A 20-nW 0.25-V Inverter-Based Asynchronous Delta–Sigma Modulator in 130-nm Digital CMOS Process

Abstract

This paper presents a new inverter-based architecture that implements an asynchronous delta–sigma modulator. Different from the classical architecture, it features an input transconductor that promotes a differential and high input impedance that makes it easier to interface with sensors and other front ends. Furthermore, an inverter-based relaxation oscillator accomplishes the required hysteresis through a charge redistribution process, which exhibits lower time delay than hysteretic comparators, besides saving power from quiescent biasing. The circuit has been implemented in 130-nm CMOS digital process using halo-implanted transistors. In addition, transistors are biased in weak inversion and are implemented using distributed layout to reduce power consumption besides mitigating halo-implants undesired effects. Supplied with 0.25 V, the proposed architecture consumes 20 nW with just −55 dB of third harmonic distortion, making it suitable for wearable biomedical applications where energy consumption, low bandwidth, and moderate resolution are required.