Which state (switching or not switching) consumes more power? Which VT leaks more (HVT vs LVT)?

o   Switching State: The switching state consumes significantly more power in CMOS circuits. This is called dynamic power and has two main components:

o   Switching Power: Charging and discharging load capacitances (Psw​=αCVdd2​f, where α is activity factor, C is load capacitance, Vdd is supply voltage, f is frequency).

o   Short-Circuit Power: For a brief moment during switching, both PMOS and NMOS transistors can be partially ON, creating a direct path from VDD to VSS.

o   The non-switching (static) state consumes very little power, primarily due to leakage current (subthreshold leakage, gate leakage etc.), which becomes more significant at lower nodes.

o   VT Leakage: LVT (Low Threshold Voltage) cells leak more than HVT (High Threshold Voltage) cells.

o   Threshold Voltage (Vt): The minimum gate voltage required to turn a transistor ON.

o   LVT: Lower Vt means the transistor turns on "easier" (faster switching) but also allows more current to leak through even when it's supposed to be OFF (higher subthreshold leakage).

o   HVT: Higher Vt means the transistor requires more voltage to turn on (slower switching) but has significantly lower leakage current when OFF.

o   (ULVT/SLVT/ELVT are variations indicating Ultra/Super/Extremely Low Vt, with progressively higher leakage and speed).