Abstract
This paper presents a new low-power high-resolution capacitive transducer for portable electrical capacitance tomography (ECT) applications. The mixed-signal transducer chip adopts a new switched-capacitor (SC) capacitance-to-voltage (CV) converter with stray immunity. The converter utilizes correlated double sampling (CDS) to minimize the 1/f noise and cancel the dc offset. Moreover, a new instrumentation-based methodology is realized through additional auto-zero (AZ) operations and two simple embedded sample-and-hold (S/H) circuitries to sample and cancel the front-end circuit level switch errors. With a high-resolution design objective, the design-for-test methodologies are also proposed, including the parasitic balancing technique and the charge lever mechanism. The simulation and measurement results validate the proposed methodologies and new circuit. The experimental results show that the transducer chip is able to sense the range of capacitance from 0.26 fF to 2 pF at a heavy parasitic capacitance of 150 pF, leading to a dynamic range of 77.8 dB at a single 3 V, while consuming a total of 4.5 mW. Compared with the reported works by several derived figures-of-merit, the IC prototype offers significant technical merits in terms of monolithic integration, a reduced power supply, low-power consumption, high resolution, and a high dynamic range.
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