Signal Conditioning Circuits for Injectable Pressure Sensors

The pressure at different organs is highly regulated in the human body, which is a key indicator of health in many chronic conditions. Monitoring these pressures remotely and precisely provides useful information for managing health and treating disease. To measure these pressures, less invasive and miniaturized implantable devices are required. Creating highly miniaturized pressure sensors would allow them to be deployed by minimally invasive methods such as an injectable pressure sensor. However, creating injectable sensors requires highly integrated pressure sensor signal conditioning circuits to be developed as current methods are larger than those that can be included in an injectable device. Miniaturization to this level is only possible through creating an ASIC which includes all functions to allow sensor readout, power reception and data transfer. This work investigated a low-power, injectable pressure sensor readout ASIC in a 180 nm CMOS process to support injectable capacitive pressure sensors. The ASIC was developed in a step-by-step process with three fabrication runs of XFAB XH018 CMOS which allowed subcircuits to be tested throughout the development and to achieve the design of a pressure sensor readout ASIC. The first ASIC, a capacitance to frequency converter ASIC was designed, fabricated and tested which confirmed the function of 1.8V LDO, bandgap, oscillator and VCO circuits with a wirelessly powered PCB coil. Then, a second ASIC was designed to improve the accuracy of the first ASIC using a new switched-capacitor (SC) analog front end (AFE) and a SC single-slope ADC with an inductive wireless power supply and load shift keying (LSK) for a wireless data transfer, which was also fabricated and tested. It confirmed the function of the SC AFE (capacitance to voltage), I2C, 500 kHz RC oscillator, 2.5V HV LDO and LSK circuits. The third ASIC corrected an issue identified in the second ASIC testing where logic errors lead to corruption of the digital data in the single-slope ADC. Finally, a complete system ASIC that met all requirements was designed and fabricated with the major addition being the incorporation of a 19-bit capacitance to digital converter utilizing a Δ∑ADC. The ASIC was evaluated for accuracy and power consumption in a custom-designed bench top rig which incorporated a pressure-controlled environment, a wireless power transfer system and a data receiver implemented in a Field Programmable Gate Array (FPGA). This confirmed the ASIC met the technical requirements of injectable pressure sensors. In summary, three different types of pressure sensor readout ASIC were fabricated and tested. The final ASIC had a 265 μW power consumption at 1.8 V power supply and 575–900 mmHg absolute measuring range with a better than 1 mmHg accuracy. This ASIC is a key step towards the development of high precision wireless injectable pressure sensors for applications such as Intracranial Pressure (ICP), compartment and cardiovascular pressure monitoring.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Bioengineering

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2021

Author dc:creator

• Zhang, Chaoping (Cooper)

Advisors dc:contributor.advisor

• McCormick, Daniel
• Gallichan, Robert John
• Budgett, David

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/60634

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/60634