Implementation of a VLSI amplifier interfaced with biomedical sensors for ultra wide band data transmission

This thesis presents a CMOS Amplifier with High Common Mode rejection designed in UMC 130nm technology. The goal is to achieve a high amplification factor for a wide range of biological signals (with frequencies in the range of 10Hz-1KHz) and to reject the common-mode noise signal. It is here presented a Data Acquisition System, composed of a Delta-Sigma-like Modulator and an antenna, that is the core of a portable low-complexity radio system; the amplifier is designed in order to interface the data acquisition system with a sensor that acquires the electrical signal. The Modulator asynchronously acquires and samples human muscle activity, by sending a Quasi-Digital pattern that encodes the acquired signal. There is only a minor loss of information translating the muscle activity using this pattern, compared to an encoding technique which uses astandard digital signal via Impulse-Radio Ultra-Wide Band (IR-UWB). The biological signals, needed for Electromyographic analysis, have an amplitude of 10-100μV and need to be highly amplified and separated from the overwhelming 50mV common mode noise signal. Various tests of the firmness of the concept are presented, as well the proof that the design works even with different sensors, such as Radiation measurement for Dosimetry studies.

Caratterizzazione e generazione di segnali PWM per amplificatori in classe D ad alta efficienza

The convergence of information technology and consumer electronics towards battery powered portable devices has increased the interest in high efficiency, low dissipation amplifiers. Class D amplifiers are the state of the art in low power consumption and high performance amplification. In this thesis we explore the possibility of exploiting nonlinearities introduced by the PWM modulation, by designing an optimized modulation law which scales its carrier frequency adaptively with the input signal's average power while preserving the SNR, thus reducing power consumption. This is achieved by means of a novel analytical model of the PWM output spectrum, which shows how interfering harmonics and their bandwidth affect the spectrum. This allows for frequency scaling with negligible aliasing between the baseband spectrum and its harmonics. We performed low noise power spectrum measurements on PWM modulations generated by comparing variable bandwidth, random test signals with a variable frequency triangular wave carrier. The experimental results show that power-optimized frequency scaling is both feasible and effective. The new analytical model also suggests a new PWM architecture that can be applied to digitally encoded input signals which are predistorted and compared with a cosine carrier, which is accurately synthesized by a digital oscillator. This approach has been simulated in a realistic noisy model and tested in our measurement setup. A zero crossing search on the obtained PWM modulation law proves that this approach yields an equivalent signal quality with respect to traditional PWM schemes, while entailing the use of signals whose bandwidth is remarkably smaller due to the use of a cosine instead of a triangular carrier.

Studio dei circuiti di clamper negli amplificatori operanti in classe e

Questa tesi tratta dell’amplificatore di potenza (PA–Power Amplifier) operante in classe E. Si tratta di un convertitore DC/AC ad elevato rendimento che può trovare impiego in numerose applicazioni in cui il problema della generazione di calore o la necessità di non sprecare energia sono particolarmente stringenti (ad esempio apparati per cui non è previsto un impianto di raffreddamento e/o apparati alimentati a batteria). L’elevato rendimento di un amplificatore operante in classe E deriva dalle specifiche forme d’onda ai capi del dispositivo attivo impiegato, tali per cui la perdita di commutazione durante la fase di accensione dello switch diviene pressoché trascurabile (Zero-Voltage-Switching e Zero-Derivative-Voltage Turn-ON). Il prezzo da pagare per ottenere queste benefiche forme d’onda è quello di avere un valore di cresta della tensione sul dispositivo che commuta assai più elevato del valore medio, coincidente con la tensione di alimentazione DC. In generale si stima una tensione di picco fra le 3 e le 5 volte più elevata della tensione DC, in funzione del Duty-Cycle e dell’assorbimento di corrente sul carico. Occorre poi tenere presente che in condizioni dinamiche (ad esempio qualora si collegasse direttamente l’amplificatore all’alimentazione) potrebbero innescarsi dei transitori tali per cui la tensione di picco ecceda anche il range suddetto. Per questo motivo è bene porre un limite alla massima tensione di picco adottando dei circuiti di protezione del transistore al fine di evitare la sua distruzione per limiti legati alla tensione di breakdown. Questi circuiti sono denominati clamper: in questa tesi valuteremo le modalità con cui si può implementare tale protezione; valuteremo, inoltre, i vantaggi e gli svantaggi derivanti dall’impiego di tali circuiti. Questi clamper sono prevalentemente di tipo dissipativo (Zener); nel corso della tesi si è studiato la realizzazione di un clamper rigenerativo che utilizza un trasformatore, ma si è constatata la irrealizzabilità fisica a causa della inevitabile presenza della induttanza dispersa.

Implementazione su fpga di un pre-distorsore digitale a banda larga per sistemi a microonde di backhaul

The development of next generation microwave technology for backhauling systems is driven by an increasing capacity demand. In order to provide higher data rates and throughputs over a point-to-point link, a cost-effective performance improvement is enabled by an enhanced energy-efficiency of the transmit power amplification stage, whereas a combination of spectrally efficient modulation formats and wider bandwidths is supported by amplifiers that fulfil strict constraints in terms of linearity. An optimal trade-off between these conflicting requirements can be achieved by resorting to flexible digital signal processing techniques at baseband. In such a scenario, the adaptive digital pre-distortion is a well-known linearization method, that comes up to be a potentially widely-used solution since it can be easily integrated into base stations. Its operation can effectively compensate for the inter-modulation distortion introduced by the power amplifier, keeping up with the frequency-dependent time-varying behaviour of the relative nonlinear characteristic. In particular, the impact of the memory effects become more relevant and their equalisation become more challenging as the input discrete signal feature a wider bandwidth and a faster envelope to pre-distort. This thesis project involves the research, design and simulation a pre-distorter implementation at RTL based on a novel polyphase architecture, which makes it capable of operating over very wideband signals at a sampling rate that complies with the actual available clock speed of current digital devices. The motivation behind this structure is to carry out a feasible pre-distortion for the multi-band spectrally efficient complex signals carrying multiple channels that are going to be transmitted in near future high capacity and reliability microwave backhaul links.

Modelling, simulation and characterization of epithelial cell culture biochip

A microfluidic Organ-on-Chip has been developed for monitoring the epithelial cells monolayer. Equivalent circuit Model was used to determine the electrical properties from the impedance spectra of the epithelial cells monolayer. Black platinum on platinum electrodes was electrochemically deposited onto the surface of electrodes to reduce the influence of the electrical double layer on the impedance measurements. Measurements of impedance with an Impedance Analyzer were done to validate the equivalent circuit model and the decrease of the double layer effect. A Lock-in Amplifier was designed to measure the impedance.