Negative current through R1 ramps up inverting integrator A1’s output until switch U1 resets it to zero. This topology is simple and works well, but it has the disadvantage of needing a separate ...

U3 is positive-edge-triggered and responds by driving U3pin6 low. This disconnects D2 from timing cap C2 and allows the current sink Q2 to ramp it down toward the switching threshold of U3pin 4 = -SET ...