TDA7541B Datasheet, PDF (33/77 Pages) STMicroelectronics – AM/FM car radio tuner IC with stereo decoder and intelligent selectivity system

TDA7541B
Functional description
possibility to perform an optimization step during the production of the car radio where the
channel separation and the field strength control are trimmed.
In addition to that the FM signal can be inverted.
De-emphasis and high cut
The de-emphasis low pass allows to choose between a time constant of 50 µs/75 µs
(DEEMP). The high cut control range will be in both cases T_HC = 2 x T_Deemp. Inside the high
cut control range (between VHCHT and VHCLT) the LEVEL signal is converted into a 5-bit
word, which controls the low pass time constant between T_Deemp...3 x T_Deemp. Thereby the
resolution will remain 5 bits referred to the voltage range between the VHCHT- and minimum
VHCLT-values.
The high cut function can be switched off by I²C-bus.
Figure 3.
Programming of HC filter
High Cut Filter
Time Constant
3*TDeemp
00
11
HCMax
01
TDeemp
V_FSTC* LG
V_HCLT
V_HCHT
In AM mode (FMON = 0) the DEEMP bit together with the AM corner frequency bits (AMCF)
can be used as programmable AM frequency response. The maximum corner frequency is
defined by T_Deemp, the minimum is defined by 3 x T_Deemp For the over all frequency
response it is need to take into account the frequency response of the AF output at
MPXOUT and the Stereo decoder demodulator too.
19 kHz PLL and pilot tone detector
The PLL has the task to lock on the 19 kHz pilot tone during a stereo-transmission to allow a
correct demodulation. The included pilot tone-detector enables the demodulation if the pilot
tone reaches the selected pilot tone threshold VPTHST. Two different thresholds are
available. The status of the detector output can be checked by reading the status byte of the
TDA7541B via I²C bus or by reading the STEREO status at MUX pin23.
Field strength control
The field strength input is used to control the high cut- and the stereo blend-function. In
addition the signal can be also used to control the noise blanker thresholds and as input for
the multipath detector.
Level input and gain
As level input for the stereo decoder is used the FSU voltage (pin 27). Applying a capacitor
at FSTC (pin28) a desired time constant can by reached together with the internal resistor of
Doc ID 16048 Rev 1
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