首页|Multi-Bit Capacitance Sensing System Using a-IGZO TFT Technology for Smart Wearables
Multi-Bit Capacitance Sensing System Using a-IGZO TFT Technology for Smart Wearables
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NETL
NSTL
IEEE
This brief presents a novel multi-bit Capacitance-to-Digital converter (CDC) using unipolar single-gate amorphous-Indium-Gallium-Zinc-Oxide thin-film transistors (a-IGZO TFTs). This circuit is fabricated on a $30{\mathrm {\,}} \mu $ m thick polyimide substrate with an active area of $6.5{\mathrm {\,}}$ mm2. The proposed CDC is designed by employing Charge-Sharing Successive-Approximation Register Analog-to-Digital Converter (CS SAR ADC). Further, the design facilitates integration of capacitance sensor/array directly with the ADC, hence the additional interfacing circuits between the capacitive-sensor and the ADC can be eliminated to make the system compact and energy-efficient. The functionality of the proposed CDC is demonstrated for a sensor capacitance value ranging from $1{\mathrm {\,}}$ pF to $31{\mathrm {\,}}$ pF. From measurements it is observed that the minimum value of capacitance that can be detected with the proposed CDC is around $2{\mathrm {\,}}$ pF, while the state-of-the-art CDC is around $3.7{\mathrm {\,}}$ pF, which is reported on a truly flexible substrate. Further, the ADC deployed in the CDC has resulted in an SNR of $35.57{\mathrm {\,}}$ dB, figure-of-merit (FoM) of $19.9{\mathrm {\,}}$ nJ/c.s., ENOB of $5.6{\mathrm {\,}}$ bits, differential non-linearity (DNL) of $0.52{\mathrm {\,}}$ LSB and an integral non-linearity (INL) of $0.81{\mathrm {\,}}$ LSB. At a sampling frequency of $2.08{\mathrm {\,}}$ kHz, the ADC has shown a total power dissipation of $2.02{\mathrm {\,}}$ mW with a supply voltage $(V_{DD})$ of $4{\mathrm {\,}}$ V. This capacitance sensing system finds potential applications in areas of biomedical, healthcare, and smart packaging systems etc, which need truly flexible devices.
CapacitanceCapacitorsSensorsLogicVoltageVirtual private networksThin film transistorsTransistorsSubstratesControl systems
Bhawna Tiwari、Suyash Shrivastava、Vaishali Choudhary、Pydi Ganga Bahubalindruni
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Department of Electrical Engineering and Computer Science, IISER Bhopal, Bhopal, India
NETL
NSTL
IEEE
