TDA7411 datasheet(28/43 Pages) STMICROELECTRONICS

28 / 43 page

TDA7411

28/43

Figure 23. Block Diagram of Multi path Detector

Programming

To obtain a good multipath performance an adaptation is necessary. Therefore the 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.

Quality Detector

The A673 offers a quality detector output, which gives a voltage representing the FM-reception conditions.

To calculate this voltage the MPX-noise and the multipath-detector output are summed according to the

following formula:

VQual = 1.6 (VNoise-0.8 V)+ a (REF5V-VMpout).

The noise-signal is the PEAK-signal without additional influences (see noise blanker description). The fac-

tor 'a' can by programmed from 0.6 to 1.05. The output is a low impedance output able to drive external

circuitry as well as simply fed to an AD-converter for RDS applications.

AF Search Control

The TDA7411 is supplied with several functionality to support AF-checks using the stereo decoder. As

mentioned already before the high impedance mute feature avoids any clicks during the jump condition.

It is possible at 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-constant.

One additional pin (AFS) is implemented in order to separate the audio processor-mute and stereo decod-

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

shown (please not the pins FAS and SM are active low as well as all control-bits indicated by an over bar).

TDA7411 データシート(PDF) 28 Page - STMicroelectronics