CXA3218N 데이터 시트보기 (PDF) - Sony Semiconductor

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CXA3218N

FM Demodulator for BS/CS

Sony Semiconductor 

CXA3218N

Description of Operation

The CXA3218N consists of the following four function blocks. First, the signal flow is explained briefly,

followed by the functions of each block.

(1) AGC circuit

(2) FM demodulation circuit

(3) Detection signal amplification circuit

(4) AFT circuit

The 2nd IF differential signal input to IF IN1 and IF IN2 (Pins 3 and 4) passes through the AGC circuit to fix the

signal level and is then input to the FM demodulation circuit.

The FM demodulated signal by the PLL demodulation circuit is then input to the DETAMP circuit and AFT

circuit.

The AFT circuit detects the frequency error of the 2nd IF signal by the detection output voltage value, and

outputs a command to the external frequency conversion circuits in order to correct the local frequency.

(1) AGC circuit

The 2nd IF differential signal is input to IF IN1 and IF IN2 (Pins 3 and 4) to fix the signal level by the AGC

circuit. A capacitor which determines the AGC loop time constant is connected to AGCLPF (Pin 25), and

the adjustment voltage at the AGC (2nd AGC) output setting level is applied to AGCCNT (Pin 26).

The 2nd AGC control voltage is output from IFAGC (Pin 30). The 1st AGC starting level adjustment

voltage for the 1st IF is applied to OPAINP (Pin 27). The MTRXAGC (Pin 1) output is input through a 0.1

µF capacitor.

The IFAGC (Pin 30) output is input to OPAINN (Pin 28) through a 10 kΩ resistor, and the 1st AGC control

voltage is output from OPAOUT (Pin 29). At this time, the IFAGC (Pin 30) output is used at the linear

portion against the input level. (See the Example of Representative Characteristics.)

The add voltage of the negative characteristics of the OPAOUT (Pin 29) output 1st AGC control voltage

and the IFAGC (Pin 30) output 2nd AGC control voltage is output from MTRXAGC (Pin 1).

2nd IF

signal input

34

2nd AGC circuit

AGCAMP

Cc

26

25

10k

30 28

0.1µF

27

29 1

1st AGC circuit

BOTH-SIDE

DETECTION

COMP

ic

Rc

(–) AMP

COMP

(–) AMP

To FM demodulator

—9—

(+) AMP

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