1, which is an emitter-coupled monostable circuit, also called Schmidt trigger. It can convert the input analog signal into a square wave and output it, so it can be used as an A/D converter and a shaping circuit.

2. Under normal circumstances, T 1 is cut off and T2 is saturated. When the input terminal voltage is higher than a certain value, T 1 becomes saturated and T2 is turned off.