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A compact sensor readout circuit with combined temperature, capacitance and voltage sensing functionality
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2017
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EngineeringVoltage SensingAnalog DesignSensor InterfaceIntegrated CircuitsShared Zoom AdcSensor TechnologyImage SensorDie AreaCalibrationInstrumentationVoltage Sensing FunctionalityOn-chip SensorsAnalog-to-digital ConverterElectrical EngineeringData ConverterComputer EngineeringCombined TemperatureMicroelectronicsBiomedical SensorsSensorsSensor DesignThermal Sensor
The authors propose an area‑ and energy‑efficient readout circuit capable of simultaneously digitizing temperature, capacitance, and voltage. The design employs a shared zoom ADC that combines SAR and ΔΣ conversion with on‑chip references to reduce die area. Tests on 24 wafer samples show temperature accuracy of ±0.2 °C over –55 °C to 125 °C, voltage accuracy of ±0.5 %, 18.7‑ENOB capacitance conversion up to 3.8 pF, 0.76 pJ per conversion‑step energy efficiency, 0.33 mm² area, and 4.6 µA current at 1.8 V.
This paper presents an area- and energy-efficient sensor readout circuit, which can precisely digitize temperature, capacitance and voltage. The three modes use only on-chip references and employ a shared zoom ADC based on SAR and ΔΣ conversion to save die area. Measurements on 24 samples from a single wafer show a temperature inaccuracy of ±0.2 °C (3σ) over the military temperature range (−55°C to 125°C). The voltage sensing shows an inaccuracy of ±0.5%. The sensor also offers 18.7-ENOB capacitance-to-digital conversion, which handles up to 3.8 pF capacitance with a 0.76 pJ/conv.-step energy-efficiency FoM. It occupies 0.33 mm in a 0.16 μm CMOS process and draws 4.6 μA current from a 1.8 V supply.