dynamic power in CMOS

[srikanth1986]

Why is energy per transition in an inverter Cload*Vdd^2 and not half of it as per the formula?

 

[apallix]

Total energy dissipated per charge+discharge cycle of a cap Cload is Cload*Vdd^2.

In the charge cycle, the PMOS dissipates 1/2*Cload*Vdd^2 energy and another 1/2*Cload*Vdd^2 energy is transferred to the cap Cload that stores it.

In the following discharge cycle, the NMOS dissipates the 1/2*Cload*Vdd^2 energy that was stored in the cap.

Total energy dissipated is Cload*Vdd*2.