LA7555 View Datasheet(PDF) - SANYO -> Panasonic
Part Name
Description
Manufacturer
LA7555 Datasheet PDF : 11 Pages
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LA7555
7. AFT
As shown in Fig.7-1, the AFT is a balanced-type using a quadrature detection circuit. The input signal is shifted
90° by the internal capacitor and external phase shifter, and quadrature-detected. Pin 14 is also used as the AFT
Defeat pin. Fig.7-1
Fig.7-1
C2 forms a sound trap for preventing malfunction of the AFT.
8. SIF limiting amplifier
As shown in Fig.8-1, the SIF limiting amplifier is an unbalanced limiting amplifier consisting of four stages
derectly connected. There is negative feedback within the IC to balance the differential amplifier.
Fig.8-1
9. Quadrature detection
SIF quadrature detection is by the single pin detector with internal phase shift capacitor, shown in Fig.9-1. FM
detection is by shifting the SIF signal 90° and multiplying it. The characteristics of the phase shifting circuit are as
follows :
1. Demodulation output ..... mainly QL
2. Distortion ... linearity of phase shifting circuit, symmetry of S curve.
The linearity of the phase shifting circuit can be improved by lowering QL and increasing the band with a single-
tuned circuit, but the FM detection output will drop.
Pin 2 is also used as the SIF mute pin.
Fig.9-1
10. Electronic volume control
As shown in Fig.10-1, this is an electronic volume control, having a control pin with high input impedance. The
attenuation curve is a logarithmic curve. The external audio input impedance is approximately 30kΩ.
No.2927–7/11
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