Analog Front-end Design for Wearable Ultrasound Systems

  • Authors: K. Chen, B. Lam, S. Lee, H.-S. Lee, A. P. Chandrakasan, C. G. Sodini
  • Sponsorship: CICS

The capacitive micromachined ultrasound transducer (CMUT) is an alternative to traditional piezoelectric transducers. The CMUT technology provides an opportunity for highly integrated ultrasound-imaging system solutions because of its CMOS compatibility and ease of large array fabrication[1].

This project aims to provide a highly flexible platform for 3D ultrasound imaging. Figure 1 presents the system architecture. The CMUT device is flip-chip bonded to the supporting electronic circuits, which eliminates the cables. As a result, the channel count of the imaging system is increased, and the capacitive loading due to cables is greatly reduced. The transmitters in the system are reconfigurable to implement Tx beamforming; the analog front-end receivers[2] and the DSP perform various Rx beamforming algorithms from the received echo waveforms[3].

We fabricated a 2D ASIC in 0.18µm HV CMOS process, which includes 16×16 channels of Tx and Rx analog front-end circuits. An LNA and a Tx/Rx HV switch are placed under each CMUT element to maintain signal quality, with the layout matched to each CMUT element area. In contrast, the pulsing transmitters and the VGAs are placed on the sides, so that the hardware can be shared. The architecture is designed to be flexible enough to ensure beam-steering and beam-focusing in 3D space. Meanwhile, the active channel count and power dissipation are reduced. The ASIC-CMUT assembly is realized using a PCB interposer and the flip-chip bonding technology (shown in Figure 2). Characterization of the system is being performed.

  1. O. Oralkan, “Acoustical Imaging Using Capacitive Micromachined Ultrasonic Transducer Arrays: Devices, Circuits, and Systems,” Ph.D. thesis, Stanford, Palo Alto, 2004. [↩]
  2. K. Chen, A. Chandrakasan, and C. Sodini, “Ultrasonic Imaging Front-End Design for CMUT: A 3-Level 30Vpp Pulse-Shaping Pulser with Improved Efficiency and a Noise-Optimized Receiver,” Asian Solid-State Circuits Conference, IEEE., Nov. 2012. [↩]
  3. K. Chen, B. Lam, C. Sodini, and A. Chandrakasan, “System Energy Model for a Digital Ultrasound Beamformer with Image Quality Control,” IEEE Ultrasonics Symposium, Oct. 2012. [↩]

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