E-TDA7461NDTR 데이터 시트보기 (PDF) - STMicroelectronics

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E-TDA7461NDTR

Car radio signal processor

STMicroelectronics 

TDA7461

Stereo decoder part

4.6.4

Because of the overlap of this range and the range of the stereo/mono transition it can be

controlled by stereo blend. This threshold increase is programmable in 3 steps or switched

off with bits D0 and D1 of the fieldstrength control byte.

Over deviation detector

If the system is tuned to stations with a high deviation the noise blanker can trigger on the

higher frequencies of the modulation. To avoid this wrong behavior, which causes noise in

the output signal, the noise blanker offers a deviation dependent threshold adjustment. By

rectifying the MPX signal a further signal representing the actual deviation is obtained. It is

used to increase the PEAK voltage. Offset and gain of this circuit are programmable in 3

steps with the bits D6 and D7 of the stereo decoder byte (the first step turns off the detector,

see Figure 18).

4.7

Functional description of the multipath detector

Using the internal detector the audible effects of a multipath condition can be minimized. A

multipath condition is detected by rectifying the 19 kHz spectrum in the fieldstrength signal.

Selecting the "internal influence" in the configuration byte, the channel separation is

automatically reduced during a multipath condition according to the voltage appearing at the

MPOUT pin.

To obtain a optimal performance an adaptation is necessary. Therefore the gain of the

19 kHz bandpass is programmable in four steps as well as the rectifier gain. The attack and

decay times can be set by the external capacitor value.

4.8

Test mode

During the test mode which can be activated by setting bit D0 of the testing byte and bit D5

of the subaddress byte to "1" several internal signals are available at the CASSR pin. During

this mode the input resistance of 100 kΩ is disconnected from the pin. The internal signals

available are shown in the software specification.

Figure 26. Block diagram of the multipath detector

LEVEL

VDD

DC=1μA

to SB

-

int. INFLUENCE

MPIN

BANDPASS

19KHz

RECTIFIER

GAIN

2 BITS

GAIN

2 BITS

MPOUT

220nF

D97AU880

31/48

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