tda7513t STMicroelectronics, tda7513t Datasheet - Page 38

• Manufacturer Part Number: tda7513t
• Description: Single-chip Fm/am Tuner With Stereo Decoder And Audio Processor
• Manufacturer: STMicroelectronics

Functional description
3.6.2
3.7
3.7.1
3.8
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cases the behavior of the noiseblanker can be improved by increasing the threshold even in
a region of higher fieldstrength. Sometimes a wrong triggering occures for the MPX signal
often shows distortion in this range which can be avoided even if using a low threshold.
Because of the overlap of this range and the range of the stereo/mono transition it can be
controlled by stereoblend.
This threshold increase is programmable in 3 steps or switched off.
Over deviation detector
If the system is tuned to stations with a high de-viation the noiseblanker might be
erroneously triggered on the higher frequencies of the modulation. To avoid this
unnecessary muting of the signal, the noiseblanker offers a deviation-dependent threshold
adjustment.
By rectifying the MPX signal a further signal representing the actual deviation is obtained.
This is used to increase the PEAK voltage. The circuit offset, gain (and enabling) are
programmable in 3 steps.
Multipath detector
Using the stereo decoder multipath detector the audible effects of a multipath condition can
be minimized. A multipath condition is detected by rectifying the 19kHz spectrum in the
fieldstrength signal. An external capacitor is used to define the attack and decay times (see
Figure
and the MPIN signal is internally connected to the unfiltered field strength. To avoid losing
the information stored in the external capacitor during AF checks but at the same time to
allow some fast multipath detection capability during the same AF check period, the external
capacitor is disconnected by the MP-Hold switch. This switch is controlled directly by the pin
#RDSMUTE.
Moreover, 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 pin #MULTIPATHTC.
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 properly choosing the value of the external capacitor.
Quality detector
The device offers a quality detector output voltage representing the quality of the FM
reception conditions. This voltage is derived from MPX noise information and multipath
information according to the following formula:
The noise signal is the PEAK signal of the noise blanker without additional influences. The
multipath information weight "a" can be programmed between 0.7 and 1.15. The circuit
output pin #QUALITY is a low impedance output able to drive external circuitry as well as
suitable to be simply fed to an A/D converter for RDS applications.
20). The pin #MULTIPATHTC is externally connected to a capacitor of about 47nF
Quality = 1.6 (V
noise
-0.8V)+ a (REF5V- V
MPOUT
)
TDA7513T