A mixed-signal multiplexing system for cable-count reduction in ultrasound probes

This paper presents an approach to time-multiplexing multiple receive signals in a miniature ultrasound probe onto a single micro-coaxial cable. The resulting reduction in the number of receive cables alleviates the design of high-element-count endoscope- or catheter-based ultrasound probes. A prototype multiplexing system is presented that employs a custom multiplexing chip that uses current-mode drivers to combine four receive channels, sampled at 25 MHz each, on a single 3-m micro-coaxial cable. On the system-side of the cable, a transimpedance amplifier turns the multiplexed signal back into a voltage, after which it is digitized and equalized to correct for channel-to-channel crosstalk due to non-idealities of the cable. The chip has been implemented in a 0.18 μm CMOS process and consumes less than 1 mW per input channel. Experimental results show that the system can successfully convey 6 MHz Gaussian-shaped pulses applied to the four input channels of the multiplexing chip to the system with a channel-to-channel crosstalk below -31 dB.