LA7555 데이터 시트보기 (PDF) - SANYO -> Panasonic

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LA7555

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

SANYO -> Panasonic 

LA7555

4. Lock detector

As shown in Fig.4-1, the lock detector is an APC time constant switching detection circuit which expands the APC

pull-in range. The detection circuit operates by the OR of the IF AGC voltage and the video signal. The weak field

is detected by the IF AGC voltage and the unlock state when detuned is detected from the video signal.

Fig.4-1

5. AGC detector

As shown in Fig.5-1, the AGC detector is equipped with a noise canceller function which prevents malfunction of

the AGC system. The AGC detection output (pin 13) is also used for video output, FM detection output, and as the

simultaneous mute (AV MUTE) pin.

Fig.5-1

6. RF AGC

As shown in Fig.6-1, the RF AGC controls the gain of the tuner’s RF amplifier. Measurement is made whether the

region is snow region (noise on the screen, poor S/N ratio) or a saturation region (contours can be clearly seen but

look bad due to video signal distortion), and the RF AGC delay point is set as shown in Fig6-2. Pin 10 is also used

for video output, FM detection output, and as the simultaneous mute (AV MUTE) pin.

Fig.6-1

Fig.6-2

No.2927–6/11

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