When M0 an M1 turn on, the threshold voltage in Fig(a),(b) is low. When M0 and M1 turn off, the threshold voltage is high. But in Fig(b). I want to know how to find out the rise time and fall time in Fig(a) and (b). Which one is larger? Assuming there are parasite capacitor in MOS. I couldn't calculate out the rise time and fall time.