A Compact, Dual Channel Flow-based Differential Pressure Sensor with mPa Resolution and Sub-10 mW Power Consumption

In this work, we propose a single-chip sensor for the detection of two extremely low, independent differential pressures. The operating principle consists in measuring the airflow induced by the pressure through a channel of sub-millimeter cross-section [1]. The airflow is measured by differential thermal flow sensors, implementing a recently proposed drift-free offset compensation approach. Use of a low-noise, low-power readout interface, integrated on the same chip as the sensing structures, allowed the achievement of resolutions of 1.29 mPa, which are one order of magnitude lower than state-of-art devices. This performance has been obtained with power consumptions suitable for battery-powered applications

Precise measurement of gas volumes by means of low-offset MEMS flow sensors with µL/min resolution

Experiments devoted to evaluate the performance of a MEMS thermal flow sensor in measuring gas volumes are described. The sensor is a single-chip platform, including several sensing structures and a low-offset, low-noise readout interface. A recently proposed offset compensation approach is implemented obtaining low temperature drift and excellent long time stability. The sensor is fabricated by applying a simple micromachining procedure to a chip produced using the BCD6s process of STMicroelectronics. Application of a gas conveyor allowed inclusion of the sensing structure into a channel of sub-millimeter cross-section. The results of measurements performed by making controlled air volumes pass through the sensor channel in both directions at rates from 0.1 to 5 mL/min are described

A Compact CMOS Compatible micro-Pirani Vacuum Sensor with Wide Operating Range and Low Power Consumption

A micro-Pirani vacuum sensor with an operating pressure range of more than 5 decades is described. The device is fabricated by applying a low-resolution and potentially low-cost front-side bulk micromachining step to a chip produced with a commercial CMOS technology. Maximization of the thermally coupled surfaces has been obtained by stacking all layers available by default in the CMOS process. This design choice and the integration of a low-noise, low-power readout interface allowed achievement of state-of-art performances with a fabrication approach affordable even to SMEs and small University laboratories

A compact current-mode instrumentation amplifier for general-purpose sensor interfaces

The proposed amplifier architecture follows a consolidated topology based on second-generation current conveyors (CCIIs), optimized for fully-differential operation. The architecture uses gain-boosting to improve the offset and noise characteristics of a recently proposed design. Wide input and output ranges and high accuracy are obtained by designing the CCIIs according to an original two-stage architecture with local voltage feedback. Embedding of chopper switch matrices into the amplifier enables vector analysis of the input signal, expanding the application field. The main strengths of the proposed amplifier are compactness and versatility. Measurements performed on a prototype designed with a 0.18 μm CMOS process are described

Progetto di una interfaccia per sensori capacitivi a bassissimo consumo in tecnologia CMOS 0.18um

Progetto di interfaccia per sensori capacitivi a bassissimo consumo con specifiche di bassa deriva dermica delle prestazioni

DESIGN OF A VERSATILE, FULLY-INTEGRATED SENSOR INTERFACE IN A 0.18 um CMOS TECHNOLOGY

In the last decades the number of sensors involved in everyday life has been quickly increased. The growing demand of more accurate sensors and more complex sensors networks, shown both by consumer and industrial markets, is currently driving the development of innovative solutions to maximise the data collected from the environment. In particular, sensors are devices that convert a physical quantity, such as temperature, humidity or pressure, in an electrical one, enabling the measurement of environmental parameters. Every one requires a dedicated read-out front-end that, depending on the sensor nature, has to properly stimulate it and sense its output signal without affecting it. However, in modern applications, such as the Internet of Things ones, the reduced available silicon area and the use of battery supplies strongly limit the number of front-ends embedded in a single device as well the number and variety of sensors that could be measured by a single device. To overcome this issue, in the last years researchers made lots of effort in designing general-purpose sensor interfaces capable of properly stimulate and sense different kind of sensors. However, most of the proposed in the literature interfaces lack of some functionalities. For example, some devices are capable of performing only DC measurements, or they are not suitable for four-contact set-ups. On the contrary, others solutions, such as the AD5933 [1] of Analog Devices, are capable of executing DC and AC measurements but the operating frequencies range is smaller than required in many applications. In addition, many of them are not compliant with modern micro-controller families and with single cell battery supplies because of a too high minimum required supply voltage. To cope with all these specifications, since 2012 the Sensichips s.r.l., in partnership with the Department of Information Engineering of the University of Pisa, is developing a novel general-purpose sensor interface, the Sensiplus. The Sensiplus interface is a compact standalone System on a Chip (1.5 mm x 1.5 mm only) which properly operates from 1.5 V up to 3.3 V of supply voltage with a quiescent current consumption of only 50 A. It is suitable for a wide number of measurements, including the AC voltammetry and the Electrical Impedance Spectroscopy, resulting capable of interfacing a large variety of sensors. In particular, the Sensiplus embeds up to 15 integrated sensors, including temperature, light and functionalisable ones, and it could be connected up to 7 different external sensors. The research activity presented in this thesis started during the development of the Sensiplus fourth release and consists in the design of three main blocks of the interface: a new stimulus generator, an innovative Ripple Reduction Loop to be embedded within the Instrumentation Amplifier, and an improved version of the digital core. These IPs were integrated in the fourth, fifth and sixth device release in order to validate their performances by means of electrical measurements

A CMOS compatible micro-Pirani vacuum sensor based on mutual heat transfer with 5-decade operating range and 0.3 Pa detection limit

A Pirani vacuum sensor based on mutual heating between a heater and a distinct temperature probe, separated by a 5 μm air gap, is proposed. The sensor is fabricated by applying a simple post-processing procedure to chips designed and fabricated using the BCD6s process (Bipolar-CMOS-DMOS) of STMicroelectronics. The sensor layout has been optimized to exploit the layers of the original process in order to enhance the sensor performance. The sensors exhibit a resolution better than 0.4 Pa from nearly 0.3 Pa to 1 kPa and better than 50 Pa from 1 kPa to 100 kPa. The sensor response at the lower extreme of the pressure interval is marked by an offset voltage, which is three orders of magnitude smaller than the full-scale value. Finite Element Method simulations suggest that the offset is due to pressure-independent heat transfer due to radiation and conduction through the substrate. The simulated equivalent offset drift is 50 MPa/K

Integrated thermal flow sensors with programmable power-sensitivity trade-off

A thermal flow sensor integrated with a programmable electronic interface into the same chip is proposed. The sensing structure is a micro-calorimeter with a double heater configuration fabricated with a simple post-processing technique applied to chip designed with a commercial CMOS process. The electronic interface is based on a low-noise, low-power instrumentation amplifier and a configurable heater current driver. The device characterization in nitrogen confirms the possibility to manage the trade-off between the sensitivity and the power delivered to the device by means of the programmable interface

A chopper stabilized, low power capacitance to PWM converter for sensor interfacing

A low-power, low voltage capacitance to pulse duration converter with intrinsic low sensitivity to temperature and parasitic capacitances is presented. The circuit uses a dual clock chopper modulation, which significantly lowers the effects of device mismatch. An effective resolution of 7.2 bits with 3.8 uA supply current and operation down to 0.9 Vdd are demonstrated by means of electrical simulations performed on a prototype designed with the UMC 0.18 um process

A compact programmable differential voltage reference with unbuffered 4 mA output current capability and ±0.4 % untrimmed spread

A compact differential voltage reference cell, which combines an original switched capacitor integrator with a digitally programmable bandgap core, is presented. The two-stage integrator maintains an always-valid output voltage while performing correlated double sampling to effectively reduce the effects of offset and flicker noise. Measurements performed on a prototype designed with the UMC 0.18 um CMOS process showed a ±0.4 % untrimmed output voltage spread, 1 Hz flicker noise corner and output current capability of up to 4 mA with a quiescent current consumption of 50 uA