LM324 op amp makes a step wave generator

Figure 1 is a practical circuit of a step wave generator composed of current-type operational amplifiers. Operational amplifier A1 and peripheral components constitute a rectangular wave generating circuit, which outputs a pulse train. Operational amplifier A2 and its peripheral components are an integration-holding circuit. Its integrating capacitor integrates the input pulse and maintains the step of the input pulse. What is obtained at the output end is the accumulation of each step, that is, the step wave. Operational amplifier A3 is a voltage comparator. When the step wave voltage rises to about 80% of the power supply voltage, A3 flips. Operational amplifier A4 and its peripheral components are monostable circuits. The flip of A3 causes it to output a pulse (about 100uFs), which is used as a reset pulse to reset A2, thereby completing a step cycle. The circuit diagram is as follows: