ATR4255P-ILQY Datasheet ATR4255P-ILQY, ATR4255P-ILSY | P7-P9

4883B–AUDR–01/06

ATR4255P

3.5 AM RF-AGC

The AM RF-AGC controls the current into the AM pin diodes (pin 7) and the source drain voltage

of the MOSFET in the AM preamplifier stage (pin 6) to limit the level at the AM mixer inputs

(pin 3, pin 41). This threshold level can be set by bits 62 and 63 (Table 3-4). If the level at the

AM mixer input exceeds the selected threshold, the current into the AM pin diodes is increased.

If this step is not sufficient, the source drain voltage of the MOSFET is decreased. The time con-

stant of the AGC control loop can be adjusted by changing the value of the capacitor at pin 8.

3.6 FM 1

Mixer

In the 1

FM mixer stage, the FM reception frequency is down converted to the 1

IF frequency.

The VCO frequency is used as LO frequency for the mixer.

3.7 AM 1

Mixer

The AM 1

mixer is used for up-conversion of the AM reception frequency to the 1

IF fre-

quency. Therefore, an AM prescaler is implemented to generate the necessary LO frequency

from the VCO frequency. The divide factor of the AM prescaler can be selected as shown in

Table 3-5.

Table 3-3. FM-AGC Threshold

FM-AGC Threshold Bit 65 Bit 64

104 dBµV 0 0

101 dBµV 0 1

98 dBµV 1 0

92 dBµV 1 1

Table 3-4. AM-AGC Threshold

AM-AGC Threshold Bit 63 Bit 62

99 dBµV 0 0

102 dBµV 0 1

104 dBµV 1 0

105 dBµV 1 1

Table 3-5. Divide Factor of the AM Prescaler

Divider AM Prescaler Bit 93 Bit 92 Bit 84 Bit 83 Bit 82 Bit 81

Divide by 10 1 0 x 0 0 0

Divide by 6 1 0 x 0 0 1

Divide by 7 1 0 x 0 1 0

Divide by 8 1 0 x 1 0 0

Divide by 4 1 0 x 1 0 1

4883B–AUDR–01/06

ATR4255P

3.8 FM 1

IF Amplifier

A programmable gain amplifier is used in FM and WB mode between pin 38 and pin 30 to com-

pensate the loss in the external ceramic band filters. The gain of this amplifier is adjusted by

bits 89 to 91 (Table 3-6). The input and the output resistance is 330Ω, and fits to external

ceramic filters.

Two different temperature coefficients (TC) of the FM IF amplifier can be selected by setting

bit 66 (

Table 3-7).

3.9 AM 1

IF Amplifier

In AM mode, the gain of the 1

IF amplifier is controlled by the IF-AGC to extend the control

range of the IF-AGC.

3.10 2

Mixer

The 2

mixer is used in AM, FM and WB mode. The mixer input has 330Ω input resistance 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 band-

width of the tank at the mixer output. The output resistance can be selected by bits 60 and 61

(

Table 3-8).

The LO frequency of the 2

mixer (10.25 MHz) has to be applied at pin 22. This signal is usually

generated by the PLL circuit ATR4256.

Table 3-6. Gain of the FM IF Amplifier

Gain FM IF Bit 91 Bit 90 Bit 89

20 dB 0 0 0

22 dB 0 0 1

24 dB 0 1 0

26 dB 0 1 1

28 dB 1 0 0

29 dB 1 0 1

30 dB 1 1 0

31 dB 1 1 1

Table 3-7. Temperature Coefficient Setting of FM IF Amplifier

Temperature Coefficient (TC) of the IF Amplifier Bit 66

min

max

Table 3-8. 2

Mixer Output Resistance in FM Mode

Bit 61 Bit 60 Output Resistance (Bit 54 = 0) Output Resistance (Bit 54 = 1)

0 0 3.3 k

Ω ~100 kΩ

0 1 0.63 kΩ 0.78 kΩ

1 0 0.47 kΩ 0.55 kΩ

1 1 0.29 kΩ 0.32 kΩ

4883B–AUDR–01/06

ATR4255P

3.11 2

IF Amplifier

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

to the 2

mixer 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

mixer 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

mixer tank and pin 28 in FM mode by

setting bit 54 to “1”.

3.12 IF-AGC

The IF-AGC controls the level of the 2

IF signal that is passed to the AM demodulator input or

the integrated FM bandfilter, and to the 2

IF 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.

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.

Table 3-9. FM Bandwidth (BW) Mixer 2

Bit 61 Bit 60 FM BW Mixer 2

0 0 150 kHz

0 1 200 kHz

1 0 250 kHz

1 1 450 kHz

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

Table 3-10. 2

IF Filter in FM Mode

IF Filter Bit 54

Internal filter 0

External and internal filter 1

Table 3-11. IF-AGC Time Constant

Mode Bit 92 Bit 88 IF AGC Time Constant

FM/WB 1 x IFAGCL (fast)

AM reception 0 0 IFAGCH (slow)

AM search 0 1 IFAGCL (fast)

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27 P28-P30 P31-P33 P34-P34

ATR4255P-ILQY

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RF Receiver COM.RADIO - AM/FM RECEIVER

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