Federico Butti

A Low-Power Interface for Capacitive Sensors With PWM Output and Intrinsic Low Pass Characteristic

A compact, low power interface for capacitive sensors, is described. The output signal is a pulse width modulated (PWM) signal, where the pulse duration is linearly proportional to the sensor differential capacitance. The original conversion approach consists in stimulating the sensor capacitor with a triangular-like voltage waveform in order to obtain a square-like current waveform, which is subsequently demodulated and integrated over a clock period. The charge obtained in this way is then converted into the output pulse duration by an approach that includes an intrinsic tunable low pass function. The main non idealities are thoroughly investigated in order to provide useful design indications and evaluate the actual potentialities of the proposed circuit. The theoretical predictions are compared with experimental results obtained with a prototype, designed and fabricated using 0.32 μm CMOS devices from the BCD6s process of STMicroelectroncs. The prototype occupies a total area of 1025× 515 mm2 and is marked by a power consuption of 84 μW. The input capacitance range is 0-256 fF, with a resolution of 0.8 fF and a temperature sensitivity of 300 ppm/°C.

Smart Flow Sensor With On-Chip CMOS Interface Performing Offset and Pressure Effect Compensation

A single-chip smart flow sensor based on a thermal principle is presented. The device is fabricated through a commercial complementary metal-oxide-semiconductor (CMOS) process combined with a postprocessing procedure. A configurable electronic interface performing signal reading and nonideality compensation is integrated with the sensing structures on the same chip. The interface implements recently proposed approaches to offset and pressure effect compensation. Detailed experimental results are presented demonstrating correct operation of the proposed microsystem.

CMOS compatible acoustic particle velocity sensors

In this work we propose 2D acoustical particle velocity (APV) sensors produced by post processing silicon chips designed with the STMicroelectronics 0.32 µm BCD6s process. The sensors consist of two conductive wires suspended on dielectric membranes, separated by a 10 µm air gap. Heat exchange between the wires, heated by an electrical current, is modulated by the local velocity of the medium, producing temperature oscillations, which are transformed into voltage oscillations by the wire temperature coefficient of resistance (TCR). Experimental characterization of the sensors, based on the standing wave tube method, is presented.

Acoustic Velocity Sensors with Programmable Directivity

A directional acoustical sensor with programmable axis of maximum sensitivity is described. The sensor is based on a combination of two orthogonal acoustical particle velocity (APV) sensors, integrated on the same chip. The APV sensors are based on a thermal transduction principle. Differently from former implementations, the proposed devices are fully CMOS compatible. Rotation of the sensitivity axis is obtained by combining the output of the two APV sensors properly weighted with programmable coefficients. This operation is performed using a microcontroller ADuC842 (Analog Devices) equipped with 12 bit, 400 kS ADCs.

17.5 A 0.07mm 2 2-channel instrumentation amplifier with 0.1% gain matching in 0.16μm CMOS

Extremely small-area sensor front-ends are required for cost-constrained automotive applications. Instrumentation amplifiers (IA) for such front-ends must process multi-channel sensor outputs and provide gain matching over the channels for proper sensor operation. Angular sensors are a typical example, in which the sine and cosine outputs of a resistive magnetic sensor must be processed with adequate gain matching to avoid unacceptable angular errors. This paper presents a 2-channel instrumentation amplifier in 0.16μm CMOS with 0.1% gain matching and occupying 0.035mm2 per channel. This represents a 13.3× area improvement with respect to state-of-the-art designs with similar gain accuracy [1]-[4], while maintaining low noise (18.7nV/√Hz), low offset (17μV) and high power efficiency (NEF=12.9). The accurate gain matching in a limited area is enabled by the adoption of a dynamic element matching (DEM) scheme and by the use of a high chopping frequency.

A chopper modulated low noise instrumentation amplifier for MEMS thermal sensors interfacing

A CMOS instrumentation amplifier for interfacing integrated thermal sensors is proposed. It is based on a Gm-C 2nd order low pass filter, and exploits chopper modulation to improve its performances in terms of offset and low frequency noise. An input noise level of 10 nV/sqrt(Hz) and a current consumption of a few hundred of μA have been obtained by means of a careful design. Moreover, an original technique of input and feedback port swapping improves the amplifier gain precision. A prototype has been designed with the BCD6s STMicroelectronics process, and its functionality has been demonstrated by means of electrical simulations.

Smart Flow Sensors Based on Advanced Packaging Techniques Applied to Single Chip Sensing Devices

A smart flow sensor capable of measuring two distinct gas flows with two different linearity ranges is proposed. The device is based on a chip, designed with a commercial CMOS process, which includes different sensing structures and a read-out interface. The chip is fabricated applying a post-processing technique based on a silicon anisotropic etching in a TMAH solution. A simple and low cost packaging technique is used to convey two distinct gas flows to two selected sensing structures by means of channels of different cross sections. Three methods for sealing the interface between the chip and the gas conveyor are proposed and discussed.

A low power CMOS capacitance to pulse duration converter based on a dual clock approach

An interface for integrated capacitive sensors producing a PWM signal is presented. The circuit is based on a recently proposed architecture, which is here improved by the introduction of a double clock strategy allowing jitter reduction. The non idealities of the circuit are investigated in order to obtain design criteria to reduce the jitter and the temperature dependence. The approach is validated with electrical simulations performed on a prototype designed with devices from the 0.32 μm CMOS subset of the STMicroelectronics BCD6s process.

Compact Low Noise Interfaces for Multichannel MEMS Thermal Sensors

In this work a novel architecture for the design of compact instrumentation amplifier is described. The low offset and low noise characteristics of the proposed amplifier make it particularly suitable for interfacing thermopile-based MEMS sensors. The circuit consists in a fully differential 2nd order low pass Gm-C filter, properly modified to provide gain and incorporate chopper modulation. The validity of the approach is proven by means of simulations performed on a prototype designed with a commercial CMOS process.

Acoustic Particle Velocity Sensors Based on a Thermal Principle

A new integrated sensor for the acoustic particle velocity measurement is proposed. The device is based on a thermal principle and is made up of two polysilicon heaters placed over suspended dielectric membranes. The sensor is fabricated by means of a post-processing technique applied to chips designed with a commercial CMOS process. Preliminary measurements confirm the device suitability for acoustic applications.