Circuit with high-density capacitors using bootstrapped non-metal layer

• Main Author: McLeod, Scott C
• Format: Patent
• Language: English
• Published: 30.10.2012

A switched-capacitor circuit on a semiconductor device may include accurately matched, high-density metal-to-metal capacitors, using top-plate-to-bottom-plate fringe-capacitance for obtaining the desired capacitance values. A polysilicon plate may be inserted below the bottom metal layer, and bootstrapped to the top plate of each capacitor in order to minimize and/or eliminate the parasitic top-plate-to-substrate capacitance. This may free up the bottom metal layer to be used in forming additional fringe-capacitance, thereby increasing capacitance density. By forming each capacitance solely based on fringe-capacitance from the top plate to the bottom plate, no parallel-plate-capacitance is used, which may reduce capacitor mismatch. Parasitic bottom plate capacitance to the substrate may also be eliminated, with only a small capacitance to the bootstrapped polysilicon plate remaining. The capacitors may be bootstrapped by coupling the top plate of each capacitor to a respective one of the differential inputs of an amplifier comprised in the switched-capacitor circuit.