The figure is an experimental sine wave / square wave conversion circuit . When the input signal up to 3MHz , the output waveform is still a good rise and fall characteristics of the input signal in the range of between 0.2V to 10V . Output pulse amplitude is 6V, drive 50O load resistor , the pulse shape is not distorted . Working principle is very simple , no signal input , the circuit of all the transistors are in cut-off Zhuangtai , Dang enter by post- sinusoidal . signal positive half cycle Shi VT1 turn , Er Negative half-cycle signal to VT1 Jie Zhi . With the VT1 turn , the collector potential was decreased, so VT2 and VD2 conduction and VT2 of the collector to get a positive pulse , the positive pulse through the emitter VT3 output . VD2 for finishing top of the square wave . Similarly . When the input signal is negative and a half weeks, in the second half of the output circuit - a negative pulse .