TDA7402 Datasheet, PDF (38/59 Pages) STMicroelectronics – CARRADIO SIGNAL PROCESSOR

TDA7402
5.0 FUNCTIONAL DESCRIPTION OF THE MULTIPATH-DETECTOR
Using the Multipath-Detector the audible effects of a multipath condition can be minimized. A multipath-condi-
tion is detected by rectifying the spectrum around 19kHz in the fieldstrength signal. An external capacitor is used
to define the attack- and decay-times for the Stereoblend (see blockdiagram, fig. 32). Due to the very small
charge currents this capacitor should be a low leakage current type (e.g ceramic). Using this configuration an
adaptation to the user’s requirement is possible without effecting the ”normal” fieldstrength input (LEVEL) for
the stereodecoder. This application is given in fig. 32. Another (internal) time constant is used to control the
Highcut through the multipath detector
Selecting the ”internal influence” in the configuration byte the Stereo-Blend and/or the Highcut is automatically
invoked during a multipath condition according to the voltage appearing at the MP_OUT-pin.
Figure 32. Blockdiagram of the Multipath-Detector
6.0 QUALITY DETECTOR
The A619 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 :
V_Qual = 1.6 (V_Noise-0.8 V)+ a (REF5V-V_Mpout).
The noise-signal is the PEAK-signal without additional influences (see noiseblanker description). The factor ’a’
can by programmed to 0.7 .... 1.15. The output is a low impedance output able to drive external circuitry as well
as simply fed to an AD-converter for RDS applications.
7.0 TESTMODE
During the Testmode, which can be activated by setting bit D₀ and bit D₁ of the stereodecoder testing-byte, sev-
eral internal signals are available at the FD2R+ pin. During this mode the input resistance of 100kOhm is dis-
connected from the pin. The internal signals available are shown in the Data-byte specification.
38/59