| 摘要 |
PURPOSE:To obtain an inexpensive ultrasonic detection apparatus, by changing over the impedance of the synchronous circuit of an amplifier corresponding to the input level of the amplifier. CONSTITUTION:Low voltage diodes 22, 33 are inserted in a synchronous circuit 31 in parallel in reverse connection. When the resonance voltage of the synchronous circuit 31 exceeds the Zener voltages of the low voltage diodes 32, 33, the diodes 32, 33 are brought to a continuity state and the impedance of the synchronous circuit 31 is abruptly reduced to reduce the size of resonance and, therefore, the amplification degree of an amplifier is lowered to a large extent. On the other hand, when the resonance voltage of the synchronous circuit 31 is equal to or less than the voltages of the diodes 32, 33, the synchronous circuit 31 is brought to such a state that almost infinite resistance are inserted in parallel and the amplification degree of the amplifier becomes large. As a result, the reduction of a dead zone is simply attained and an inexpensive ultrasonic detection apparatus can be obtained. |
