Llimos Muntal, Pere

Dette arbejde vedrører de integrerede kredsløb, der indg˚ar som en del af en bærbar ultralydsskanner. Denne type scanner er begrænset af krav til størrelse og eﬀektfor-brug. De primære udfordringer er derfor at opn˚a en acceptabel billedkvalitet indenfor de fastsatte krav. Bærbare ultralydsskannere er opbygget forskelligt fra statiske ultra-lydsskannere, da dataopsamlingen i den h˚andholdte probe er pre-beamformed, hvilket medfører en reduceret datamængde. Det komplekse databehandlingskredsløb i den h˚andholdte probe skal b˚ade være areal- og eﬀekt-eﬀektivt, kredsløbet skal samtidig opn˚a en høj ydelse indenfor de fastsatte budgetter for areal og eﬀektforbrug.En h˚andholdt probe der anvendes til bærbare ultralydsskannere indeholder adskil-lige transducere, der hver især er tilknyttet en dedikeret sender og modtager. Pre-beamformningen foreg˚ar ved at hver enkel sendekanal exciterer transduceren i en sekvens, samtidig med at modtager-kanalernes data summeres for hver excitation. Det er p˚akrævet at hver modtager-kanal b˚ade forstærker og forsinker dens signal for at opn˚a korrekt pre-beamformning. Den h˚andholdte probe indeholder analog-til-digital-konvertere (ADC), der opsamler analog data og sender disse videre i digital form til en databehandlingsen-hed.Den fysiske opbygning af ultralydstransducere gør, at det er nødvendigt at drive trans-ducerne med ﬁrkantpulser med høj spænding. Lavspændingsmodtagerne skal opn˚a et stort signal-til-støjforhold (SNR) for at kunne generere brugbare billeder. Tre inte-grerede kredsløbsprototyper er blevet fabrikeret for at sandsynliggøre anvendelsen af sende- og modtagekredsløbenes til brug i bærbare ultralydsskannere. De tre prototyper er blevet veriﬁceret eksperimentelt med tilfredsstillende resultater.Den første del af projektet er fokuseret p˚a højspændingssendekanalerne. Disse kredsløb skal generere spændingspulser op til 100 V med frekvenser omkring 5 MHz. Den første prototype chip, indeholder en fuld rekonﬁgurerbar single-ended sendekanal, der optager et chipareal p˚a 0.938 mm2 og har et eﬀektforbrug p˚a 1.41 mW. Den anden prototype chip, indeholder en fulddiﬀerentiel sendekanal, som har forbedret ydelse, optager mindre chipareal p˚a 0.18 mm2 og har et lavere eﬀektforbrug p˚a 0.936 mW sammenlignet med den første prototype.Den anden del af projektet er fokuseret p˚a modtagerkredsløbet. Den tredje prototype chip, indeholder en kontinuerttids delta-sigma analog-til-digital-konverter (CTDS ADC), der opererer med en samplingfrekvens p˚a 320 MHz, SNR p˚a 45 dB, optager et chipareal p˚a 0.0175 mm2, og har eﬀektforbrug p˚a 0.594 mW. Form˚alet med denne er at digitalis-ere modtagesignalet før pre-beamformning. SNR for ADC’en er direkte forbundet til billedkvaliteten. Forbedring af SNR er samtidig forbundet med et højere eﬀektforbrug, hvilket skaber en afvejning mellem eﬀektforbrug og billedkvalitet. Designfremgangsm˚a-den er at opn˚a det mindst mulige SNR, som fører til en acceptabel billedkvalitet med det mindst mulige eﬀektforbrug. ADC’en er implementeret som en oversamplet kon-verter med 1-bit for at simpliﬁcere den præcise digitale forsinkelse, der er nødvendig i hver modtagekanal. Ved brug af denne fremgangsm˚ade kan den digitale forsinkelse implementeres meget eﬀektivt som en digital inverter-baseret delay line, hvorved der kan opn˚as en præcis forsinkelse, der er skalerbar med procesteknologi.This work concerns the integrated circuitry contained inside a portable ultrasound scanner. These scanners are size and power limited, therefore, the main challenge is to achieve an acceptable picture quality within those restrictions. The structure of portable ultrasound scanners is diﬀerent from traditional static ultrasound scanners since the data acquired is pre-beamformed, and thereby reduced, in the handheld probe. As a result, the circuitry inside the handheld probe is complex and is required to be small and eﬃcient. Furthermore, it needs to reach enough performance to generate a usable picture quality, within the area and power budget limitations.A handheld probe for portable ultrasound scanners contains several transducers, trans-mitting channels and receiving channels. In order to pre-beamform, the transmitting channels individually excite the transducers in a sequence ﬁlling the imaging plane and the signals received from each transmit burst area summed. Each receiving channel is required to individually amplify and delay its signal in order to correctly pre-beamform. The handheld probe delivers the data to a processing unit digitally, hence, analog to digital converters (ADCs) are contained in the probe.Due to the nature of ultrasonic transducers, the transmitting circuitry needs to generate high-voltage pulses to drive them. Furthermore, the low-voltage receiving circuitry has to provide high enough signal to noise ratio (SNR) in order to generate usable imaging. For the purpose of evaluating the feasibility of the transmitting and receiving circuitry of a handheld probe for portable ultrasound scanners, three integrated circuit prototypes have been fabricated. Measurements have been performed on all of them with satisfactory results.The ﬁrst part of this project is focused on the high-voltage transmitting channels cir-cuitry. This circuitry is required to generate pulses in the range of 100 V with fre-quencies around 5 MHz. The ﬁrst prototype contains a full reconﬁgurable single-ended transmitting channel occupying a die area of 0.938 mm2 and a power consumption of 1.41 mW. The second prototype contains a full diﬀerential transmitting channel, which has improvements on performance, smaller die area of 0.18 mm2 and lower power con-sumption of 0.936 mW.The second part of the project aims at the receiving channel circuitry. The third proto-type includes a continuous-time delta-sigma analog-to-digital converter (CTDS ADC) operating at a sampling frequency of 320 MHz, a SNR of 45 dB, occupying an area of 0.0175 mm2 and a power consumption of 0.594 mW. The CTDS ADC digitizes the signal before the pre-beamform summing is applied. The SNR of the ADC is directly linked to the picture quality of the imaging. However, the SNR is also related to the power consumption, creating a tradeoﬀ between power and picture quality. The design approach will be to achieve the minimum SNR that generates an acceptable picture quality while using the minimum power possible. The ADC is implemented as an over-sampled data converter with 1-bit output in order to simplify the accurate digital delay needed in each receiving channel to pre-beamform. Using this approach, the digital delay can be very eﬃciently implemented as an inverter based digital delay line with switches, achieving accurate precise delay that scales with technology

Online Research Database In Technology

Custom Integrated Circuit Design for Portable Ultrasound Scanners

http://orbit.dtu.dk/ws/files/142083070/thesis_main.pdf

Custom Integrated Circuit Design for Portable Ultrasound Scanners

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology