Sviluppo di un sistema integrato general-purpose per l'interfacciamento di sensori ambientali e di specie chimiche

Sviluppo di una interfaccia integrata general-purpose per applicazioni con sensori ambientali e di specie chimiche. Il progetto, supportato dalla “Sensichips Srl” e sviluppato in collaborazione con l’Università di Padova e l’INFN di Cagliari, è nato con lo scopo di colmare la mancanza di queste tipologie di dispositivi nel mercato dei circuiti integrati. Ad oggi esistono infatti poche soluzione integrate rivolte all’interfacciamento di sensori, e per la maggior parte presentano delle limitazioni che non le rendono adatte ad un utilizzo general-purpose. L’architettura realizzata si distingue per una originale rete di generazione dei segnali di stimolo, che consente di trasferire ai DUT sia tensioni in DC, variabili all’interno dell’intero range di alimentazione, sia tensioni sinusoidali con frequenza variabile da 1Hz a 1MHz, e programmabile su 16 livelli di ampiezza. Per il canale di lettura è stata sviluppata una originale architettura di amplificatore da strumentazione, che garantisce una buona stabilità del guadagno differenziale per un range di modo comune di ingresso quasi rail-ro-rail. Misure sperimentali, effettuate sulle tre release del chip prodotte fino ad oggi, hanno dimostrato l’efficacia del sistema e la validità della soluzione proposta

Progetto di un Generatore Integrato di Stimoli per Impedenziometria

Progetto di un generatore integrato di stimoli per la lettura di informazioni da sensori di specie chimiche. E' stato sviluppato un sistema low-power e low-noise, in grado di generare stimoli in un range frequenziale da 1Hz a 1MHz. Possono essere generate rampe e tensioni sinusoidali, programmabili in ampiezza e valor medio. Il dispositivo è inoltre provvisto di un sistema di cancellazione dell'offest e di riduzione del rumore

Integrated smart gas flow sensor with 2.6 mW total power consumption and 80 dB dynamic range

A thermal flow sensor including sensing structures and a read-out interface in a single chip is proposed. The sensing structure is a microcalorimeter based on a double heater configuration while the low noise electronic interface performs signal reading and offset compensation. The device has been fabricated with a commercial CMOS process followed by a post-processing procedure. Post-processing has been customized in order to increase the thermal insulation of the sensing structures from the silicon substrate and improve the heat exchange between the sensor and the gas flow. Device characterization confirms the effectiveness of the proposed fabrication method in increasing the sensitivity at constant power consumption without affecting the dynamic range

Automatic compensation of pressure effects on smart flow sensors in the analog and digital domain

Two different approaches for the automatic compensation of pressure effects on thermal flow sensors are investigated. One approach operates in the analog domain and it is based on a closed-loop circuit that uses a pressure dependent signal to keep the sensor output constant. The digital approach operates in an open loop fashion and is capable of producing also a pressure reading. The effectiveness of the proposed methods has been verified by means of a smart flow sensor integrating on the same chip the sensing structures and a configurable electronic interface performing signal reading and non idealities compensation. The chip has been designed with a commercial CMOS process and fabricated by means of a post-processing technique. The experimental results performed in nitrogen confirm that both methods are capable of reducing the sensitivity of the flow sensor output signal to pressure variation

An integrated thermal sensor platform for multi-variable detection

A single chip sensor platform, including different kind of thermal sensors and advanced readout electronic circuits, is described. The chip is obtained using a two-step procedure: (i) the preliminary die is fabricated by a standard microelectronic process (STMicroelectronics BCD6s); (ii) post-processing is applied to the die to introduce thermal insulation between the sensor elements and the substrate. The sensors are finalized to detect flow rate, pressure and acoustical particle velocity. The electronic circuits include two low noise amplifiers and a programmable current source for sensor biasing

Integrated smart gas flow sensor with 2.6 mW total power consumption and 80 dB dynamic range

MEMS (Micro-Electro-Mechanical System) flow sensors based on a thermal principle allow detection of extremely small fluid flow rates with high accuracy and resolution [1]. Recently, considerable research effort is being spent to reduce the power consumption of these devices [2], following the requirements dictated by battery-powered platforms. In this work, we propose a thermal flow sensor, with integrated readout interface, designed to obtain a very low power consumption while maintaining a high dynamic range (DR), defined as the ratio between the maximum and minimum detectable flow. The device has been obtained by applying a post-processing micromachining procedure to chips fabricated with the STMicroelectronics BCD6s process. A photograph of the chip area is shown in Fig. 1, where the main blocks used in this work are indicated. The sensing structures are differential micro-calorimeters, consisting of two n-polysilicon/p-polysilicon thermopiles (4 mV/K sensitivity) symmetrically placed across two p-polysilicon resistive heaters (2 kW each). The sensor elements are placed on SiO2 membranes suspended over a cavity etched into the substrate in the post-processing phase. The heater driver feeds the heaters with two currents, whose differential component can be digitally tuned (10-bit resolution) to implement drift-free cancellation of the sensor offset [3]. The thermopile differential output voltage is amplified (gain=200) by the integrated low-noise, low-power chopper amplifier (In-Amp and oscillator blocks in Fig.1). A set of digital registers, which can be accessed by an embedded serial port, control the interface parameters. Selection of the sensors present on the chips occurs through an analog multiplexer. The sensing structure used in this work, indicated in Fig. 1, is optimized for low power consumption. This is obtained by reducing the thickness of the SiO2 membranes with respect to the total dielectric stack of the process, using an improved sensor design and post-processing approach with respect to the device described in Ref. [4]. In particular, the membranes have been defined with the second metal layer (Metal 2) instead of photoresist (Fig. 2a), exploiting the selectivity of the SiO2 etch in CF4 plasma towards aluminum. In this way, the metal mask is aligned during the chip design and all the dielectric layers above the Metal 2 are removed during the SiO2 etch (Fig. 2b) reducing the thickness of the suspended dielectric membranes with clear advantages in terms of thermal insulation. After the dielectric etch and the metal mask removal, the silicon substrate has been anisotropically etched in a TMAH solution (Fig. 2c). The chips are glued to ceramic DIL 28 packages and a PMMA (Poly-methyl-methacrylate) gas conveyor [4] is applied to the chip surface, obtaining the structure shown in Fig. 3. Note that the sensing structure is included into a flow channel with a 0.5 × 0.5 mm2 cross section. The response of the sensor to a nitrogen flow is shown in Fig. 4. The sensitivity is 13.2 mV/sccm, while the measured peak-to-peak output noise (over a 10 Hz bandwidth) is 0.2 mV. From these data, a resolution of 0.015 sccm (1 mm/s gas velocity) can be estimated. Considering the range of ± 100 sccm, the DR is nearly 82 dB. The heater current was set to around 0.3 mA, with a small differential component, applied to reduce the output offset to the same level as the output noise. The total current absorption of the chip, including the interface supply current, is 0.8 mA, which, at a supply voltage of 3.3 V, corresponds to a power consumption of 2.6 mW. The resolution by power-consumption product is 2.6 mW×mm/s, nearly three time higher (i.e. worse) than the sensors in [2], where, on the other hand, the amplifier supply current was not taken into account and a much smaller DR (26 dB) is reported

A compact low-noise fully differential bandgap voltage reference with intrinsic noise filtering

A new architecture for differential bandgap voltage references is presented. The system is based on a switched capacitor amplifier that performs correlated double sampling to cancel offset and reduce flicker noise while maintaining a valid output voltage throughout the clock cycle. The circuit noise is filtered by an intrinsic discrete time low-pass function with tunable cut-off frequency. A prototype designed with 0.18 um CMOS process is described. Preliminary performances are estimated by means of periodic noise analysis carried out with the SpectreRF simulator

A novel architecture for current-feedback instrumentation amplifiers with rail-to-rail input range

This paper presents a fully-differential currentfeedback instrumentation amplifier with rail-to-rail input common-mode (CM) voltage range. Gm mismatches due to input CM variations have been reduced exploiting an original commonmodes equalization loop. Chopping modulation is adopted to improve the performances of the amplifier in terms of offset and low frequency noise, while the intrinsic low-pass transfer function of the amplifier is exploited for the reduction of the offset-ripple. A prototype has been designed using the UMC 0.18um MM/RF CMOS process. Simulations, performed with a supply voltage of 1.5 V, showed that a maximum relative gain error of nearly ±1.5 %, against rail-to-rail input CM voltage variations, can be achieved

A continuous time switched capacitor DAC with offset and flicker noise cancellation

A switched capacitor DAC, capable of producing a continuous time output signal, is presented. The multiphase conversion cycle allows cancellation of the input offset and low frequency noise of both op-amps used in the circuit. Electrical simulations, performed on a 12 bit prototype, designed by means of UMC 0.18 um MM/RF CMOS process, are shown. The main estimated performances are: 2.4 us conversion time, 0.42 mW power consumption at 1.8 V power supply, 0.49 mV rms output noise over a 400 kHz bandwidt

Experimental characterization of a novel single chip flow sensor with automatic compensation of pressure effects

A smart flow sensor fabricated on a single chip with a commercial CMOS process followed by a post-processing technique is characterized. The sensing structures are micro-calorimeters made up of two heaters placed between an upstream and a downstream temperature probe. The integrated read-out electronics performs the automatic compensation of intrinsic offset and pressure effects. The effectiveness of the proposed correction methods is verified in nitrogen at room temperature