HEEPidermis: a versatile SoC for BioZ recording

Abstract

HEEPidermis is a versatile System-on-Chip (SoC) designed to overcome the limitations of bulky, fixed-purpose hardware currently used for biological impedance (BioZ) recording. This SoC integrates a complete measurement pipeline, including specialized analog-to-digital converters, arbitrary-signal current DACs, and a RISC-V CPU for on-chip feature extraction. Taped out on TSMC 65 nm LP, the HEEPidermis design enables closed-loop operation and improves long-term efficiency through event-based sub-sampling, with key components released as open-source assets.

Report

Key Highlights

• Integrated BioZ Solution: HEEPidermis is presented as a highly versatile System-on-Chip that consolidates all necessary blocks for tissue impedance measurement onto a single chip, eliminating the need for bulky external hardware.
• RISC-V Powered: The SoC utilizes a RISC-V CPU to facilitate on-chip feature extraction, which is essential for implementing sophisticated closed-loop monitoring operations.
• Efficiency Focus: An event-based sub-sampler is integrated to drastically improve storage and energy efficiency, supporting long-term, non-invasive health monitoring applications.
• Open Source Commitment: The digital back-end and behavioral models for the analog front-end are provided as open-source resources, enabling rapid system-level simulations and hardware repurposing by the research community.

Technical Details

• Function: Versatile SoC for Biological Impedance (BioZ) recording.
• Fabrication Process: Taped out on the TSMC 65 nm Low Power (LP) process node.
• Analog Output: Includes two 8-bit, arbitrary-signal Current DACs (Digital-to-Analog Converters) for stimulus generation.
• Analog Input: Incorporates two VCO-based ADCs (Voltage-Controlled Oscillator-based Analog-to-Digital Converters).
• Digital Core: Features an integrated RISC-V CPU.
• Data Handling: Uses an event-based sub-sampler to optimize data recording length and energy consumption.

Implications

• Advancing RISC-V in Edge Medical Devices: The successful integration of a RISC-V CPU into a specialized biomedical SoC validates the architecture's suitability for sophisticated, ultra-low-power, deeply embedded applications, such as wearables for health and emotional state monitoring.
• Democratization of BioZ Research: By providing an open-source digital back-end and analog models, the project significantly lowers the barrier to entry for researchers and startups developing custom BioZ sensing solutions.
• Enabling Closed-Loop Wearables: The combination of a powerful, efficient RISC-V core with integrated sensing hardware on a single die facilitates true real-time, closed-loop feedback systems, moving diagnostics beyond simple data collection to active intervention or adaptation.
• Miniaturization of Instrumentation: HEEPidermis represents a step towards fully integrated, highly compact instruments, replacing current bulky research equipment and accelerating the transition of BioZ technology into mass-market portable and wearable devices.