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LA7555

IF Signal Processing (VIF+SIF) Circuit for TV / VCR Use

SANYO -> Panasonic 

LA7555

2. Video detector

As shown in Fig.2-1, the video detector is a PLL-type. AM detection (video detection) is by phase shifting the IF

signal and VCO output signal 180° and multiplying the input signal. It offers excellent buzz and beat characteris-

tics as detection is by multiplication by a clean signal. Also, excellent detection characteristics are obtained in the

same manner for the overmodulation signal.

Fig.2-1

3. Video amplifier B/W noise canceller

As shown in Fig.3-1, the video amplifier amplifies the detection output voltage over a wide band to the desired

voltage (=2.2Vp-p). The amplified video signal passes through the B/W noise canceller and is output to pin 21.

White : The noise canceller operates as shown in Fig.3-3 as the input of noise exceeding the white level of the

video signal as shown in Fig.3-2 will cause noticeable noise on the screen.

Black : The noise canceller operates as shown in Fig.3-3 as the input of noise exceeding the sync signal tip as

shown in Fig.3-2 will prevent proper operation of the next-stage sync separation circuit.

Fig.3-1

Fig.3-2

Fig.3-3

No.2927–5/11

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