PURPOSE: To eliminate the fluctuation of the output terminal voltage at the control voltage switching time, i.e., the impulse noise by providing the switch circuit which selects only one of the output of the two input ampliying steps and applies the selected output to the output amplifier of the next step.
CONSTITUTION: The difference exists in that the switch circuit consisting of transistors Tr36∼39 plus constant voltage cource 27 is provided between the two output terminlas (collector terminals) of two input step emitter-earthed amplifiers 10 and 11 and the input terminal (base terminal) of output amplifier 12 in order to apply selectively only one of the output signals of amplifier 10 and 11 to the input terminal of amplifier 12. Even though the output of amplifiers 10 and 11 are switched via the above mentioned switch and with use of the control voltage of control terminal 4, the equal output DC voltage is obtained for output terminal 3 by setting resistance 23 and 24 plus 19 and 21 equal to each other and owing to the fact that the base terminals of Tr10 and 11 are biased by common voltage source 28 via resistance 15 and 16. So is for the amplifier by the control voltage at the side non-selected, thus eliminating the voltage fluctuation at the swithcing time.
TANAKA HIROMICHI
OOTA KANAME
