| 摘要 |
PURPOSE:To improve S/N and the resolution of an ultrasonic image by applying positive or negative DC voltage to the center tap of the initiary coil of a pulse transformer and to apply pulse voltage to both terminals of the primary coil by making and breaking the electronic switch of the same characteristics. CONSTITUTION:In the period of turning on and off the respective electronic switches Q1 and Q2 impressing input signals I1 and I2, the voltage of an input signal I3 is not impressed to the gate of an electronic switch Q3 in a switch circuit 5 to be in an off state, and after passing the period, the input signal I3 is impressed to the gate of the switch Q3 to make the switch Q3 into an on state. As the result of it, the secondary coil L2 of the pulse transformer T is short-circuited so as to make the signal source impedance looked at from an output terminal 4 have a low value close to the on resistance of the switch Q3. Thereby, concerning output pulse voltage Vo' from the terminal 4, a waveform does not collapse even at the lowest part of the pulse string of output voltage to make all the pulse strings keep the same waveform so that positive voltage and negative voltage become symmetrical. Consequently, they are the same in frequency spectrum of waveform. |
