TDA7513 datasheet(23/58 Pages) STMICROELECTRONICS

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TDA7513

Quality Factor

Figure 12 shows the two possible quality factors (1 and 2) at a center frequency of 1kHz.

TREBLE

There are two parameters programmable in the treble filter stage (see figs 13, 14):

Attenuation

Figure 13 shows the attenuation as a function of frequency at a center frequency of 17.5kHz.

Center Frequency

Figure 14 shows the four possible Center Fre-quencies: 10, 12.5, 15 and 17.5kHz.

AC Coupling

In some applications additional signal manipulations are desired such as surround-sound processing or

more extensive band equalizing. For this purpose a AC-Coupling is placed before the Speaker-attenua-

tors, which can be activated or internally shorted by Bit7 in the APSD data byte 0. The input impedance

of the AC Inputs is 25k

Ω. The external AC coupling is advised for those applications where very low-level

"pop" performance is a must.

Speaker Attenuator

The speaker attenuators have exactly the same structure and range as the Volume stage.

4.5 STEREODECODER

The stereodecoder part of the present device (see Fig. 15) contains all functions necessary to demodulate

the MPX signal such as pilot tone-dependent MONO/STEREO switch as well as "stereoblend" and "high-

cut" functions.

Stereodecoder Mute

The device has a fast and easy-to-control RDS mute function meant for "freezing" the stereo decoder sta-

tus during the RDS AF check time period. When this function is invoked three effects take place:

•1 the stereo decoder input impedance changes to infinity (condition known as high-ohmic input); this

prevents the decoupling capacitor between the pins #TUNER_OUT (tuner output) and #TUNER_IN

(stereo decoder input) to be discharged by a channel with a potentially different DC output for the

duration of the AF check;

•2 the stereo decoder PLL pilot detector is held at the current value;

•3 the external capacitor of the multipath detector used inside the stereo decoder for quality control is

disconnected from the dection circuit in order to make quality checking the AF faster.

The RDS mute is activated from pin #RDSMUTE in AND with Bit 0 of APSD data byte 9.

Stereo Decoder Input stage, Ingain + Infilter

The stereo decoder is crossed by both the FM and the AM signal: the input impedance of the pin

#TUNER_IN is different between the two modes in order to allow the same external coupling components

between #TUNER_OUT and #TUNER_IN to realize different filtering functions. Whilst the input impe-

dence in FM is 100k , in AM the input impedance is decreased to 2k

Ω: this allows the realization of typical

high-pass filters with a corner frequency of 70Hz for AM and less than 5Hz for FM. The low-pass section

of the typical AM transfer function is realized by use of the internal FM High-Cut filter.

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

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