BA1442A 데이터 시트보기 (PDF) - ROHM Semiconductor

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BA1442A

AM radio / FM IF stereo system IC

ROHM Semiconductor 

Audio ICs

FTechnical reference materials (unless otherwise noted, Ta = 25_C and VCC = 5V)

BA1442A

FCircuit operation

(1) The FM IF amplifier is a three-stage differential am-

plifier. The gain of this stage is approximately 60dB. The

bias for the first-stage amplifier is taken from the bypass

filter (pin 2). This improves the FM stability of the first-

stage amplifier by reducing noise. The input impedance

is set by a resistor on the chip (330Ω), and can be con-

nected to a ceramic filter.

(2) The FM detector circuit is comprised of a quadra-

ture detector. The IF amplified signal is input to the detec-

tor via a limiter amplifier with a gain of 13dB.

(3) The AM mixer is a double-balance type, and has

been designed for low local oscillator leakage. The mixer

bias current is added from Vreg via antenna coil. If you

lower the mixer conversion gain for mid- to high-strength

electric fields, AGC will operate, and for high-strength

electric fields, the input shunt AGC gives good strong-in-

put characteristics.

(4) The AM local oscillator circuit consists of a differen-

tial positive feedback loop. To improve the frequency sta-

bility, particularly in the SW band, the circuit is operated

with bias referenced to Vreg. To improve the startup char-

acteristics, a 100Ω resistor is inserted in series with the

tank circuit.

(5) The AM IF amplifier consists of two-stage differen-

tial amplifier. Both amplifiers use capacitors to block DC,

so bypass capacitors are not necessary. The first stage

amplifier has AGC. The gain of this stage is 47dB, and

the input impedance is 3kΩ.

(6) AM detector circuit

A built-in envelope detector that uses a minute current

serves as the AM detector. External components are not

required.

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