Automatic Drift Cancellation of Implanted Bladder Pressure Sensor.

Area of Science:

• Biomedical Engineering
• Sensor Technology
• Instrumentation Systems

Background:

• Implanted pressure sensors experience long-term offset drift from environmental and patient-specific factors.
• Traditional wide dynamic range instrumentation increases power consumption in medical devices.
• AC-coupling methods are insufficient for monitoring static pressures, limiting sensor applications.

Purpose of the Study:

• To present a mixed-signal offset cancellation loop for maximizing the AC dynamic range of instrumentation circuitry.
• To develop a digital implementation for power-gated pressure sensors with controllable time constants.
• To enable accurate static pressure monitoring in implanted medical devices.

Main Methods:

• A digital offset cancellation loop was designed and implemented.
• Pressure offset is determined via digital integration.
• A bipolar current-steering digital-to-analog converter (IDAC) injects an offset-cancelling current into a piezoresistive MEMS pressure sensor.

Main Results:

• A dynamic range increase of 2.9 bits was achieved using the proposed offset cancellation.
• This results in an effective sensing range of 11 bits with 8-bit instrumentation.
• The system demonstrated a high-pass response between 2.3 - 3.8 mHz.

Conclusions:

• The mixed-signal offset cancellation loop effectively enhances the dynamic range of implanted pressure sensors.
• This digital approach is suitable for low-power, power-gated sensor applications.
• The technology is highly relevant for bio-sensing of slow physiological pressure changes, such as in the bladder.