| 摘要 |
PURPOSE:To improve a noise figure generated by high frequency noise, by supplying the output of a multistage amplifier of an emitter ground type driven by a power source by a constant-voltage circuit, to one base of an amplifying circuit consisting of two pairs of transistors of a double balance type mixing circuit, in a state of DC coupling. CONSTITUTION:A high frequency amplifying circuit block 1 is constituted of a two stage amplifying circuit of an emitter ground type consisting of transistors Q11, Q12 operated by obtaining a power source supplied from a high frequency amplifying power source circuit block 2, and the first IF signal is supplied from an input terminal Y. The output signal of the block 1 is supplied to a mixing circuit of a frequency converting circuit block 4 in a state that the DC potential of the block 1 remains held, through a low frequency eliminating circuit block 3. As for the bias to a transistor Q1 of the block 4, the collector voltage of the transistor Q12 of the block 1 is applied directly, and applied to the base of a transistor Q2 through a resistance R9 from the transistor Q1. Therefore, the high frequency amplification stage of the transistors Q1, Q<2> is separated from a high frequency component and a noise component leaked and applied through a power source line.
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