KEY Drive strength is the max capacitance a cell can drive (.lib max_capacitance); fanout is the number of gates it drives.

Why Models Are Needed in CMOS Design

• They allow faster computation.
• They allow accurate computation.

KEY Models in CMOS design enable both faster and accurate computation.

Input Capacitance Across Drive Strengths

• Every standard cell is designed as two stages, with the first stage feeding the second.
• The first stage mainly implements the functionality of the cell.
• The second stage provides the driving capability of the cell.
• In higher drive-strength variants, only the second stage is strengthened.
• Because the first stage barely changes, the input capacitance stays nearly the same.

KEY Higher drive strength only strengthens the second stage, so the first-stage input capacitance stays similar.

D Flip-Flops Over JK Flip-Flops

A JK flip-flop has a race condition (in its toggle state), whereas the D flip-flop does not, so the D type is used.

KEY D flip-flops are chosen because JK flip-flops suffer from a race condition.

Why Multi-Voltage Designs Are Needed

• Lowering voltage reduces CMOS power, since dynamic power is (1/2)aC*V^2.
• Voltage: multiple voltage levels can be used as the requirement demands, which affects active power.
• Activity (toggle): clock gating reduces the switching activity.
• ON-OFF domains: powering domains off saves leakage power.