| 摘要 |
PURPOSE:To make an output level constant and also to prevent malfunction due to noise by providing a positive feedback circuit to an adder circuit for detecting a picture of an FM carrier reproducing signal so as to provide Schmitt function. CONSTITUTION:An adder circuit for two signals Vi1, Vi2 detecting the defect of picture from the FM carrier reproducing signal is constituted as a differential amplifier circuit constitution comprising of the 1st transistors (TRs) 3, 4 and the 2nd TR5 and the Schmitt function (hysteresis characteristic) is given by applying positive feedback to the base of the 2nd TR5 via an emitter follower comprising a TR31. The width of Schmitt function is set freely depending on values of a resistor 32 and a constant current source 33, and the operation response is quickened by output feedback and an output high level is made uniform and malfunction due to noise is prevented in the adder circuit.
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