Interface Circuits for Microsensor Integrated Systems

ca. 200 words; this text will present the book in all promotional forms (e.g. flyers). Please describe the book in straightforward and consumer-friendly terms. [Recent advances in sensing technologies, especially those for Microsensor Integrated Systems, have led to several new commercial applications. Among these, low voltage and low power circuit architectures have gained growing attention, being suitable for portable long battery life devices. The aim is to improve the performances of actual interface circuits and systems, both in terms of voltage mode and current mode, in order to overcome the potential problems due to technology scaling and different technology integrations. Related problems, especially those concerning parasitics, lead to a severe interface design attention, especially concerning the analog front-end and novel and smart architecture must be explored and tested, both at simulation and prototype level. Moreover, the growing demand for autonomous systems gets even harder the interface design due to the need of energy-aware cost-effective circuit interfaces integrating, where possible, energy harvesting solutions. The objective of this Special Issue is to explore the potential solutions to overcome actual limitations in sensor interface circuits and systems, especially those for low voltage and low power Microsensor Integrated Systems. The present Special Issue aims to present and highlight the advances and the latest novel and emergent results on this topic, showing best practices, implementations and applications. The Guest Editors invite to submit original research contributions dealing with sensor interfacing related to this specific topic. Additionally, application oriented and review papers are encouraged.

A mixed-signal control system for Lorentz-force resonant MEMS magnetometers

This paper presents a mixed-signal closed-loop control system for Lorentz force resonant MEMS magnetometers. The control system contributes to 1) the automatic phase control of the loop, that allows start-up and keeps self-sustained oscillation at the MEMS resonance frequency, and 2) output offset reduction due to electrostatic driving by selectively disabling it. The proposed solution proof-of-concept has been tested with a Lorentz force-based MEMS magnetometer. The readout electronic circuitry has been implemented on a printed circuit board with off-the-shelf components. Digital control has been implemented in an FPGA coded with VHDL. When biased with 1 V and a driving current of 300 µArms, the device shows 9.75 pA/µT sensitivity and total sensor white noise of 550 nT/vHz. Offset when electrostatic driving is disabled is 793 µT, which means a 40.1% reduction compared when electrostatic driving is enabled. Moreover, removing electrostatic driving does not worsen bias instability, which is lower than 125 nT in both driving cases.Peer ReviewedPostprint (published version

New mathematical formulation for designing a fully differential self-biased folded cascode amplifier

One of the most important building blocks in analog circuit design is the operational amplifiers. This is because of their versatility and wide spread usage in many applications such as communications transmitters and receivers, analog to digital converters, or any other application that requires a small signal to be amplified. The basic amplifier topologies are introduced. Then, some operational amplifiers topologies are introduced with some techniques to self bias these amplifiers. The folded cascode fully differential Op-Amp with self bias is presented. This is one of the newest amplifier topologies which provide stable self-biased amplifiers. A new mathematical model for fully differential folded cascode amplifiers is presented and generalized to include the family of fully differential complementary amplifiers. This formulation focuses on deriving detailed design equations for the amplifier gain and frequency response. The equations are verified through time domain and frequency domain simulations of different fabrication processes to ensure the validity of the model across a wide range of processes. The model was verified against TMSC 180nm, 250nm, and 350nm fabrication processes. The new model agrees well with simulations; with 1% error for the amplifier gain and \u3c7% error for amplifier bandwidth. The relatively high error value for the bandwidth is because the model considers the worst case scenario and overestimates the output capacitance. Finally, the algorithm of getting this formulation is extended to include special and commonly used cases. This formulation proved to be very useful in designing stable, self-biased, fully differential folded cascode amplifiers

Doctor of Philosophy

dissertationThis thesis presents the design, fabrication and characterization of a microelectromechanical system (MEMS) based complete wireless microsystem for brain interfacing, with very high quality factor and low power consumption. Components of the neuron sensing system include TiW fixed-fixed bridge resonator, MEMS oscillator based action-potential-to-RF module, and high-efficiency RF coil link for power and data transmissions. First, TiW fixed-fixed bridge resonator on glass substrate was fabricated and characterized, with resonance frequency of 100 - 500 kHz, and a quality factor up to 2,000 inside 10 mT vacuum. The effect of surface conditions on resonator's quality factor was studied with 10s of nm Al2O3 layer deposition with ALD (atomic layer deposition). It was found that MEMS resonator's quality factor decreased with increasing surface roughness. Second, action-potential-to-RF module was realized with MEMS oscillator based on TiW bridge resonator. Oscillation signal with frequency of 442 kHz and phase noise of -84.75 dBc/Hz at 1 kHz offset was obtained. DC biasing of the MEMS oscillator was modulated with neural signal so that the output RF waveform carries the neural signal information. Third, high-efficiency RF coil link for power and data communications was designed and realized. Based on the coupled mode theory (CMT), intermediate resonance coil was introduced and increased voltage transfer efficiency by up to 5 times. Finally, a complete neural interfacing system was demonstrated with board-level integration. The system consists of both internal and external systems, with wireless powering, wireless data transfer, artificial neuron signal generation, neural signal modulation and demodulation, and computer interface displaying restored neuron signal

System-on-Package Low-Power Telemetry and Signal Conditioning unit for Biomedical Applications

Recent advancements in healthcare monitoring equipments and wireless communication technologies have led to the integration of specialized medical technology with the pervasive wireless networks. Intensive research has been focused on the development of medical wireless networks (MWN) for telemedicine and smart home care services. Wireless technology also shows potential promises in surgical applications. Unlike conventional surgery, an expert surgeon can perform the surgery from a remote location using robot manipulators and monitor the status of the real surgery through wireless communication link. To provide this service each surgical tool must be facilitated with smart electronics to accrue data and transmit the data successfully to the monitoring unit through wireless network. To avoid unwieldy wires between the smart surgical tool and monitoring units and to reap the benefit of excellent features of wireless technology, each smart surgical tool must incorporate a low-power wireless transmitter. Low-power transmitter with high efficiency is essential for short range wireless communication. Unlike conventional transmitters used for cellular communication, injection-locked transmitter shows greater promises in short range wireless communication. The core block of an injection-locked transmitter is an injection-locked oscillator. Therefore, this research work is directed towards the development of a low-voltage low-power injection-locked oscillator which will facilitate the development of a low-power injection-locked transmitter for MWN applications. Structure of oscillator and types of injection are two crucial design criteria for low-power injection-locked oscillator design. Compared to other injection structures, body-level injection offers low-voltage and low-power operation. Again, conventional NMOS/PMOS-only cross-coupled LC oscillator can work with low supply voltage but the power consumption is relatively high. To overcome this problem, a self-cascode LC oscillator structure has been used which provides both low-voltage and low-power operation. Body terminal coupling is used with this structure to achieve injection-locking. Simulation results show that the self-cascode structure consumes much less power compared to that of the conventional structure for the same output swing while exhibiting better phase noise performance. Usage of PMOS devices and body bias control not only reduces the flicker noise and power consumption but also eliminates the requirements of expensive fabrication process for body terminal access

High performance readout circuits and devices for Lorentz force resonant CMOS-MEMS magnetic sensors

In the last decades, sensing capabilities of martphones have greatly improved since the early mobile phones of the 90’s. Moreover, wearables and the automotive industry require increasing electronics and sensing sophistication. In such echnological advance, Micro Electro Mechanical Systems (MEMS) have played an important role as accelerometers and gyroscopes were the first sensors based on MEMS technology massively introduced in the market. In contrast, it still does not exist a commercial MEMS-based compass, even though Lorentz force MEMS magnetometers were first proposed in the late 90’s. Currently, Lorentz force MEMS magnetometers have been under the spotlight as they can offer an integrated solution to nowadays sensing power. As a consequence, great advances have been achieved, but various bottlenecks limit the introduction of Lorentz force MEMS compasses in the market. First, current MEMS magnetometers require high current consumption and high biasing voltages to achieve good sensitivities. Moreover, even though devices with excellent performance and sophistication are found in the literature, there is still a lack of research on the readout electronic circuits, specially in the digital signal processing, and closed loop control. Second, most research outcomes rely on custom MEMS fabrication rocesses to manufacture the devices. This is the same approach followed in current commercial MEMS, but it requires different fabrication processes for the electronics and the MEMS. As a consequence, manufacturing cost is high and sensor performance is affected by the MEMS-electronics interface parasitics. This dissertation presents potential solutions to these issues in order to pave the road to the commercialization of Lorentz force MEMS compasses. First, a complete closed loop, digitally controlled readout system is proposed. The readout circuitry, implemented with off-the-shelf commercial components, and the digital control, on an FPGA, are proposed as a proof of concept of the feasibility, and potential benefits, of such architecture. The proposed system has a measured noise of 550 nT / vHz while the MEMS is biased with 300 µA rms and V = 1 V . Second, various CMOS-MEMS magnetometers have been designed using the BEOL part of the TSMC and SMIC 180 nm standard CMOS processes, and wet and vapor etched. The devices measurement and characterisation is used to analyse the benefits and drawbacks of each design as well as releasing process. Doing so, a high volume manufacturing viability can be performed. Yield values as high as 86% have been obtained for one device manufactured in a SMIC 180 nm full wafer run, having a sensitivity of 2.82 fA/µT · mA and quality factor Q = 7.29 at ambient pressure. While a device manufactured in TSMC 180 nm has Q = 634.5 and a sensitivity of 20.26 fA/µT ·mA at 1 mbar and V = 1 V. Finally, an integrated circuit has been designed that contains all the critical blocks to perform the MEMS signal readout. The MEMS and the electronics have been manufactured using the same die area and standard TSMC 180 nm process in order to reduce parasitics and improve noise and current consumption. Simulations show that a resolution of 8.23 µT /mA for V = 1 V and BW = 10 Hz can be achieved with the designed device.En les últimes dècades, tenint en compte els primers telèfons mòbils dels anys 90, les capacitats de sensat dels telèfons intel·ligents han millorat notablement. A més, la indústria automobilística i de wearables necessiten cada cop més sofisticació en el sensat. Els Micro Electro Mechanical Systems (MEMS) han tingut un paper molt important en aquest avenç tecnològic, ja que acceleròmetres i giroscopis varen ser els primers sensors basats en la tecnologia MEMS en ser introduïts massivament al mercat. En canvi, encara no existeix en la indústria una brúixola electrònica basada en la tecnologia MEMS, tot i que els magnetòmetres MEMS varen ser proposats per primera vegada a finals dels anys 90. Actualment, els magnetòmetres MEMS basats en la força de Lorentz són el centre d'atenció donat que poden oferir una solució integrada a les capacitats de sensat actuals. Com a conseqüència, s'han aconseguit grans avenços encara que existeixen diversos colls d'ampolla que encara limiten la introducció al mercat de brúixoles electròniques MEMS basades en la força de Lorentz. Per una banda, els agnetòmetres MEMS actuals necessiten un consum de corrent i un voltatge de polarització elevats per aconseguir una bona sensibilitat. A més, tot i que a la literatura hi podem trobar dispositius amb rendiments i sofisticació excel·lents, encara existeix una manca de recerca en el circuit de condicionament, especialment de processat digital i control del llaç. Per altra banda, moltes publicacions depenen de processos de fabricació de MEMS fets a mida per fabricar els dispositius. Aquesta és la mateixa aproximació que s'utilitza actualment en la indústria dels MEMS, però té l'inconvenient que requereix processos de fabricació diferents pels MEMS i l’electrònica. Per tant, el cost de fabricació és alt i el rendiment del sensor queda afectat pels paràsits en la interfície entre els MEMS i l'electrònica. Aquesta tesi presenta solucions potencials a aquests problemes amb l'objectiu d'aplanar el camí a la comercialització de brúixoles electròniques MEMS basades en la força de Lorentz. En primer lloc, es proposa un circuit de condicionament complet en llaç tancat controlat digitalment. Aquest s'ha implementat amb components comercials, mentre que el control digital del llaç s'ha implementat en una FPGA, tot com una prova de concepte de la viabilitat i beneficis potencials que representa l'arquitectura proposada. El sistema presenta un soroll de 550 nT / vHz quan el MEMS està polaritzat amb 300 µArms i V = 1 V . En segon lloc, s'han dissenyat varis magnetòmetres CMOS-MEMS utilitzant la part BEOL dels processos CMOS estàndard de TSMC i SMIC 180 nm, que després s'han alliberat amb líquid i gas. La mesura i caracterització dels dispositius s’ha utilitzat per analitzar els beneficis i inconvenients de cada disseny i procés d’alliberament. D'aquesta manera, s'ha pogut realitzar un anàlisi de la viabilitat de la seva fabricació en massa. S'han obtingut valors de yield de fins al 86% per un dispositiu fabricat amb SMIC 180 nm en una oblia completa, amb una sensibilitat de 2.82 fA/µT · mA i un factor de qualitat Q = 7.29 a pressió ambient. Per altra banda, el dispositiu fabricat amb TSMC 180 nm presenta una Q = 634.5 i una sensibilitat de 20.26 fA/µT · mA a 1 mbar amb V = 1 V. Finalment, s'ha dissenyat un circuit integrat que conté tots els blocs per a realitzar el condicionament de senyal del MEMS. El MEMS i l'electrònica s'han fabricat en el mateix dau amb el procés estàndard de TSMC 180 nm per tal de reduir paràsits i millorar el soroll i el consum de corrent. Les simulacions mostren una resolució de 8.23 µT /mA amb V = 1 V i BW = 10 Hz pel dispositiu dissenyat

Analysis and design of wideband voltage controlled oscillators using self-oscillating active inductors.

Voltage controlled oscillators (VCOs) are essential components of RF circuits used in transmitters and receivers as sources of carrier waves with variable frequencies. This, together with a rapid development of microelectronic circuits, led to an extensive research on integrated implementations of the oscillator circuits. One of the known approaches to oscillator design employs resonators with active inductors electronic circuits simulating the behavior of passive inductors using only transistors and capacitors. Such resonators occupy only a fraction of the silicon area necessary for a passive inductor, and thus allow to use chip area more eectively. The downsides of the active inductor approach include: power consumption and noise introduced by transistors. This thesis presents a new approach to active inductor oscillator design using selfoscillating active inductor circuits. The instability necessary to start oscillations is provided by the use of a passive RC network rather than a power consuming external circuit employed in the standard oscillator approach. As a result, total power consumption of the oscillator is improved. Although, some of the active inductors with RC circuits has been reported in the literature, there has been no attempt to utilise this technique in wideband voltage controlled oscillator design. For this reason, the dissertation presents a thorough investigation of self-oscillating active inductor circuits, providing a new set of design rules and related trade-os. This includes: a complete small signal model of the oscillator, sensitivity analysis, large signal behavior of the circuit and phase noise model. The presented theory is conrmed by extensive simulations of wideband CMOS VCO circuit for various temperatures and process variations. The obtained results prove that active inductor oscillator performance is obtained without the use of standard active compensation circuits. Finally, the concept of self-oscillating active inductor has been employed to simple and fast OOK (On-Off Keying) transmitter showing energy eciency comparable to the state of the art implementations reported in the literature

Ultra-Low Power Wake Up Receiver For Medical Implant Communications Service Transceiver

This thesis explores the specific requirements and challenges for the design of a dedicated wake-up receiver for medical implant communication services equipped with a novel “uncertain-IF†architecture combined with a high – Q filtering MEMS resonator and a free running CMOS ring oscillator as the RF LO. The receiver prototype, implements an IBM 0.18μm mixed-signal 7ML RF CMOS technology and achieves a sensitivity of -62 dBm at 404MHz while consuming \u3c100 μW from a 1 V supply

Spontaneous mechanical oscillation of a DC driven single crystal

There is a large interest to decrease the size of mechanical oscillators since this can lead to miniaturization of timing and frequency referencing devices, but also because of the potential of small mechanical oscillators as extremely sensitive sensors. Here we show that a single crystal silicon resonator structure spontaneously starts to oscillate when driven by a constant direct current (DC). The mechanical oscillation is sustained by an electrothermomechanical feedback effect in a nanobeam, which operates as a mechanical displacement amplifier. The displacement of the resonator mass is amplified, because it modulates the resistive heating power in the nanobeam via the piezoresistive effect, which results in a temperature variation that causes a thermal expansion feedback-force from the nanobeam on the resonator mass. This self-amplification effect can occur in almost any conducting material, but is particularly effective when the current density and mechanical stress are concentrated in beams of nano-scale dimensions