Panasonic KX-B620 - Page 52

KX-B620 Series
KX-B520 Series
2-7 Video Signal Level Shift Circuit
1) Function
This analog circuit converts the video signal from the CCD board to the appropriate DC level and
gain signal for the IC 109.
2) Circuit Operation
“12V +12V
1C108
Fig. 26 Circuit Diagram
The digital conversion LS! (1C109 “MN86151”) inputs must be as follows:
Black Level = 0V
White Level = 5V
Because of the necessity of the conditions it is necessary to shift the DC level of the signal as shown
below.
2.5V—-4.5 V
2.5 V—-4.5 V ;
about 7 V GND
GND
0-200
mV
Fig. 27 Fig. 28
Black level of the signal from the CCD board is about 7V as shown above.
Its level is sampled and held by the analog switch 1C107 and condenser C111 at the timing of TG.
Signal level of TG1 and ¢TG is shown below.
Fig. 29 Timing Chart
This black level is subtracted from the original video signal, and still more the video signal is inverted.
This is accomplished by the differential amplifier 1C108.
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