Ask the expert how the 20kHz waveform in the picture can make its amplitude smaller, even 0V, and how to shorten the next rising time. ask sb. to do sth.
Look at the waveform below, it should be about 0 to 3 V. The peak value of 20khz voltage is about 1V, which can be eliminated by 74HC 14 Schmitt inverter. Under 5V power supply, the forward and reverse threshold of 74HC 14 is about 1.7V, so when the signal is higher than this voltage, U 1A outputs a low level. U 1A outputs a high level when the signal is lower than the negative inversion threshold of about 1V, and the peak voltage is lower than the inversion threshold, so it always outputs a high level during this period, and the slowly rising waveform will also be shaped into a steep rising edge, and the inverted signal will be reduced to a pulse in the same direction as the input signal through u1b.