Smallest 128ch Multiplexer Design for Ultrasound Using 4 of TMUX9832 vs 2 of 64 Channel Devices

Abstract

Ultrasound systems use piezo-electric transducer elements to generate ultrasound beams that are used for imaging. Modern day ultrasound systems have 128-512 piezo-electric transducers arranged in an array, which are excited to high voltage (up to ±100V). This can call for an equal number of transmitters and receiver modules to be added to the system. This can be costly and can lead to an increased design size. To overcome this, often high-voltage multiplexers are used to reduce the number of transmitters and receiver modules. Since each channel needs independent control, the number of HV switches needed in the system can go as high as 512. With such a high number of switches, the area occupied by switches in the system becomes critical, especially in ultrasound probes and hand-held systems which are compact in size. This application note focuses on TI’s 32 channel HV switch design, TMUX9832, which is the smallest in the market with a unique pinout that simplifies board layout . This document highlights on how using 4 x TMUX9832 is still simpler compared to 2 x 64 channel competitor devices.

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1 Introduction

As the imaging technology is improving in ultrasound systems, there has been an increasing demand to fit more transducer elements along with HV switches in ultrasound probes, while keeping the same form factor. This need has driven to develop switches with high channel density which can be laid out compactly on the PCB with minimal effort.

To understand the use case better, look at how HV multiplexers and switches fit into a present-day ultrasound system. In this context, the multiplexer is responsible for connecting the transmit and receive circuitry to the transducers. The channels of the multiplexer are activated in turn to drive sequential sections of the probe elements. Each multiplexer channel passes the transmitter’s ±100V pulses to each piezoelectric element. When an element subsequently receives the return signal from the subject of imaging, the multiplexer also passes this signal back to the receiver circuitry for amplification, digital conversion, processing, and display.

Figure 1-1 Typical Block Diagram for 128 Channel Ultrasound System

For this application, TI recommends the TMUX9832 device, which is the latest beyond the supply 1:1 32 channel switch.