HEEPidermis: a versatile SoC for BioZ recording

2025-09-03

AI Summary

Existing bioimpedance measurement systems rely on bulky, inflexible hardware, limiting their applicability in wearable and long-term physiological monitoring. To address this, we present a portable, multifunctional System-on-Chip (SoC) for noninvasive monitoring of health and emotional states. Fabricated in TSMC 65-nm low-power CMOS technology, the SoC integrates a current-mode DAC, a voltage-controlled oscillator–based ADC (VCO-ADC), and a RISC-V processor. It introduces, for the first time, an event-driven sub-sampling mechanism that significantly improves energy efficiency and memory utilization. The chip supports on-chip feature extraction and closed-loop operation, and is compatible with open-source digital back-end tools and analog behavioral models. Post-fabrication validation confirms its capability for efficient impedance acquisition, real-time signal processing, and rapid system reconfiguration. This work delivers a highly integrated, ultra-low-power, and scalable hardware platform enabling personalized, continuous physiological monitoring.

Technology Category

• Machine Learning: Hardware-aware ML
• Cognitive Modeling & Cognitive Systems: Neural Spike Coding
• Application Domains: Internet of Things, Sensor Networks & Smart Cities

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Security and Privacy: Large-scale security measurements

Abstract

Biological impedance (BioZ) is an information-packed modality that allows for non-invasive monitoring of health and emotional state. Currently, most research involving tissue impedance is based on bulky or fixed-purpose hardware, which limits the scope of research and the possibilities of experiments. In this work, we present HEEPidermis: a System-on-Chip (SoC) which integrates all the blocks needed for tissue impedance measurement, including two 8-bit, arbitrary-signal current DACs, two VCO-based ADCs, and a RISC-V CPU to enable on-chip feature extraction for closed-loop operation. An event-based sub-sampler improves storage and energy efficiency for long-term recording. In addition to the versatile SoC, the digital back-end and behavioral models of the analog front-end are open-source, allowing fast system-level simulations or repurposing. The SoC was taped out on TSMC 65 nm LP process.

Problem

• Develops a versatile SoC for biological impedance recording
• Addresses limitations of bulky fixed-purpose BioZ hardware
• Enables on-chip feature extraction for closed-loop operation

Innovation

• SoC integrates tissue impedance measurement blocks
• Event-based sub-sampler enhances energy efficiency
• Open-source digital backend enables system simulations