U4255BM-M Datasheet, PDF (14/32 Pages) ATMEL Corporation – AM / FM RECEIVER IC

Adjacent Channel
Sensor
The adjacent channel sensor is active in FM mode only and measures the field strength
outside the reception band. By setting the center frequency of the band filter of the adja-
cent channel sensor below or above the 2^nd IF frequency (Bit 5, Bit 6), it can be
determined whether the disturbance signal is located above or below the reception fre-
quency (see Table 28). The bandwidth of the band filter used in the adjacent channel
sensor can be changed by means of Bit 10 to 13. If Bit 4 = 0 the default bandwidth set-
ting is used. The output of the adjacent channel sensor is independent of the bandwidth
setting of the integrated FM band filter.
Figure 8. Adjacent Channel Sensor
IF
intergr. FM bandfilter
+
-
+
log
log
4k
50k
Pin 10
Table 26. Bandwidth of the Adjacent Channel Detector Filter
BW Adjustment
Bit 13
Bit 12
3 kHz
0
0
16 kHz
0
0
32 kHz
0
1
50 kHz
0
1
65 kHz
1
0
80 kHz
1
0
95 kHz
1
1
110 kHz
1
1
50 kHz
0
0
65 kHz
0
0
80 kHz (default)
0
1
95 kHz
0
1
110 kHz
1
0
130 kHz
1
0
145 kHz
1
1
160 kHz
1
1
Bit 11
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Bit 10
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
Table 27. Center Frequency Adjacent Channel Sensor
Center Frequency
Bit 6
450 kHz
0
300 kHz
0
700 kHz
1
Filter OFF
1
Bit 5
0
1
0
1
14 U4255BM-M
4519C–AUDR–07/02