| 摘要 |
PURPOSE:To preform DC restoration accurately without spoiling linearity by detecting the difference in the peak level of an output signal with a Zener diode, and smoothing and feeding it back to a preamplifier. CONSTITUTION:An input signal is supplied to the base of a transistor TR4 through a capacitor C2 to obtain an impedance-converted signal from the emitter of the TR5. At this time, a light and a dark signal hae different in peak level. For the purpose, a synchronizing signal part is extracted by the Zener diode having a Zener voltage a little bit lower than the peak level voltage and smoothed by a capacitor C3 into a direct current, which is fed back to the base of the TR4 through a resistance R14. Consequently, the peak levels of output signals of the dark and light signals are constant and the direct current is reproduced. The DC voltage is fed back, so the linearity of the signal is not spoiled.
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