| 摘要 |
PROBLEM TO BE SOLVED: To reduce the number of circuit elements without losing the balance of a balanced circuit by connecting a first resistance element between signal lines at the time when the level of a signal inputted to a signal line exceeds a prescribed value. SOLUTION: A pair of signal lines 4 and 5 are connected to two input ends of a balanced amplifier 1 through DC blocking capacitors 2 and 3 respectively, The collector of an NPN transistor TR 6 is connected to one signal line 4, and a first resistance element 7 for signal attenuation is connected between its emitter and the other signal line 5. In this circuit, a voltage is not applied to the other end T of a third resistance element 9 when the level of the signal inputted between signal lines 4 and 5 is equal to or lower than the prescribed value, and it is applied when the signal level exceeds the prescribed value. Then, a base current flows between the base and the emitter of the TR 6 to set the circuit between the collector and the emitter to the conductive state, and the first resistance element 7 is inserted between signal lines 4 and 5 with respect to high frequency.
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