2 System Overview

There is a growing interest in a handheld ultrasound systems to help maximize the effectiveness of point-of-care support and diagnosis for patients. Traditionally, ultrasound systems are of a cart-based type, which integrates a higher number of channels to achieve higher performance and excellent image quality.

Ultrasound analog front ends and transmitter chips have achieved over 80% reductions in power and size. These advancements allow for higher channel integration and the lowest power possible, which is a requirement for handheld portable probes since the probes are typically battery operated (1S, 2S). Higher receiver and transmitter channel count in the system gives a better image resolution. Figure 2-1 shows the image quality difference between a 16-channel, 32-channel, and 64-channel system. Because of the power and area limitation in portable ultrasound systems, most of systems in the market are able to integrate 16- or 32-channel receivers and transmitters. The high-voltage MUX is used to excite 128 transducer elements; see Figure 2-2. Some of the limitations for the existing design are a lower image quality because of only a 16-channel receiver and a lower frame rate because of higher imaging time due to a limited number of channels. This reference design proposes a design which contains a complete power design for TI’s high-performance, 128-channel TX, 64-channel RX ultrasound smart probe design. This reference design also can be used to power most ultrasound smart probes with a bit update.

Figure 2-1 Image Resolution and Quality Across Channel Integration

Figure 2-2 16-Channel System

To achieve the target area, all the power supplies are kept on another PCB which is vertically stacked to the RX + TX board through the connector. The other advantage of having power supplies on a separate PCB is that this arrangement increases isolation of switching noise from the power supply to sensitive receiver and transmitter devices. This power-supply board generates a total of eight different supplies (Including ±75V) from USB Type-C 5V with a capability of delivering a maximum of 15W peak power. Using TI's CDC series or LMK series clock buffer to generate synchronous clocks for the system is the usual practice. This approach leads to a higher power consumption and extra space on the board. In the proposed design, to reduce power and board space, the FPGA is used to provide clock to all the chips. The power supply board requires eight clock signals for synchronization. In ultrasound systems the transmitter is active only for 1% of imaging duration. For rest of the duration, the receiver device receives the echo to form the full image. On the same concept, the transmitter device is also kept active only for 1% duration which reduces the clock power further, the low-voltage differential signaling (LVDS) signals going to transmitter are programmed in tri-state mode for 99% duration. The LVDS buffer power in tri-state mode is 11mW/channel making the total power consumption of the clocking scheme 213mW. This is an improvement from a conventional clocking scheme power which is greater than 500mW.