On Automating Finger-Cap Array Synthesis with Optimal Parasitic Matching for Custom SAR ADC

Due to its excellent power efficiency, the successive-approximation-register (SAR) analog-to-digital converter (ADC) is an attractive design choice for low-power ADC implements. In analog layout design, the parasitics induced by interconnecting wires and elements affect the accuracy and performance of the device. Due to the requirement of low-power and high-speed, series of very small lateral metal-metal capacitor units are usually adopted as the architecture of capacitor array. Besides power consumption and area reduction, the parasitic capacitance would significantly affect the matching properties and settling time of capacitors. This work presents a framework to synthesize good-quality binary-weighted capacitors for custom SAR ADC. Also, this work proposes a parasitic-aware ILP-based weight-dynamic network routing algorithm to generate a layout considering parasitic capacitance and capacitance ratio mismatch simultaneously. The experimental result shows that the effective number of bits (ENOB) of the layout generated by our approach is comparable to or better than that of manual design and other automated works, closing the gap between pre-sim and post-sim results.