EXCESSIVE INPUT PROTECTION CIRCUIT, AND EXCESSIVE INPUT PROTECTION METHOD

摘要

PROBLEM TO BE SOLVED: To protect a circuit without deteriorating a high frequency characteristic even when a protection circuit is damaged by an excessive input in a monolithic microwave integrated circuit for receiving high frequency signals.SOLUTION: An excessive input protection circuit 11 has plural stages of anti-parallel diodes 21a and 21b, and each stage of FETs 22a and 22b. The anti-parallel diodes 21a and 21b actuate as excessive input protection elements. The FETs 22a and 22b actuate as switching elements for connecting or disconnecting each stage of the anti-parallel diodes 21a and 21b between a high frequency transmission line 13 and a ground. When the anti-parallel diode 21a is damaged, the FET 22a has a high impedance and the FET 22b has a low impedance. Instead of a first stage of the anti-parallel diode 21a, the next stage of the anti-parallel diode 21b functions as an excessive input protection element.