An Active Low Input Capacitance Bond Pad for CMOS Sensor Interface Circuits

A shielded active pad is suggested with its shield driven by a voltage follower whose input is connected to the signal applied to the pad. A special pad and a related circuit are designed and realized as a layout using a 6 metal 180 nm standard CMOS process. Aiming for low to medium frequency operation, post-layout simulations predict an effective input capacitance below 2.5 fF in the frequency range of 0 - 100 kHz.