjustment which is able to compensate the lowpass behavior of the tuner section. If the tuner's attenu-

ation at 38kHz is in a range from 7.2% to 31.0% the A679 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 adjust-

ment are located together with the fieldstrength adjustment in one byte. This gives the possibility to perform an

MP-HOLD

SOFTMUTE

D00AU1165

SOFTMUTE

PLL-HOLD

INFLUENCE

STDHMUTE

MUTED

STDHMUTE

INFLUENCE

SOFTMUTE

INFLUENCE

IIC-BUS

SOFTMUTE

INFLUENCE

TDA7412 Datasheet(PDF) 31 Page - STMicroelectronics