An open-source adaptive event-based ADC for bio-signal acquisition in 130nm CMOS

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  • Speaker(s): Simon Dorrer
  • email: simon.dorrer@jku.at

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Abstract

Event-based ADCs offer significant advantages over Nyquist ADCs in applications where signals are sparse and exhibit substantial variations only within short time intervals, such as the QRS complex in an electrocardiogram (ECG). Unlike Nyquist ADCs, which sample data continuously at fixed rates and therefore often lead to unnecessary data and higher power consumption in time intervals of minimal signal variation, event-based ADCs only generate data when the signal exceeds a predefined voltage threshold. This makes them more energy-efficient, especially for battery-powered, wireless, and wearable devices, such as fitness trackers, medical sensors, and Internet of Things (IoT) devices. Adaptively adjusting these voltage thresholds further enhances efficiency.

This work first presents a PCB-level demonstrator to validate the feasibility of the event-based ADC concept. The demonstrator enables the development of a reconstruction framework for non-uniform data points in Matlab and Python and serves as a verification platform of the digital core on an FPGA. Subsequently, an event-based ADC is integrated utilizing open-source tools and IHP's 130nm CMOS technology. The analog circuit design uses Xschem, Ngspice, and Jupyter notebooks with gm/ID sizing scripts. Furthermore, the design consists of a digital core written in VHDL. Since some open-source tools prefer Verilog, the VHDL code is converted to Verilog using GHDL. Simulations are conducted with GTKWave, Surfer, or ModelSim, while register-transfer level (RTL) synthesis is performed using Yosys. The synthesized digital design is included in Xschem using Qflow scripts and Xspice, enabling analog-mixed signal (AMS) simulations. Finally, the digital layout is created with OpenROAD Flow scripts (ORFS).

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General information

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