| 摘要 |
PROBLEM TO BE SOLVED: To provide an impedance matching circuit that matches impedance inside and outside a communication apparatus by connecting a resistance parallelly with a transformer and also between the inverted input terminal and an output terminal of an operational amplifier on the primary side of the transformer. SOLUTION: This impedance matching circuit 1 is provided with a resistance R11 for matching parallelly with a transformer T10 and also between the inverted input terminal side and an output terminal of the an operational amplifier IC 10 in the primary side of the transformer T10. Then, an output signal from the amplifier IC 10 passes through the resistance R11 or the transformer T10 and is used as a negative feedback signal of the amplifier IC 10, an output signal of a secondary side of the transformer T10 which is generated by the mutual induction of the transformer T10 is outputted from output terminals 011 and 012 in the communication apparatus to the outside of the communication apparatus to drive the load resistance R10 of a line of a signal output destination. Thus, impedance seen from the secondary side of the transformer T10 becomes R11 and impedance is matched inside and outside the communication apparatus.
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