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TDA7407D

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configuration an external adaptation to the user's requirement is given in fig.25.

To keep the old value of the Multipath Detector during an AF-jump, the external capacitor can be discon-

nected by the MP-Hold switch. This switch can be controlled directly by the AFS-Pin.

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 MP_OUT pin. A possible application

is shown in fig. 25.

6.8.1 Programming

To obtain a good multipath performance an adaptation is necessary. Therefore tha gain of the 19kHz

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.

6.9

QUALITY DETECTOR

The TDA7407D offers a quality detector output which gives a voltage representing the FM reception con-

ditions. To calculate this voltage the MPX noise and the multipath detector output are summed according

to the following formula:

The noise signal is the PEAK signal without additional influences. The factor "a" can be programmed from

0.7 to 1.15. the output is a low impedance output able to drive external circuitry as well as simply fed to

an A/D converter for RDS applications.

6.9.1 AF Search Control

The TDA7407D is supplied with several functionality to support AF-checks using the stereodecoder. As

mentioned already before the highohmic-mute feature avoids any clicks during the jump condition. It is

possible a the same time to evaluate the noise- and multipath-content of the alternate frequency by using

the Quality detector output. Therefore the multipath-detector is switched automatically to a small time-con-

stant.

One additional pin (AFS) is implemented in order to separate the audioprocessor-mute and stereodecoder

AF-functions. In Figure 24 the block diagram and control-functions of the complete AFS-functionality is

shown (please note that the pins AFS and SM are active low as well as all control-bits indicated by an

overbar).

6.10 TEST MODE

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

dress byte to "1", several internal signals are available at the CASSR pin.

During this mode the input resistor of 100kOhm is disconnected from the pin. The internal signals available

are shown in the software specification.

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