BA1442A 查看數據表（PDF） - ROHM Semiconductor

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BA1442A

AM radio / FM IF stereo system IC

ROHM Semiconductor 

Audio ICs

BA1442A

(7) AM AGC circuit

AGC is applied to the input shunt, mixer , and IF circuits.

The AGC reduces the mixer and IF circuit current, and

according the DC level of the detector output, reduces

the gain to control the output at a fixed level. In addition,

an input shunt is provided to prevent distortion caused by

strong input signals. The AGC pin is also used as the

MPX PLL filter pin. For this reason, when there is no in-

put, the AGC voltage becomes Vreg (pin 19), and when

there is a strong input signal, it is about Vreg - 0.2V.

(8) AM / FM detector circuits

There is one pin for both detector outputs (pin 6), and the

AM / FM switching is done internally. The output imped-

ance is 5kΩ, and the DC output is 1.3V.

(9) The FM MPX circuit uses a PLL to recover the ste-

reo. For FM, the input from pin 7 is switched by the de-

coder and output on pin 11 (L channel) and pin 12 (R

channel). In the case of AM, the input is from pin 8, and

this is output through to pins 11 and 12. The audio fidelity

is improved by the low-pass filter comprised of the capac-

itor connected between pins 6 and 8 and the input imped-

ance of pin 8 (20kΩ). The input / output gain for both AM

and FM is about 6dB. The VCO has been laser trimmed

on the chip to set its time constant. External components

and re-adjustment are not required.

FApplication example

343

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