TDA7541B Datasheet, PDF (30/77 Pages) STMicroelectronics – AM/FM car radio tuner IC with stereo decoder and intelligent selectivity system

Functional description
TDA7541B
4.1.5
Note:
4.1.6
Table 12. ISS control modes
Input signals
Mode1
ac ac+ sm dev dev+ inton int80 Function inton
0
0
0
0
0
0
0
wide
0
0
0
0
1
0
0
0
wide
0
0
0
0
1
1
0
0
wide
0
0
0
1
0
0
1
1
narrow
1
0
0
1
1
0
0
0
wide
1
0
0
1
1
1
0
0
wide
0
1
0
0
0
0
1
1
narrow
1
1
1
0
0
0
1
1
narrow
1
1
0
0
1
0
1
0
mid
1
1
1
0
1
1
1
0
mid
1
Mode2
int80 Function
0
wide
0
wide
0
wide
1
narrow
0
mid
0
wide
0
mid
1
narrow
0
mid
1
narrow
Strong adjacent channel correction
Under strong adjacent channel it is possible to have disturbance of the audio signal created
by interference between ISS filter control (deviation detection) and adjacent channel mute.
The control bits SACCE and SACCT can be used to avoid this disturbance. If the function is
activated (SACCE = “1”) the IF counter together with the internal field strength is used to
suppress a malfunction of deviation detection. The bit SACCT is changing the sensitivity of
the SACC block (SACCT = “1” means higher sensitivity).
Figure 10 shows the ISS block diagram including the SACC function.
The IF counter must be switched ON if this function is used (Addr25D4 = “1”)
Weak signal mute
The filtered field strength signal (FSWO) is the reference for soft slope mute control in weak
signal condition to eliminate audible effects. The start point and mute depth are
programmable (WMTH, WMD) in a wide range. These settings together with FSWO bits are
influencing the weak signal mute behavior. The time constant is defined by external
capacitance at PIN 42. Additional adjacent channel mute function is supported. A high pass
filter with -3 dB threshold frequency of 100 kHz, amplifier and peak rectifier generates an
adjacent noise signal from Demodulator output. This value is compared with adjustable
threshold (ACMTH). For present strong adjacent channel the MPX signal is additional
attenuated (ACMD) and has the same time constant as weak signal mute.
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Doc ID 16048 Rev 1