An RC Delay-Based Pressure-Sensing System With Energy-Efficient Bit-Level Oversampling Techniques for Implantable IOP Monitoring Systems

Abstract

A pressure-sensing system with a half-Wheatstone- bridge-to-digital converter (HBDC) is proposed for implantable intraocular pressure (IOP) monitoring systems. The half- Wheatstone-bridge (H-WhB) sensor uses an RC-delay comparison instead of direct bias of the pressure transducer, allowing it to self-limit the current for efficient operation. To overcome the limited sensitivity of the H-WhB, energy-efficient bit-level over- sampling (OS) is introduced. The system achieves 0.24-mmHg (1σ ) resolution with an 8.58-nJ· mmHg2 FOM and 12.79-µW power consumption with a 11.52-ms conversion time. This marks a 2.8× improvement in measured system power, 56.24× improvement in energy consumption, and 2.8× improvement in resolution compared to the prior H-WhB-based pressure sensor. In addition, the HBDC overcomes the low sensitivity limitations of the H-WhB and achieves a resolution FOM comparable to that of Wheatstone-bridge (WhB) sensor-based pressure sensors.