Application of CTDs Conversion Technology in Medical Ultrasound System

Application of CTDs conversion technology in medical ultrasound system

So far, designers have faced the compromise of ADC selection. Pipelined converters provide high resolution and wide dynamic range, but their power consumption is quite high. Another method, discrete time Δ Σ converter hardly needs too much power, but it is strictly limited by speed. CTDs ADC continuous time Δ Sigma (CTDs) technology can fill the gap of the converter. The product recently launched by xignal company can work at 40MSample / S (equivalent to 50 60msample / s of pipelined converter), has 12 or 14 bit resolution, high functional integration (including accurate on-chip clock source), and its power consumption is only 70mW. The product also has a resistive input stage, which is easy to drive without the aid of a buffer amplifier. Figure 1 shows the relative performance comparison of CTDs ADC and pipelined converter. This figure is measured according to the FOM (performance factor) approved by IEEE. Fom is the energy measurement for each conversion. Fom also shows the future scale of the process structure, continuous time Δ Σ devices will develop along the roadmap that gives a higher performance level.

Figure 2 shows a complete a / D conversion system. The figure on the left shows a complete system. Five external circuit elements are required for pipelined converters. They are programmable gain amplifiers (gain control through separate DA); Anti aliasing filter for removing noise; An input driver that buffers the capacitive input of the ADC itself; High performance clock and PLL with accurate timing reference. In contrast, continuous time Δ Σ implementation method removes the required anti aliasing filter and input driver, while xignal implementation method integrates all other functions on chip.

The advantages of CTDs conversion technology are: faster and simpler system design, lower power consumption, and no trade-off between dynamic range and speed. In multi-channel applications, the above advantages of CTDC ADC can add value, and enable designers to adopt new and beneficial system structure, which was impossible before. This technology has a wide range of applications, including all fields of the electronic industry, especially in the field where analog signals from various sensors need to be converted into digital signals. Medical ultrasound is used in medical ultrasound system. The ultrasonic transducer emits ultrasonic, which is reflected by the target and received by the transducer again. In order to scan a large area and gather on the target at a certain distance, the target needs to be small, and multiple transmitting / receiving elements need to be configured in one-dimensional or two-dimensional array to form a beam. The focusing and direction of the beam can be controlled electronically. The transducer is connected to the data processing unit that processes data through flexible cables. Each energy conversion element is connected to the processing unit through its own data channel or multiplexing circuit. The allocation of high-end system is up to 512 channels, that of medium performance system is up to 256 channels, and that of portable system is up to 128 channels. According to the distance from the target to the sensor head and the nature of the target, the amplitude of the analog signal received and transmitted through the cable is wide. Therefore, the cable is composed of several low loss coaxial cores, which is one of the expensive components of the ultrasonic system. Nevertheless, cable loss and loss on the transducer interface are requirements for high-performance and quite expensive receivers. Signal integrity if the ADC is made close to the transducer, the signal integrity will be improved. The integration of analog front-end with ADC and placing the device directly in the transducer will reduce the requirements for receiver performance, and digital transmission is more reliable and lower cost than analog signal processing unit. However, for the analog front-end used before the development of CDTs technology, its pipelined ADC consumes up to 0.5W per channel. For a medium-sized system (128 channels), its power consumption is up to 64W, and the generated heat will affect the performance of the transducer head and cause great discomfort to patients and doctors. On the contrary, in the same system, the power consumption of CTDs scheme is only 8.75w, or even less (multi-channel ADC devices are used to share some resources, such as PLL bridging multi-channel). One 8-channel 12 bit ADC can achieve power consumption of 40mW / channel or 128 channels, and power consumption of 5.12w. Portable systems require reducing the size of ultrasonic scanners. In the implementation of small and low-cost systems, ADC power consumption is an important design parameter. This small system conversion occurs in the transducer head or processing unit, and the system requires the least cooling. The new system may also be battery powered, so minimizing power consumption is a more critical factor. Continue to study. People study the use of digital beamformer instead of analog beamformer in continuous wave Doppler applications, and process all data from several ultrasonic nodes through the same digital processing path. The increased power consumption in the digital domain can be reduced by using advanced CMOS technology with lower power supply voltage of 1.2V or lower. With such a low voltage, the general ADC technology cannot achieve the required performance. Continuous time Δ Σ technology with 1.2V power supply can provide the required performance, and will further reduce power consumption and size with the development of CMOS technology. The simplified structure of the ultrasonic system using CTDs ADC in the transducer head is shown in Fig. 3. In addition to the ADC, the active transducer includes a low-power variable gain amplifier, a serializer and a digital interface, which can greatly reduce the number of cables used to interconnect the main processing unit.

The advantage of CDTs ADC is to provide the required high speed and high resolution at the lowest possible power consumption. In sensor related applications of automotive, medical, industrial and test and measurement equipment, this technology can be used to form a new structure to make a / D conversion close to the sensor.

Application of CTDs Conversion Technology in Medical Ultrasound System 1

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