U4255BM-M Datasheet, PDF (12/32 Pages) ATMEL Corporation – AM / FM RECEIVER IC

MPX Output
The output of the AM demodulator (AM mode) or the output of the FM demodulator
(FM/WB mode) are available at the MPX output (Pin 11).
The MPX output signal can be muted by setting Bit 7 to 1.
The bandwidth of the lowpass filter at the MPX output can be set by means of Bit 79 to
90 kHz or 180 kHz.
Table 20. MPX Output Mute
MPX Output
MPX out, Pin 11 normal operation
Mute ON
Bit 7
0
1
Table 21. MPX Output Bandwidth
Bandwidth MPX Lowpass Filter
90 kHz
180 kHz
Bit 79
0
1
Receiving Condition
Analyzer
The U4255BM-M implements several sensors that provide information about the receiv-
ing condition of the selected station.
Field Strength Sensor
The field strength sensor provides a DC voltage at Pin 9 which represents the logarith-
mic field strength of the signal in the reception band.
The field strength information can be retrieved either from a level detector at the input of
the 2^nd mixer (Pin 26) or from the IF-AGC depending on the setting of Bit 80. The band-
width of the field strength detection in the AGC is smaller than by using the level
detector because of additional selectivity between the 2^nd mixer and the 2^nd IF amplifier
particularly in AM and WB, but the field strength detection in the AGC is limited to the IF
AGC range. Usually the field strength from the level detector is used in FM mode and
the AGC field strength is used in AM mode.
Table 22. Field Strength Selection
Field Strength Narrow Band / Wide Band
Fieldstrength at Pin 26 (wide band)
Fieldstrength from IF-AGC (narrow band)
Bit 80
0
1
Search Stop Detector
A search stop detector is available in AM and FM/WB mode. A STOP condition is
signaled if the frequency of the ZF signal is within a window around the center frequency
of 450 kHz. The width of this search stop window can be set by Bit 85 to 87 in the range
of 0.5 kHz to 80 kHz. The frequency of the ZF signal is measured by counting the num-
ber of periods of the ZF signal during a measurement time which is determined by Bit 73
to 78. The inverted STOP signal is available at Pin 21 according to Table 25. The fre-
quency of 10.25 MHz at Pin 22 is used as time reference.
12 U4255BM-M
4519C–AUDR–07/02