ATR4258 Datasheet, PDF (9/38 Pages) ATMEL Corporation – AM/FM RECEIVER IC

FM 1^st IF Amplifier
AM 1^st IF Amplifier
2^nd Mixer
ATR4258
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.
Table 9. Gain of the FM IF Amplifier
Gain FM IF
19 dB
21 dB
23 dB
25 dB
27 dB
28 dB
29 dB
30 dB
Bit 91
0
0
0
0
1
1
1
1
Bit 90
0
0
1
1
0
0
1
1
Bit 89
0
1
0
1
0
1
0
1
Table 10. Temperature Coefficient Setting of FM IF Amplifier
Temperature Coefficient (TC) of the IF Amplifier
TK_min (TK 1)
TK_max (TK 2)
Bit 66
0
1
In AM and WB mode, the gain of the 1^st IF amplifier is controlled by the IF-AGC to
extend the control range of the IF-AGC.
The 2^nd 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.
Table 11. 2^nd Mixer Output Resistance in FM Mode
Bit 61
0
0
1
1
Bit 60
0
1
0
1
Output Resistance (Bit 54 = 0)
3.3 kΩ
0.63 kΩ
0.47 kΩ
0.29 kΩ
Output Resistance (Bit 54 = 1)
~100 kΩ
0.78 kΩ
0.55 kΩ
0.32 kΩ
The LO frequency of the 2^nd mixer (10.25 MHz) has to be applied at pin 22. This signal
is usually generated by the PLL circuit U4256BM.
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