Switched CMOS current source compared to enhanced Howland circuit for bio-impedance applications

Area of Science:

• Biomedical Engineering
• Electrical Engineering
• Wearable Technology

Background:

• Bio-impedance Spectroscopy (BIS) is crucial for disease diagnosis and tissue analysis.
• Wearable healthcare devices require miniaturized, low-power CMOS integrated circuits for bio-impedance analysis.
• Existing current sources like the Enhanced Howland Current Source (EHCS) have limitations with broadband signals and power efficiency.

Purpose of the Study:

• To evaluate the performance of a novel Switching CMOS Current Source (SCMOSCS) against the EHCS for BIS applications.
• To assess the suitability of SCMOSCS for ultra-low power, high-performance wearable bio-impedance analysis.
• To compare current source capabilities using a Cole-skin model under various simulation conditions.

Main Methods:

• SPICE simulations were employed, including DC and AC sweeps and transient analysis.
• The performance of SCMOSCS was evaluated against EHCS using a Cole-skin model as a load.
• Key performance metrics such as output impedance, voltage swing, current consumption, and load capacity were measured.

Main Results:

• SCMOSCS achieved an output impedance exceeding 20 MΩ, a ±2.5 V output voltage swing from a 3.3 V supply, and supported a 10 kΩ load.
• SCMOSCS demonstrated significantly lower current consumption (275 μA) compared to EHCS (4.9 mA).
• EHCS exhibited a limited +1.5 V output voltage swing and a 3 kΩ load capacity.

Conclusions:

• SCMOSCS offers a more compatible and high-performance solution for bio-impedance analysis in wearable devices, especially with broadband signals like DIBS.
• The SCMOSCS design provides superior output voltage swing, load capacity, and power efficiency over EHCS.
• This advancement supports the development of next-generation, battery-powered wearable healthcare devices for enhanced diagnostics.