The design of capacitor structures have great impact on capacitance density, parasitic capacitance, routability, and matching quality of capacitor network in a SAR ADC, which may affect power, performance, and area of the whole data converter. Most of the recent studies focused on common-centroid placement and routing optimization of the capacitor network. Only few of them investigated the structures of highly integrated capacitors. In this paper, a novel mortise-tenon metal-oxide-metal capacitor structure is proposed, which has the advantages of high capacitance density and small parasitic capacitance. Based on the proposed structure, an integer-linear-programming based capacitor sizing and routing parasitic matching method is further introduced. Experimental results show that the proposed structure and method can achieve the best capacitance density and matching quality of the capacitor network in a SAR ADC.

Capacitor sizing is a crucial step when designing charge-scaling digital-to-analog converters (DACs). Larger capacitor size can achieve better circuit accuracy and performance due to less impact from process gradient, parasitic mismatch, and local variation. However, it also results in larger chip area and higher power consumption. The size of binary-weighted capacitors in charge-scaling DACs is highly sensitive to the routing parasitics. Unmatched routing parasitics among binary-weighted capacitors will lead to large capacitor size for satisfying circuit accuracy and performance. Previous work focuses on the study of generating high-quality common-centroid placement of unit capacitor arrays while ignoring routing parasitics. None of them address the sizing of binary-weighed capacitors. This paper presents the first problem formulation in the literature which simultaneously considers capacitor sizing and parasitic matching during common-centroid capacitor layout generation such that the power consumption is minimized while the circuit accuracy/performance is also satisfied. Experimental results show that the proposed approach can achieve very significant chip area and power reductions compared with the state-of-the-art approaches.

As technology advances, smaller feature size enables layout precision in the lateral direction. In contrast to traditional metal-insulator-metal capacitors, metal-oxide-metal (MOM) capacitors are generally of higher density and consume less area, because they adopt a 3-D topology over several metal layers to use lateral field capacitance. To achieve little area consumption, MOM capacitors require new layout methods with routing even before placement. Since the routing wires are of comparable size to unit capacitors in MOM design, routing-induced parasitic capacitance must also be considered. To obtain a higher yield, common-centroid layout style and high dispersion of cells are desired. This paper introduces a new vertical bars structure for binary weighted MOM capacitor arrays and presents a new method to generate common-centroid regular-structured layouts with mismatch reduction and routing-parasitic-matching consideration. Experimental results show that the presented approach generates high-density, low-powered, and highly accurate ratioed capacitors.