I want to generate a pulse that have frequency 40khz and amplitude 20VPP to MA40s4s ultrasonic sensor operate. I use raspberry to generate pulse 40khz-5Vpp then using a IC CD4049BE to boost it into 20vpp as in the below figure. I have encountered the problems is that when i not insert sensor into circuit is waveform is very good but when i insert sensor, waveform is noised as in figure.Please give me how to resolve this problem. enter image description here enter image description here

  • \$\begingroup\$ Your 'scope photo shows only one side of the driver (either TP3 or TP4). The other side should appear similar, with 180 degree phase inversion. If so, I see no problem. You might want to increase C8 (more than 0.1uf) - it should be placed close to U3 power pins. \$\endgroup\$ – glen_geek Nov 10 '16 at 16:39

Capacitance of MA40S4S (about 2.55 nF) affects output of the power stage.

Consider using an IC with higher output current.

Or you can try a burst generator (mosfet + inductor) driven by the PWN signal. Example you can find on page 9 of AN4841: 12ZVL LIN Enabled Ultrasonic Distance Measurement.


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