ATR4258 Datasheet, PDF (11/38 Pages) ATMEL Corporation – AM/FM RECEIVER IC

ATR4258
2^nd IF Output
The 2^nd IF after the gain-controlled 2^nd IF amplifier is available at pin 20 (bit 55 = 0). In
AM mode, this signal may be used for an external AM stereo decoder. Alternatively, a
signal corresponding to the logarithmic field strength after the integrated FM band filter,
which is used for multipath detection, can be switched to pin 20 by setting bit 55 = 1.
Automatic IF Center
Frequency Adjustment
Table 15. Pin 20 Output Setting
Pin 20
2^nd IF output
Multipath field strength
Bit 55
0
1
Integrated active filters are used in the FM band filter, FM demodulator and adjacent
channel sensor. The center frequency of these filters is automatically adjusted to the
second IF frequency of 450 kHz. The frequency of 10.25 MHz at pin 22 is used as a
reference for this alignment.
Figure 4. Automatic IF Center Frequency Adjustment
Pin 22
10.25 MHz
Automatic
frequency
adjustment
Pin 37
Bit 56...59
Center
FM-Demod
frequency
Center
frequency
Bit 14...17
FM-
band filter
For fine tuning, the center frequency of all these integrated active filters (band filter and
demodulator) can be shifted in steps of 6.25 kHz by means of bit 56 to bit 59. Addition-
ally, the center frequency of the band filter can be adjusted separately by means of
bit 14 to bit 17.
11
4838A–AUDR–10/04