Datasheet > ATR4255P

ATR4255P

更新时间： 2022-02-26 12:20:59

品牌	Logo	应用领域
爱特美尔 - ATMEL		/
页数	文件大小	规格书
34页	386K
描述
FM Double-conversion System

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ATR4255P 数据手册

ATR4255P

Table 3-9.

FM Bandwidth (BW) Mixer 2

Bit 61

Bit 60

FM BW Mixer 2

150 kHz

200 kHz

250 kHz

450 kHz

Note:

The bandwidth also depends on the values of the application circuit.

3.11 2^ndIF Amplifier

In AM and WB mode, the input of the second IF amplifier is pin 28, which is externally connected

to the 2^ndmixer tank through the AM ceramic filter to achieve channel selectivity. During normal

FM operation (bit 54 = 0), the input of the second IF amplifier is connected to the 2^ndmixer out-

put (pin 23 and pin 24) and the integrated FM band filter is used for channel selectivity only. It is

possible to use an additional external filter between the 2^ndmixer tank and pin 28 in FM mode by

setting bit 54 to “1”.

Table 3-10. 2^ndIF Filter in FM Mode

2^ndIF Filter

Internal filter

Bit 54

External and internal filter

3.12 IF-AGC

The IF-AGC controls the level of the 2^ndIF signal that is passed to the AM demodulator input or

the integrated FM bandfilter, and to the 2^ndIF output (pin 20).

Two different time constants of the IF-AGC can be selected by the capacitors at pin 35

(IFAGCH) and pin 36 (IFAGCL). The short time constant (IFAGCL) is used in FM mode and in

AM search mode. The long time constant (IFAGCH) is used for AM reception.

Table 3-11. IF-AGC Time Constant

Mode

FM/WB

Bit 92

Bit 88

IF AGC Time Constant

IFAGCL (fast)

AM reception

AM search

IFAGCH (slow)

IFAGCL (fast)

In FM/WB mode, the output signal of the FM demodulator is applied to pin 35 via a series resis-

tor of about 95 kΩ. This low-pass filtered output signal of the FM demodulator is used for the FM

demodulator fine adjustment, for muting and as a reference for the deviation sensor.

4883B–AUDR–01/06

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