A hybrid design automation tool for SAR ADCs in IoT

In this paper, a hybrid design automation tool for asynchronous successive approximation register analog-to-digital converters (SAR ADCs) in Internet-of-Things applications is presented. The circuit design-driven tool uses a top-down design approach and generates circuits from specification to layout automatically. A hybrid approach is introduced for different circuits of a SAR ADC: fully synthesized control logic; a script-based flow combining equations, library, and template-based design for the digital-to-analog converter; a lookup table approach combined with selective simulation-based fine tuning and template-based layout generation for the sample and hold; library-based comparator design and script-based layout generation. By balancing the automation and manual effort, the circuit design time is reduced from days down to minutes while still being able to maintain ADC performance. The proposed flow generated two ADC prototypes in 40-nm CMOS, an 8-bit 32 MS/s and a 12-bit 1 MS/s SAR ADC, and enabled excellent power efficiency. The two ADCs consume 187 and $16.7~\mu \text{W}$ at 1-V supply voltage, achieving 30.7 and 18.1 fJ/conversion-step, respectively.