I need to design a circuit that has this function. There is an input signal whether ON or OFF. I need this: Once the input signal is ON first, my output must be ON also and after that it has to stay ON no matter what!

Like the timing diagram below.

S1 is the input signal and S2 is supposed to be the output,

[![timing](https://i.stack.imgur.com/7XIlR.jpg)](https://i.stack.imgur.com/7XIlR.jpg)

when the input signal is ON for the first time, I need to output ON and after this, input signal may change but my output should stay ON! How can I implement this in transistor level?