LA7770 データシートの表示（PDF） - SANYO -> Panasonic

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LA7770

FSK Receiver for CATV Use

SANYO -> Panasonic 

LA7770

(3) IF Limiting Amplifier

The limiter amplifier employed is made up of DC feedback-provided 6-stage direct-coupled differential amplifiers.

Simplified, its circuit is represented in Fig. 4 below.

Fig. 4

Feedback gain (AV) will be AV=

A

1+Aβ

=

1

1 +β ≈

1

β

A

where feedback depth β = V2 =

1

V1 √1+ (ωCR)2

so that the decoupling capacitor C should be made sufficiently

large in capacitance within the operating frequency band to

achieve its low impedance.

(4) Quadrature Detector

The quadrature detector converts a frequency-modulated signal into a phase-modulated one by passing it through a

phase shifter, and then demodulates it by converting it again into voltage with its phase detector.

The quadrature detector block of the LA7770 is configured as shown in Fig. 5 below.

Fig. 5

Phase Shifter

The phase shifter is an important element of the quadrature detector, and it dictates the detection characteristics of

the latter.

The following phase-shifter-related parameters may be cited.

1. Demodulation output ........... Chiefly QL

2. Distortion Factor .................. Phase shifter linearity and symmetry of S curve

* While the phase shifting linearity may be enhanced with a single tuning circuit by lowering its QL and broaden-

ing its frequency band, its demodulation output will also be lowered in the process.

Fig. 6

No.2208–4/7

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