A design solution for TI portable ultrasound system

Block diagram (SBD) of a portable ultrasound machine that uses TI's TMS320 series processors to perform beamforming, pre-processing, and back-end processing tasks, and interfaces to TI's analog front end, pulse generator, and output DACs.

Design Considerations

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Similar to fixed ultrasound systems, portable ultrasound systems use array receivers to construct images through time shifting, scaling, and intelligent summing of echo energies. However, the challenge in developing portable systems is to maintain acceptable image quality while meeting portable size and runtime requirements. This is usually achieved by reducing the number of channels used in the device, trading off image quality vs. information, thereby reducing power consumption and size.

The concept of time translation and zoom (based on the signal received by the sensor array) provides the ability to "focus" on a single point in the scan area. By focusing on different points in a certain order, the image is finally collected. Using more integrated solutions can help improve signal integrity and reliability. A typical example is the use of high-voltage pulse generators that integrate DACs, low-pass filters, and amplifiers, thereby simplifying filtering requirements and reducing noise in the transmit signal chain. Similarly, the use of a complete integrated analog portable ultrasound receive front end can reduce noise and the number of components (they provide support for the channels used in the design).

Since the output is graphical in nature, using a touchscreen as an interface allows for a large screen display while maximizing the use of space, ensuring a smaller form factor. Using multiple TI DSPs, such as the C64XX coupled with the OMAP35XX, allows for a fully integrated backend. In addition to having powerful cores for video acceleration of graphics displays, the Cortex A8 processor can help manage the OS and touchscreen interface to reduce power consumption by powering down processors that are not active and eliminating other subsystems. To compensate for the reduction in the number of channels, the image can be post-processed by delaying the image display and collecting more data that needs to be presented. This produces a more accurate image while balancing the ability to view the image in real time with the power consumption of the processor.

Power and battery management are key factors in this system, and the main design considerations include ultra-low power consumption and high efficiency driven by the need to extend battery life, as well as high accuracy. Other requirements may drive the need to record images, wired or wireless interfaces for transmitting images. In addition, features such as touch screen control and display backlighting are critical to the application of this device for ease of use. Adding all these features without significantly increasing power consumption has become a huge challenge. For medical equipment, it is critical to be able to monitor the remaining power in the device. Texas Instruments' (TI) processors, instrumentation and buffer amplifiers, power and battery management (such as Impedance Track fuel gauges), audio codecs, and wired and wireless interface device portfolio provide an ideal tool box for this system.