Low Power Converter for Capacitive Sensors Using Capacitance-to-Pulse Width Modulation

• Main Authors: Balde, Arexius Vico, Owen Cabuyadao, John, Densing, Chris Vincent, Richard Hizon, John, Rosales, Marc, Maestro, Rico Jossel, Theresa de Leon, Maria
• Format: Conference Proceeding
• Language: English
• Subjects: Capacitance; Capacitors; Clocks; Dynamic range; Sensitivity; Sensors; Threshold voltage
• ISSN: 2159-3450
• DOI: 10.1109/TENCON.2018.8650155

This paper presents a low-power, low-area, and low complexity capacitance to pulse width (C-to-PWM) converter for capacitive sensors. The designed converter consists of a a clock generator, RC stage, comparator and XOR. The differential nature of the circuit produces square waves with pulse width proportional to the difference of the reference capacitance from the sensing capacitance. Moreover, the matched differential branches makes the output resilient to delays and jitters introduced by the blocks. The designed converter achieves a dynamic range of 1pF - 21.5pF at a sensitivity of 4.03µs/pF. Additionally, it is designed in 65nm CMOS technology and only consumes a maximum power of 256nW from a 1V supply at a frequency of 10.59kHz. The functionality of the circuit and the blocks involved are presented along with measurement results.