ATR4258 datasheet(9/38 Pages) ATMEL

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ATR4258

4838A–AUDR–10/04

FM 1st IF Amplifier

A programmable gain amplifier is used in FM (and WB) mode between pin 38 and

pin 30 to compensate the loss in the external ceramic band filters. The gain of this

amplifier is adjusted by bit 89 to bit 91. The input and the output resistance is 330

Ω and

fits to external ceramic filters.

Two different temperature coefficients of the FM IF amplifier can be selected by bit 66.

AM 1st IF Amplifier

In AM and WB mode, the gain of the 1st IF amplifier is controlled by the IF-AGC to

extend the control range of the IF-AGC.

2nd Mixer

The 2nd mixer is used in AM, FM and WB mode. The mixer input has 330

Ω input resis-

tance and can be connected directly to an external ceramic filter.

In FM mode, the high output resistance of the second mixer is reduced to increase the

bandwidth of the tank at the mixer output. The output resistance can be selected by

bit 60 and bit 61.

In AM and WB mode bit 61 and bit 62 should be set to 0.

The LO frequency of the 2nd mixer (10.25 MHz) has to be applied at pin 22. This signal

is usually generated by the PLL circuit U4256BM.

Table 9. Gain of the FM IF Amplifier

Gain FM IF

Bit 91

Bit 90

Bit 89

19 dB

21 dB

23 dB

25 dB

27 dB

28 dB

29 dB

30 dB

Table 10. Temperature Coefficient Setting of FM IF Amplifier

Temperature Coefficient (TC) of the IF Amplifier

Bit 66

min (TK 1)

max (TK 2)

Table 11. 2nd Mixer Output Resistance in FM Mode

Bit 61

Bit 60

Output Resistance (Bit 54 = 0)

Output Resistance (Bit 54 = 1)

3.3 k

Ω

~100 k

Ω

0.63 k

Ω

0.78 k

Ω

0.47 k

Ω

0.55 k

Ω

0.29 k

Ω

0.32 k

Ω

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