Any mismatch in capacitance between the NMOS and PMOS transistors results in a charge injected into the drain or source during the falling or rising edge of the gate signal. The amount of charge injected into the source or drain of the device is known as charge injection, and is denoted by the symbol Q_C. Figure 7-8 shows the setup used to measure charge injection from source (Sx) to drain (D).

Figure 7-8 Charge-Injection Measurement Setup