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ATR4258 Datasheet(PDF) 13 Page - ATMEL Corporation |
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ATR4258 Datasheet(HTML) 13 Page - ATMEL Corporation |
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13 / 38 page ![]() 13 4838B–AUDR–05/05 ATR4258 4.15 Integrated FM Band Filter For FM reception a band filter with variable bandwidth is integrated in front of the demodulator to provide channel selectivity on the 2 nd IF. The bandwidth of this filter can be adjusted by bit 0 to 3 (see Table 4-18) to be suitable for the present receiving condition. In WB mode, the bandwidth of the integrated filter is shifted to lower bandwidth values, while the necessary channel selectiv- ity is achieved by an external ceramic filter. The center frequency of the integrated FM band filter can be adjusted by means of bit 14 to 17. The field strength after the integrated FM band filter that is available at pin 20 (bit 55 = 1) can be used for this purpose. 4.16 FM Demodulator For weather band reception, the gain of the FM demodulator is increased and can be adjusted by means of bit 71 and bit 72 in order to increase the output voltage to compensate the low fre- quency deviation in weather band. An integrated demodulator fine adjustment allows automatic fine tuning of the demodulator cen- ter frequency to the average frequency of the received signal. This feature is implemented for use in weather band mode and can be activated by setting bit 53 to 0. Figure 4-3. FM Demodulator Automatic Fine Tuning Table 4-18. Bandwidth of the Integrated Band Filter IF Bandwidth FM (kHz) IF Bandwidth WB (kHz) Bit 3 Bit 2 Bit 1 Bit 0 220 195 0 0 0 0 ... ... ... ... ... ... 200 160 0 0 1 1 ... ... ... ... ... ... 165 120 0 1 1 0 ... ... ... ... ... ... 130 80 1 0 0 1 ... ... ... ... ... ... 90 45 1 1 0 0 80 Not usable 1 1 0 1 70 Not usable 1 1 1 0 60 Not usable 1 1 1 1 FM Demod + AM AGC B92 Center freq. Bit 53 Automatic frequency adjustment MPX (Pin 11) IFAGCH (Pin 35) V3P (Pin 27) |
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