ATR4258 datasheet(13/38 Pages) ATMEL

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ATR4258

4838A–AUDR–10/04

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 2nd IF. The bandwidth of this filter can

be adjusted by bit 0 to 3 (see Table 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 selectivity 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.

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 com-

pensate the low frequency deviation in weather band.

An integrated demodulator fine adjustment allows automatic fine tuning of the demodu-

lator center 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 5. FM Demodulator Automatic Fine Tuning

Table 18. Bandwidth of the Integrated Band Filter

IF Bandwidth FM

IF Bandwidth WB

Bit 3

Bit 2

Bit 1

Bit 0

220

195

...

200

160

...

165

120

...

130

100

...

–

111

–

111

FM Demod

AGC

B92

Center freq.

Bit 53

Automatic

frequency

adjustment

MPX (Pin 11)

IFAGCH (Pin 35)

V3P

(Pin 27)

ATR4258 Datasheet(PDF) 13 Page - ATMEL Corporation

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