| 摘要 |
PURPOSE:To eliminate harmonics of the lower limit frequency by extracting a signal at the lower limit frequency of an amplifier and using the signal to switch a pin diode element. CONSTITUTION:When a signal at the lower limit frequency band of the amplifier is inputted, a series resonance circuit comprising an inductor element 32 and a capacitor 33 is resonated. Then a part of the signal appears at the anode side of a detection diode 35, the signal is detected by the detection diode 35 and a DC signal is obtained, which is inputted to an arithmetic unit 39 via a resistor 38. When an output voltage of an operational amplifier 39 reaches a prescribed value or over, a switching transistor (TR) 44 is turned on and a switching TR 49 is turned off, a pin diode 27 is turned on and a pin diode 55 is turned off. a parallel resonance circuit comprising a capacitor 25 and an inductor element 26 is the pass band at the lower limit frequency and has an infinite impedance at a frequency twice the lower limit frequency.
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