| 摘要 |
PURPOSE:To prevent the malfunction of a synchronous detecting circuit by providing an adder, which adds detection output voltages of synchronous detecting circuits, and a means which controls the gain of an amplifier so as to keep the output voltage of this adder constant. CONSTITUTION:Output voltages Va-Vd of detectors 9a-9d are added by an adder 14. The sum of said output voltages Va-Vd is compared with a reference voltage Vr by an error signal amplifier 1, and a control voltage proportional to the difference between said sum and the reference voltage Vr. The gain is controlled in a gain control amplifier 3, and the output voltage goes to Va+Vb+ Vc+Vd=Vr. Since the gain is automatically controlled so as to keep the sum of the detection output voltages of synchronous detecting circuits constant, so that the malfunction of synchronous detection is prevented. |
