| 摘要 |
A ladder LPF includes a first capacitor formed of a transistor in which two terminals out of three are diode-connected, and a second capacitor formed by connecting a pn junction capacitor and an insulating capacitor in parallel. In the second capacitor, the pn junction capacitor formed in a semiconductor layer and the insulating capacitor formed in a surface of the semiconductor layer are connected to each other in parallel so as to almost overlap each other. Accordingly, the area in the LPF occupied by the second capacitor can be prevented from increasing even when its capacitance value is increased. Moreover, having the snap-back characteristics, the first capacitor can protect the second capacitor having the insulating capacitor from ESD. As a result, what can be obtained is a compact noise filter having high RFI removal characteristics and accomplishing high resistance to ESD.
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