یک IC فرستنده ولتاژ بالا CMOS برای کاربردهای تصویربرداری پزشکی فراصوتی A CMOS High-Voltage Transmitter IC for Ultrasound Medical Imaging Applications

I. INTRODUCTION IN RECENT years, the ultrasound imaging has gained much interest in the medical field due to its less-harmful characteristic to the human body in comparison with other well-known methods such as magnetic resonance imaging, computed tomography, and X-rays. In addition, the emergence of the capacitive micromachined ultrasound transducer (CMUT) device technology [1] during the last decade has propelled the interest even further. In comparison with its piezoelectric counterpart, the CMUT provides the advantages of wider operational bandwidth, simpler fabrication for large array implementations, and more ease of integration with the front-end integrated circuits (ICs) due to compatibility with the standard CMOS process. Most recently, 2-D CMUT arrays with integrated front-end ICs have been developed for 3-D ultrasound volumetric imaging for improved benefits such as higher resolution and signal-to-noise ratio (SNR) [2]. Fig. 1 shows a typical ultrasound system block diagram for medical imaging applications. The ultrasound system consists of a transducer array, an interface transceiver comprised of a high-voltage (HV) transmitter and a low-noise receiver, and image/signal processing blocks for image construction. The analog front end of the transceiver plays a critical role in deciding the overall system performance such as the sensitivity and the SNR of the ultrasound system [3], [4]. In order to support large-size 2-D arrays, a large number of transducer elements are required, which then leads to an increase in the number of closely packed flip-chip-bonded interfacing front-end IC cells, posing significant integration issues due to the limited die area available for each cell. One of the main issues is the area-hungry HV transmitter in the interfacing analog front-end IC. The HV transmitter usually utilizes large-size HV double-diffused MOS (DMOS) transistors [2], [5], [6] to generate HV output pulse signals to drive the CMUT to produce large acoustic pressure while maintaining the reliability to prevent possible device junction breakdown. In this brief, a highly integrated HV transmitter utilizing standard CMOS transistors targeted for ultrasound medical imaging in a highly integrated needle device for obstetrics and gynecology applications is presented. Both the HV output pulse driver and the level shifter adopts the proposed multiple-stacked architecture with dynamic gate biasing circuit in order to generate over 10-Vp−p pulse signal at 1.25-MHz frequency while driving the CMUT device immersed in an oil environment. A 10-V drive voltage, which is lower than typical ultrasound applications, is chosen in this work for several reasons: 1) A CMUT device with a thin membrane and low collapse voltage is to be used for integration with the developed IC. 2) The resulting generated acoustic pressure meets the application requirements. 3) The amount of dynamic power consumption during operation has to be minimized considering tissue heating as the needle is to be inserted into the human tissue. Section II briefly addresses the transmitter architecture, while Section III describes the circuit design in detail. Section IV presents the experimental results followed by the conclusions in Section V. V. CONCLUSION A HV ultrasound transmitter IC for multiarray medical imaging applications has been implemented using the HV 0.18-μm BCD process. The HV transmitter, which includes the proposed output driver and level shifter, achieves over 10-Vp−p output pulse signal with robust reliability while only utilizing stacked standard CMOS transistors for high integration and low cost. A successful demonstration has been done for acoustic testing in an oil environment using the proposed HV transmitter IC and the developed CMUT sample. For applications requiring a higher transmitted acoustic pressure, additional stacks can be simply added to the proposed design with dynamic bias circuits to sustain a higher voltage to excite the following transducer.