The work done in this thesis involves the design of a Front End for MEMS ultrasonic transducers for medical purposes as part of the DENECOR project. The transducer is a CMUT (Capacitive Micromachined Ultrasound Transducer): in transmission mode the voltage across the MEMS is varied, producing a vibration of the membrane constituting the top electrode of the capacitor; in receiving mode the acoustic wave impinging on the sensor membrane causes a change in its capacitance. The Front End consists of a pulser, a receiving chain and a T/R switch. The pulser is high voltage, as the CMUT needs to be driven at 200 Volts; the slope of its output signal can be programmed by enabling or disabling additional current generators. The receiving chain includes a capacitive feedback LNA and an operational amplifier configured as buffer. The gain of the LNA is made programmable by changing the value of the feedback capacitor. The buffer is a two stage class AB amplifier. To protect the low-voltage LNA during transmission, the latter is isolated from the high-voltage pulser by means of a T/R switch, optimized for low on-state resistance and high off-state isolation. Noise simulations have been carried out to make sure the total receiving system noise stays below that of the CMUT sensor for any LNA gain setting. Also the linearity performances have been checked for any possible gain value. The whole circuit has been fabricated in BCDSOI technology, providing Bipolar, MOSFET and DMOS transistors on Silicon on Insulator wafers.
Front End per Trasduttori Capacitivi MEMS ad Ultrasuoni in Tecnologia BCD SOI. Il lavoro svolto in questa tesi riguarda il progetto di un Front End per trasduttori MEMS ad ultrasuoni a scopo medicale nell'ambito del progetto DENECOR. Il trasduttore è un CMUT (Capacitive Micromachined Ultrasound Transducer): in trasmissione la tensione ai capi del MEMS viene variata e produce una vibrazione della membrana che costituisce l’elettrodo superiore; in ricezione l’onda acustica che urta la membrana del sensore provoca una variazione della sua capacità. Il Front End consiste in un pulser, una catena di ricezione e un T/R switch. Il pulser lavora ad alta tensione poiché il CMUT deve essere pilotato a 200 Volt; la pendenza del segnale di uscita può essere impostata abilitando o disabilitando dei generatori di corrente. La catena di ricezione comprende un LNA a feedback capacitivo e un amplificatore operazionale connesso a buffer. Il guadagno dell’LNA può essere modificato cambiando il valore della capacità di feedback. Il buffer è un amplificatore in classe AB a 2 stadi. Per proteggere l'LNA durante la trasmissione, quest'ultimo viene isolato dal pulser ad alta tensione tramite un T/R switch, ottimizzato per avere bassa resistenza in on-state ed elevato isolamento in off-state. Sono state effettuate simulazioni di rumore per assicurarsi che il rumore introdotto dall’intera catena di ricezione restasse più basso di quello introdotto dal sensore per qualsiasi valore di guadagno dell’LNA. Anche le performance in termini di linearità sono state analizzate per ogni valore di guadagno. Il circuito è stato fabbricato in tecnologia BCDSOI, che include transistor bipolari, MOSFET e DMOS su wafer di Silicon on Insulator.
Front End for MEMS Ultrasonic Capacitive Transducers in BCDSOI Technology.
ELGANI, ALESSIA MARIA
2014/2015
Abstract
The work done in this thesis involves the design of a Front End for MEMS ultrasonic transducers for medical purposes as part of the DENECOR project. The transducer is a CMUT (Capacitive Micromachined Ultrasound Transducer): in transmission mode the voltage across the MEMS is varied, producing a vibration of the membrane constituting the top electrode of the capacitor; in receiving mode the acoustic wave impinging on the sensor membrane causes a change in its capacitance. The Front End consists of a pulser, a receiving chain and a T/R switch. The pulser is high voltage, as the CMUT needs to be driven at 200 Volts; the slope of its output signal can be programmed by enabling or disabling additional current generators. The receiving chain includes a capacitive feedback LNA and an operational amplifier configured as buffer. The gain of the LNA is made programmable by changing the value of the feedback capacitor. The buffer is a two stage class AB amplifier. To protect the low-voltage LNA during transmission, the latter is isolated from the high-voltage pulser by means of a T/R switch, optimized for low on-state resistance and high off-state isolation. Noise simulations have been carried out to make sure the total receiving system noise stays below that of the CMUT sensor for any LNA gain setting. Also the linearity performances have been checked for any possible gain value. The whole circuit has been fabricated in BCDSOI technology, providing Bipolar, MOSFET and DMOS transistors on Silicon on Insulator wafers.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/22223