A 180-nm CMOS Integrated Capacitance-to-Time Converter for Capacitive Sensing Applications
This article presents the implementation of a capacitance-to-time converter in standard 0.18-μm CMOS technology. It is based on a square-wave relaxation oscillator that incorporates both pulsewidth modulation (PWM) and proportional to magnitude (PM) dependencies. The circuit is designed to interface...
| Authors: | , , , , , |
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| Format: | article |
| Status: | Published version |
| Publication Date: | 2025 |
| Country: | España |
| Institution: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repository: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/409996 |
| Online Access: | http://hdl.handle.net/10261/409996 https://api.elsevier.com/content/abstract/scopus_id/105013339274 |
| Access Level: | Open access |
| Keyword: | Capacitance-to-time converter CMOS integrated circuit Differential capacitance sensors |
| Summary: | This article presents the implementation of a capacitance-to-time converter in standard 0.18-μm CMOS technology. It is based on a square-wave relaxation oscillator that incorporates both pulsewidth modulation (PWM) and proportional to magnitude (PM) dependencies. The circuit is designed to interface with differential capacitance sensors but can also interface with single-capacitance sensors using a reference capacitor. It works with various capacitive values, ranging from a few nanofarads to less than one picofarad, considering different external R<inf>0</inf> resistor values. Characterization tests proved that the fabricated chips exhibit the expected performance across the full range of use, achieving a sensitivity of 207 μs/ΔpF in the differential mode (110 μs/pF in the single mode) and a resolution of 0.5 fF in the differential mode ((0.9 fF in the single mode). The circuit occupies a silicon area of 0.0044mm<sup>2</sup>, with a maximum power consumption of 1.5 mW. The circuit has also been successfully tested in real applications, such as measuring liquid levels in microfluidic applications. By using COTS level-meters, it achieved a sensitivity of 0.4 pF/mL with a resolution of 100 μL. Measuring the dielectric constant in liquids was also demonstrated by using specifically designed 3-D-printed fluidic capacitance sensors. |
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