In the design of digital frequency meter, if only square wave signal needs to be measured, then there is no need for shaping circuit.
It is better to shape, because the square wave from the outside is easier to meet the requirements. But if there is no shaping, the rising edge and falling edge may not meet the requirements. If the upper body or falling is too slow, the logic judgment of the logic circuit will be wrong, resulting in the wrong counting of the counter. In this case, it is suggested to use Schmidt trigger for shaping.