TDA7513 datasheet(24/58 Pages) STMICROELECTRONICS

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TDA7513

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recommended value. The 4th order input filter has a corner frequency of 80kHz and is used to attenuate

spikes and nose and acts as an anti aliasing filter for the following switch capacitor filters.

Demodulator

In the demodulator block the left and the right channel are separated from the MPX signal. In this stage

the 19 kHz pilot tone is cancelled.

To reach a good channel separation the device offers an I2C bus programmable roll-off adjustment which

is able to finely compensate for the low-pass behaviour of the tuner section. An adjustment to better than

40dB channel separation is possible. The bits for this adjustment are located ogether with the fieldstrength

adjustment in one byte. This gives the possibility to perform an optimization step during the production of

the carradio where the channel separation in relation to the fieldstrength control are trimmed.

The setup of the Stereoblend characteristics, which is programmable in a wide range, is de-scribed in 2.8.

De-emphasis and Highcut.

One filter is provided to realize de-emphasis and High-Cut filtering.

The lowpass filter for the de-emphasis allows to choose between a time constant of 50

µs and 75µs.

The filter time constant can further be controlled in both cases over the range = 2 DEEMPH. The control

is automatically performed as a function of the filtered field strength level: inside the highcut control range

(between VHCH and VHCL) the level is converted into a 5 bit word which drives the lowpass time constant.

The FM highcut function can be switched off by I2C bus (bit 0,of APSD data byte 11). The setup of the

highcut characteristics is described in 2.9.

In AM the high-cut filter can be programmed (bit 3 to 7 of APSD data byte 16) to a fixed value (inside the

above-mentioned programmable range) in order to provide the desired lowpass characteristic of the AM

signal.

PLL and Pilot Tone Detector

The PLL is tasked with locking on the 19kHz pilot tone during a stereo transmission to allow the correct

demodulation. The detector enables the stereo demodulation if the pilot tone reaches the selected pilot

tone threshold VPTHST. Two different thresholds are available. The detector output can be checked by

reading the status byte of the TDA7407 via I2C bus.

Fieldstrength Control

The filtered field strength signal is fed to the stereo decoder where it can be finely adjusted and normalized

so that it can be used to control the highcut and stereoblend functions. Furthermore the adjusted signal

can also be used to control the noise-blanker thresholds. The unfiltered field strength meter, on the other

hand, is used as input for the stereo decoder multipath detector. These additional functions are described

in sections 3.3 and 4.

LEVEL Input and Gain

To help suppress undesired high frequency modulation of the highcut and stereoblend functions the tuner

filtered field strength signal (LEVEL) is lowpassed by a combination of a 1st order RC low-pass at 53kHz

(working as anti-aliasing filter) and a 1st-order switched capacitor lowpass at 2.2kHz.

The second stage is a programmable gain stage to finely adapt the LEVEL signal internally against tuner

spread (see Testmode section 5 LEVELINTERN). The gain is widely programmable in 16 steps from 0dB

to 10dB (step = 0.67dB).

Stereoblend Control

The stereoblend control block converts the internal LEVEL voltage (LEVELINTERN) into a demodulator-

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