Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
1999-03-19
2002-04-30
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S333000
Reexamination Certificate
active
06380766
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to ultrasound imaging for medical applications and, more particularly, to integrated circuitry including both low and high-voltage components for use with ultrasound transducer elements.
BACKGROUND OF THE INVENTION
Ultrasound imaging systems for medical applications typically employ arrays of individual ultrasound transducer elements which transmit and receive ultrasound energy. The transducer array transmits ultrasound energy into a region of interest in a patient, and receives reflected ultrasound energy, or echos, from various structures and organs within the patient's body. The imaging system then processes electronic signals generated by the elements of the transducer array, based on the received ultrasound energy, to form an image of the region of interest. The quality or resolution of the image formed is a function of the number of transmit and receive transducer elements that constitute the transducer array.
Accordingly, to achieve high image quality, a large number of transducer elements is desirable. For both two-dimensional and three-dimensional imaging applications, a preferred number of transducer elements is typically determined by a desired image resolution. The transducer elements typically are located in a hand-held transducer “head” or “handle” which is connected by a flexible cable to an electronics unit that processes the transducer signals and generates ultrasound images, as described above. Some proposed transducer heads may also include circuitry to provide transmit signals to, and process receive signals from, the individual transducer elements. Practical considerations of size, cost, and the complexity of this circuitry, as well as practical limits on the size and flexibility of the cable which carries signal conductors connecting the transducer elements to the electronics unit, pose challenges to the design of a transducer head that incorporates a large number of transducer elements for high resolution imaging applications.
In some proposed ultrasound imaging systems, the transmit circuitry that may be included in the transducer head includes high-voltage components to drive the individual ultrasound transducer elements. In some cases, low-voltage high-density digital logic circuitry to provide transmit signals to the high-voltage drivers may also be included in the transducer head. The high-voltage drivers are made from high-voltage components that are capable, for example, of operating voltages of up to approximately 100 volts. The high-voltage drivers may be fabricated as discrete components or as integrated circuits including several drivers. The low-voltage logic circuitry is fabricated as a separate integrated circuit having an operating voltage on the order of 5 volts.
In addition to transmit circuitry including the high-voltage drivers and low-voltage logic circuitry, some proposed transducer heads may include low noise, low-voltage analog receive circuitry. The low-voltage receive circuitry, like the transmit logic circuitry, typically has an operating voltage on the order of 5 volts, and may be a separate integrated circuit or may be fabricated with the low-voltage transmit logic circuitry as a monolithic integrated circuit.
As discussed above, in order to facilitate the use of a large number of transducer elements to achieve high-quality ultrasound images, it is desirable to integrate as much circuitry as possible in as small a volume as possible to reduce the size and complexity of the circuitry, whether the circuitry be located within a transducer head or in an electronics unit separate from the transducer head. In particular, if the circuitry is included in the transducer head, it is desirable to reduce the number of interconnections between any discrete integrated circuits and components within the head, as well as the number of signal conductors in the cable connecting the transducer head to the electronics unit. However, notwithstanding a reduced number of interconnections or signal conductors, the discrete high-voltage components typically employed to drive the transducer elements take up valuable space within the transducer head.
In addition, some applications, for example very high-frequency ultrasound imaging, require that transmit circuitry be located as close as possible to the transducer elements to avoid signal loading by a long cable. Accordingly, it would be advantageous to integrate high-voltage drivers for ultrasound transducer elements with either or both of the low-voltage transmit logic circuitry and the low-voltage receive circuitry as a monolithic integrated circuit.
However, high-voltage devices do not readily lend themselves to fabrication using conventional processing techniques for low-voltage integrated circuits. For example, high-voltage FETS are typically fabricated using relatively large geometry processes (10 microns) to achieve high breakdown voltages. In contrast, low-voltage integrated circuits may be fabricated using submicron geometry processes. The requirement of large junction areas for high-breakdown-voltage components is difficult to achieve using the small-geometry, high-density processing techniques employed in the fabrication of low-voltage integrated circuits. Additionally, high-voltage fabrication processes have the disadvantage that they often do not include the capability of fabricating bipolar junction transistors, which are used in many low-noise signal processing applications.
One proposed application related to actuation of mechanical devices is reported in “High voltage devices and circuits fabricated using foundry CMOS for use with electrostatic MEM actuators,” N. I. Maluf et al., Sensors and Actuators, vol. A52, pp. 187-192, 1996. In this proposal, high-voltage components and circuits for use with electrostatic micro-electromechanical (MEM) devices are fabricated using conventional processing techniques for high-density, low-voltage integrated circuits. In one example of this application, MEM actuators requiring a high-voltage drive are monolithically integrated on a single substrate with high-voltage components, using low-voltage processing techniques.
For this application, high-voltage MOS transistors are fabricated using a 2.0 micron CMOS process that includes the formation of N-well and P-base layers as lightly doped drains. High-voltage transistors fabricated in this manner are reported to have operating voltages of approximately 100 volts or less for NMOS structures, and approximately −25 volts or less for PMOS structures. However, the use of low-voltage integrated circuit processing techniques for the fabrication of high-voltage components is limited in this application to simple high-voltage differential amplifiers for driving aluminum electrostatic MEM actuator structures.
One possible approach to integrating high and low-voltage circuitry is to design and develop a custom integrated circuit fabrication line dedicated to a hybrid process. Such a hybrid process would require many masks for the various steps necessary to implement both the high and low-voltage components, and would present several optimization challenges. Moreover, designing and implementing a dedicated integrated circuit fabrication line for a custom process would be cost effective only if a large number of the custom integrated circuits are manufactured.
Another proposed solution for optimizing ultrasound imaging systems includes the design of a low-voltage transducer element by using multi-layer ceramics. Such low-voltage transducer elements eliminate the need for high-voltage transducer driver circuitry. However, as in the case of a custom integrated circuit hybrid fabrication process, the multi-layer ceramics used for low-voltage ultrasound transducer elements are costly and difficult to produce.
Accordingly, for ultrasound imaging systems and many other applications, it is desirable to integrate both high and low-voltage circuitry in a monolithically fabricated integrated circuit using readily available and reasonably cost-effective processing techni
Tra Quan
Tran Toan
Vodopia John
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