The sine wave of 40Mhz can be shaped into a square wave, but it can't be simply shaped with 74HC 14 at lower frequency, because the speed of 74HC 14 is not high enough, and it is difficult to get an ideal waveform when used to shape the signal of 40MHz. The response delay time of 74HC 14 is about 10nS~20nS, and the rise and fall time is about 6nS, while the period of a complete waveform of a 40MHz signal is only 25nS. Only high-speed operational amplifiers can be used for shaping, such as OPA695, and the circuit form is slightly more complicated.