ATR4255 datasheet(13/32 Pages) ATMEL

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ATR4255

4837A–AUDR–10/04

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 bit 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.

Receiving Condition

Analyzer

The ATR4255 implements several sensors that provide information about the receiving

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 2nd 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.

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 bit 87 in the

range of 0.5 kHz to 80 kHz. The frequency of the ZF signal is measured by counting the

number of periods of the ZF signal during a measurement time which is determined by

bit 73 to bit 78. The inverted STOP signal is available at pin 21 according to Table 25 on

page 14. The frequency of 10.25 MHz at pin 22 is used as time reference.

Table 20. MPX Output Mute

MPX Output

Bit 7

MPX out, pin 11 normal operation

Mute ON

Table 21. MPX Output Bandwidth

Bandwidth MPX Lowpass Filter

Bit 79

90 kHz

180 kHz

Table 22. Field Strength Selection

Field Strength Narrow Band/Wide Band

Bit 80

Fieldstrength at pin 26 (wide band)

Fieldstrength from IF-AGC (narrow band)

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