TDA7513T_07 Datasheet, PDF (28/84 Pages) STMicroelectronics – Single chip FM/AM tuner with stereo decoder and audio processor

Functional description
TDA7513T
3.1.6
3.1.7
3.1.8
3.1.9
3.1.10
content of the fieldstrength signal. The multipath detector influence on the adjacent channel
detector is selectable by I²C bus (MPOFF). The multipath information after filtering and
rectification is available as analog output on pin #TUNQUALITY (the gain can be selected
via I²C bus) in combination with the adjacent channel content information. It is possible to
enable multipath content information output only via I²C bus control.
450kHz IF narrow bandpass filter (ISS filter)
The device features an additional automatically selectable IF narrow bandpass filter for
suppression noise and adjacent channel signals. This narrow filter has three switchable
bandwidth positions: narrow range (80kHz), mid range (120kHz) and weather band (30kHz).
WHen the ISS filter is not inserted the IF bandwidth (wide range) is defined only by the
ceramic filter chain. The filter is switched in after mixer2 before the 450kHz limiter stage.
The centre frequency can be finely adjusted (AISS) by software.
Deviation detector
In order to avoid excessive audio distortion the narrow ISS filter is switched OFF when
overdeviation of the incoming signal is detected. The demodulator output signal is low-pass
filtered and rectified to generate a DC level in an external capacitor through a software-
controlled current (TDEV). This level is compared with a programmable threshold (DWTH,
DTH) comparator (comparator3) to generate two digital signals (dev, dev+).
ISS switch logic
All digital signals coming from adjacent channel detector, deviation detector and softmute
are combined in a decision matrix to generate the control signals for the ISS filter switch.
The IF bandpass switch mode can be also controlled by software (ISSON, ISS30, ISS80,
ISSCTL). The switch-on of the IF bandpass can be further controlled from the outside by
manipulation of the voltage at pin #ISSTC. Two application modes are available (APPM).
The conditions are described in table 1.
Soft mute control
The external fieldstrength signal at pin #SMETERTC is the reference for MPX mute control.
The start point and mute depth are programmable over a wide range. The time constant is
defined by the external capacitor connected to pin #FMMUTETC.
Additionally adjacent channel mute function is supported. A software-configurable highpass
/ bandpass filter centered at about 100kHz followed by an amplifier and a peak rectifier
generates adjacent noise information starting from the MPX output; the information is acted
upon with the same time constant as the softmute by the MPX muting circuit. The adjacent
channel mute starting point, slope and depth are I²C bus programmable.
Station detector and seek stop
A station detection function is provided for easy seek stop operation. The unfiltered
fieldstrength signal is compared with a programmable threshold and the result (logic '1' if the
current station strength is higher than the threshold) is combined by an AND gate with the IF
counter output (logic '1' if the current channel is centered within a programmable window
around the desired frequency). The result is available on pin #SD for direct connection to the
microprocessor. Channel quality assessment for RDS Alternate Frequency operation makes
use of the SD signal in conjunction with analog information on adjacent channel and
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