Minimum energy point: definition

Beginner

The power-supply level where a circuit does each job with the least energy. Go lower and the chip gets so slow that leaking wastes more than you save.

Novice

The supply voltage that minimizes energy per operation. Below it, each operation takes so long that the leakage energy collected during it outweighs the switching energy saved.

Expert

The minimum of $E(V) = \alpha C V^2 + V I_{\mathrm{leak}} t_{\mathrm{op}}(V)$ . Switching energy falls as $V^2$ , but $t_{\mathrm{op}}$ rises exponentially below $V_{\mathrm{T}}$ , so the minimum usually sits near or just below threshold. It moves up when activity is low or leakage is high, and down when activity is high.