In fact, the oscillations are all sine waves. It may be a square wave after shaping. You can make an oscillation circuit with a 5MHZ crystal oscillator. If you don't understand many things on the Internet, then the waveform output terminal is connected to the input of the comparator, and the other input of the comparator is connected to the reference voltage. It is a 5MHZ square wave after shaping. Duty cycle is to adjust the size of reference voltage.