U4255BM-M Datasheet, PDF (15/32 Pages) ATMEL Corporation – AM / FM RECEIVER IC

Multipath Sensor
U4255BM-M
Table 28. Output Voltage of Adjacent Channel Sensor for Different Receiving
Conditions and Center Frequencies
Adjacent Channel Disturbance
300 kHz
450 kHz
600 kHz
no
high
low
high
below
high
high
low
above
low
high
high
The multipath sensor is active in FM mode only and measures the disturbance due to
multipath reception. The multipath sensor detects drops in the field strength after the
integrated band filter by calculating the difference between an averaged maximum field
strength and the current field strength. The maximum depth of these drops is repre-
sented by the voltage of the peak detector at Pin 40 (MULTIP). The level of this voltage
represents the degree of disturbance in the received signal.
Figure 9. Multipath Sensor
+
4k
Pin40
A Multipath Noise Canceller (MNC) is implemented to reduce disturbance of the
received signal in multipath reception conditions. If the difference between the momen-
tary and the averaged field strength falls below a threshold adjustable by Bit 81 to 84
(see Table 30), the MPX signal may be muted and this situation (MPINT) can be signal-
ized at Pin 21 (INT) according to Table 25. Muting of the MPX signal during multipath
disturbances can be activated be setting Bit 8.
Table 29. Multipath Noise Canceller
Multipath Noise Canceller
Active
Not active
Bit 8
0
1
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4519C–AUDR–07/02