U4255BM-M Datasheet, PDF (8/32 Pages) ATMEL Corporation – AM / FM RECEIVER IC

Table 12. Pin 20 Output Setting
Pin 20
2^nd IF output
Multipath field strength
Bit 55
0
1
Automatic IF Center
Frequency Adjustment
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
10.25MHz
Automatic
Frequency
adjustment
Pin 37
Bit 56...59
center _FM-Demod
freq.
center
+ _freq.
Bit 14...17
center
+ _freq.
Bit 5,6
FM-
bandfilter
adj.channel
Sensor
For fine tuning, the center frequency of all these integrated active filters (band filter,
demodulator and adjacent channel sensor) can be shifted in steps of 6.25 kHz by
means of Bit 56 to Bit 59. Additionally, the center frequency of the band filter can be
adjusted separately by means of Bit 14 to Bit 17 if Bit 4 is set to 1. If Bit 4 is set to 0, the
default setting is used.
Table 13. 2^nd IF Center Frequency
IF Center
Bit 59
450.00 kHz
0
456.25 kHz
0
461.50 kHz
0
Bit 58
0
0
0
Bit 57
0
0
1
Bit 56
0
1
0
468.75 kHz
475.00 kHz
481.25 kHz
487.50 kHz
0
0
1
1
0
1
0
0
0
1
0
1
0
1
1
0
493.75 kHz
450.00 kHz
443.75 kHz
437.50 kHz
0
1
1
1
1
0
0
0
1
0
0
1
1
0
1
0
431.25 kHz
1
0
1
1
425.00 kHz
418.75 kHz
412.50 kHz
406.25 kHz
1
1
0
0
1
1
0
1
1
1
1
0
1
1
1
1
8 U4255BM-M
4519C–AUDR–07/02