Square Wave Generator
The utility of a square wave generator (clock) is overall accepted. Bellow, we present a schematic we use to check the behavior of an experiment at a large frequency spectrum:
We use the classic astable setup with: LM555. The R3 potentiometer (1Mo) helps to modify the “duty cycle”, and the capacitor C1 sets (with R3) the frequency. The value of C1 can be adjusted between :10pF and 10Uf , so we can get a large frequency spectrum.
The output of U1 can be distorted, especially at high frequencies. So in order to improve the signal shape, we will regenerate it through a Schmitd trigger type : 7414
(ex: DM74LS14N). On the output we use an emitter follower (Q1) to get a lower output impedance.