A 102.2-dB, 181.1-dB FoM Extended Counting Analog-to-Digital Converter with Capacitor Scaling

Sensor interfaces demand ever-increasing energy efficiency from analog-to-digital converters (ADCs). For sensors requiring a wide dynamic range (DR) (>12 bit), the incremental ADC (IADC) is becoming a popular choice. In this article, the design of an energy-efficient IADC with a 16-bit signal-to-noise and distortion ratio (SNDR) and 17-bit DR is described. The IADC implements a novel capacitor scaling technique, which reduces power consumption in the critical first operational transconductance amplifier (OTA) by up to 37%. The new technique can be combined with the extended counting (EC) scheme utilizing an in-loop 4-bit asynchronous successive approximation register (SAR) (ASAR) ADC. Using a three-phase operation, this IADC architecture further reduces the power while enabling wider signal bandwidth with a much lower oversampling ratio (OSR). Silicon measurements in a 0.18-μm CMOS process show the IADC achieved a DR of 102.2 dB, within a bandwidth of 2.04 kHz, with power consumption of about 25μW, leading to a state-of-the-art Schreier figure-of-merit (FoM) of 181.1 dB.