This article presents a 4096-element ultrasound probe for high volume-rate (HVR) cardiovascular imaging. The probe consists of two application-specific integrated circuits (ASICs), each of which interfaces with a 2048-element monolithically-integrated capacitive micro-machined ultrasound transducer (CMUT) array. The probe can image a 60° × 60° × 10-cm volume at 2000 volumes/s, the highest volume-rate with in-probe channel-count reduction reported to date. It uses 2 × 2 delay-and-sum micro-beamforming (μBF) and 2× time-division multiplexing (TDM) to achieve an 8× receive (RX) channel-count reduction. Equalization, trained using a pseudorandom bit-sequence generated on the chip, reduces TDM-induced crosstalk by 10 dB, enabling power-efficient scaling of the cable drivers. The ASICs also implement a novel transmit (TX) beamformer (BF) that operates as a programmable digital pipeline, which enables steering of arbitrary pulse-density modulated (PDM) waveforms. The TX BF drives element-level 65 V unipolar pulsers, which in turn drive the CMUT array. Both the TX BF and RX μBF are programmed with shift-registers (SRs) that can either be programmed in a row-column fashion for fast upload times, or daisy-chain fashion for a higher flexibility. The layout of the ASICs is matched to the 365-μm-pitch monolithically-integrated CMUT array. While operating, the RX and logic power consumption per element is 0.85 and 0.10 mW, respectively. TX power consumption is highly waveform dependent, but is nominally 0.34 mW. Compared to the prior art, the probe has the highest volume rate, and features among the largest imaging arrays (both in terms of element-count and aperture) with a high flexibility in defining the TX waveform. These properties make it a suitable option for applications requiring HVR imaging of a large region of interest.

This article presents an application-specific integrated circuit (ASIC) for catheter-based 3-D ultrasound imaging probes. The pitch-matched design implements a comprehensive architecture with high-voltage (HV) transmitters, analog front ends, hybrid beamforming analog-To-digital converters (ADCs), and data transmission to the imaging system. To reduce the number of cables in the catheter while maintaining a small footprint per element, transmission (TX) beamforming is realized on the chip with a combination of a shift register (SR) and a row/column (R/C) approach. To explore an additional cable-count reduction in the receiver part of the design, a channel with a combination of time-division multiplexing (TDM), subarray beamforming, and multi-level pulse amplitude modulation (PAM) data transmission is also included. This achieves an 18-fold cable-count reduction and minimizes the power consumption in the catheter by a load modulation (LM) cable driver. It is further explored how common-mode interference can limit beamforming gain and a strategy to reduce its impact with local regulators is discussed. The chip was fabricated in TSMC 0.18-m HV BCD technology and a 2-D PZT transducer matrix of 16 × 18 elements with a pitch of 160 m and a center frequency of 6 MHz was manufactured on the chip. The system can generate all required TX patterns at up to 30 V, provides quick settling after the TX phase, and has an reception (RX) power consumption of only 1.12 mW/element. The functionality and operation of up to 1000 volumes/s have been demonstrated in electrical and acoustic imaging experiments.

This article presents an application-specific integrated circuit (ASIC) for battery-powered ultrasound (US) devices. The ASIC implements a novel energy-efficient high-voltage (HV) pulser that generates HV transmit (TX) pulses directly from a low-voltage (LV) battery supply. By means of a single off-chip inductor, energy is supplied to a US transducer in a resonant fashion, directly generating half-period sinusoidal HV pulses on the transducer, while consuming substantially less energy than a conventional class-D pulser. By recycling residual reactive energy from the transducer back to the input, the energy consumption is further reduced by more than 50%. The autocalibration techniques are leveraged to deal with tolerances of the inductor, transducer, and battery supply and thus maximize the energy efficiency. A prototype chip was fabricated in TSMC 0.18-μm HV BCD technology and used to drive external 120-pF capacitive micromachined US transducers (CMUTs) with a center frequency of approximately 2.5 MHz. Electrical measurements show that the prototype can generate pulses with a peak amplitude between 10 and 30 V accurate to within ±1 V. Acoustic measurements demonstrate successful ultrasonic pulse transmission and pulse-echo measurements. The prototype reaches a peak efficiency of 0.23 fCV ² , which is the highest reported to date for HV pulsers targeting US imaging.

Objective: Described here is the development of an ultrasound matrix transducer prototype for high-frame-rate 3-D intra-cardiac echocardiography. Methods: The matrix array consists of 16 × 18 lead zirconate titanate elements with a pitch of 160 µm × 160 µm built on top of an application-specific integrated circuit that generates transmission signals and digitizes the received signals. To reduce the number of cables in the catheter to a feasible number, we implement subarray beamforming and digitization in receive and use a combination of time-division multiplexing and pulse amplitude modulation data transmission, achieving an 18-fold reduction. The proposed imaging scheme employs seven fan-shaped diverging transmit beams operating at a pulse repetition frequency of 7.7 kHz to obtain a high frame rate. The performance of the prototype is characterized, and its functionality is fully verified. Results: The transducer exhibits a transmit efficiency of 28 Pa/V at 5 cm per element and a bandwidth of 60% in transmission. In receive, a dynamic range of 80 dB is measured with a minimum detectable pressure of 10 Pa per element. The element yield of the prototype is 98%, indicating the efficacy of the manufacturing process. The transducer is capable of imaging at a frame rate of up to 1000 volumes/s and is intended to cover a volume of 70° × 70° × 10 cm. Conclusion: These advanced imaging capabilities have the potential to support complex interventional procedures and enable full-volumetric flow, tissue, and electromechanical wave tracking in the heart.

This article presents a pitch-matched transceiver application-specific integrated circuit (ASIC) for a wearable ultrasound device intended for transfontanelle ultrasonography, which includes element-level 20-V unipolar pulsers with transmit (TX) beamforming, and receive (RX) circuitry that combines eightfold multiplexing, four-channel micro-beamforming (?BF), and subgroup-level digitization to achieve an initial 32-fold channel-count reduction. The ?BF is based on passive boxcar integration, merged with a 10-bit 40 MS/s SAR ADC in the charge domain, thus obviating the need for explicit anti-alias filtering (AAF) and power-hungry ADC drivers. A compact and low-power reference generator employs an area-efficient MOS capacitor as a reservoir to quickly set a reference for the ADC in the charge domain. A low-power multi-level data link, based on 16-level pulse-amplitude modulation, concatenates the outputs of four ADCs, providing an overall 128-fold channel-count reduction. A prototype transceiver ASIC was fabricated in a 180-nm BCD technology, and interfaces with a 2-D PZT transducer array of 16 × 16 elements with a pitch of 125 ?m and a center frequency of 9 MHz. The ASIC consumes 1.83 mW/element. The data link achieves an aggregate 3.84 Gb/s data rate with 3.3 pJ/bit energy efficiency. The ASIC's functionality has been demonstrated through electrical, acoustic, and imaging experiments.

While medical imaging using ultrasound is an established field, technical advances are enabling a range of new-use cases and associated new ultrasound imaging devices. Examples include catheters capable of providing real-time 3D images to guide minimally invasive interventions and wearable devices for new monitoring and diagnostic applications. In contrast with conventional probes, which contain little or no electronics, these new devices need to become “smart”: integrated circuits need to be integrated into the probe to interface in a pitch-matched fashion with the many transducer elements (typically 1000+) needed for real-time 3D imaging. This chapter discusses the challenges associated with the design of such pitch-matched integrated circuits, focusing on strategies for channel-count reduction, beamforming, and digitization. The chapter includes a case study of a state-of-the-art catheter-based design for high-frame-rate 3D intracardiac imaging.

This article presents a low-power and small-area transceiver application-specific integrated circuit (ASIC) for 3-D trans-fontanelle ultrasonography. A novel micro-beamforming receiver architecture that employs current-mode summation and boxcar integration is used to realize delay-and-sum on an N -element sub-array using N× fewer capacitive memory elements than conventional micro-beamforming implementations, thus reducing the hardware overhead associated with the memory elements. The boxcar integration also obviates the need for explicit anti-aliasing filtering in the analog front end, thus further reducing die area. These features facilitate the use of micro-beamforming in smaller pitch applications, as demonstrated by a prototype transceiver ASIC employing micro-beamforming on sub-arrays of N=4 elements, targeting a wearable ultrasound device that monitors brain perfusion in preterm infants via the fontanel. To meet its strict spatial resolution requirements, a 10-MHz 100- μ m-pitch piezoelectric transducer array is employed, leading to a per-element die area > 2 × smaller than prior designs employing micro-beamforming.

In traditional 2-D ultrasound probes, a 1-D transducer array is directly connected to an imaging system. With the introduction of 3-D probes that have 2-D arrays with thousands of elements, this approach has become impractical. Ultrasound ASICs can enable this transition by shifting part of the system functionality into the probe to reduce interconnect and cost. On-chip implementation of the analog-to-digital converter (ADC) has recently been shown to be particularly beneficial but comes with a significant power and area penalty. Current ultrasound converters are commonly implemented as successive approximation register (SAR) ADCs and designed following general-purpose design methodologies. In this work, the impact of SAR ADC non-idealities on postprocessed images is studied to achieve better trade-offs between performance and cost for ultrasound imaging.

High frame rate 3D intracardiac echography (3D-ICE) might enable full-volumetric flow, tissue, and electro-mechanical wave tracking in the heart, thus supporting complex interventional procedures. Designing ICE transducers is very challenging due to the constraints imposed by the catheter's diameter on the transducer aperture and cable accommodation within the shaft. Current ICE probes only offer a 2D or limited 3D field of view at low frame rates. This work presents the design, fabrication, and characterization of an ICE prototype transducer aiming at high frame rate 3D imaging with a large field of view.

This paper presents a pitch-matched transceiver ASIC integrated with a 2-D transducer array for a wearable ultrasound device for transfontanelle ultrasonography. The ASIC combines 8-fold multiplexing, 4-channel micro-beamforming (μ BF) and sub-array-level digitization to achieve a 128-fold channel-count reduction. The μ BF is based on passive boxcar integration and interfaces with a 10-bit 40 MS/s SAR ADC in the charge domain, thus obviating the need for explicit anti-alias filtering and power-hungry ADC drivers. A compact and low-power reference generator employs an area-efficient MOS capacitor as a reservoir to quickly set a reference for the ADC in the charge domain. A low-power multi-level data link concatenates outputs of four ADCs, leading to an aggregate 3.84 Gb/s data rate. Per channel, the RX circuit consumes 2.06 mW and occupies 0.05 mm2.

In this letter, a compact high-voltage (HV) transmit circuit for dense 2-D transducer arrays used in 3-D ultrasonic imaging systems is presented. Stringent area requirements are addressed by a unipolar pulser with embedded transmit/receive switch. Combined with a capacitive HV level shifter, it forms the ultrasonic HV transmit circuit with the lowest reported HV transistor count and area without any static power consumption. The balanced latched-based level shifter implementation makes the design insensitive to transients on the HV supply caused by pulsing, facilitating application in probes with limited local supply decoupling, such as imaging catheters. Favorable scaling through resource sharing benefits massively arrayed architectures while preserving full individual functionality. A prototype of 8 × 9 elements was fabricated in the TSMC 0.18 μm HV BCD technology and a 160μm×160μm PZT transducer matrix is manufactured on the chip. The system is designed to drive 65-V peak-to-peak pulses on 2-pF transducer capacitance and hardware sharing of six elements allows for an area of only 0.008 mm2 per element. Electrical characterization as well as acoustic results obtained with the 6-MHz central frequency transducer are demonstrated.

In this article, an application-specific integrated circuit (ASIC) for 3-D, high-frame-rate ultrasound imaging probes is presented. The design is the first to combine element-level, high-voltage (HV) transmitters and analog front-ends, subarray beamforming, and in-probe digitization in a scalable fashion for catheter-based probes. The integration challenge is met by a hybrid analog-to-digital converter (ADC), combining an efficient charge-sharing successive approximation register (SAR) first stage and a compact single-slope (SS) second stage. Application in large ultrasound imaging arrays is facilitated by directly interfacing the ADC with a charge-domain subarray beamformer, locally calibrating interstage gain errors and generating the SAR reference using a power-efficient local reference generator. Additional hardware-sharing between neighboring channels ultimately leads to the lowest reported area and power consumption across miniature ultrasound probe ADCs. A pitch-matched design is further enabled by an efficient split between the core circuitry and a periphery block, the latter including a datalink performing clock data recovery (CDR) and time-division multiplexing (TDM), which leads to a 12-fold total channel count reduction. A prototype of $8{\times }9$ elements was fabricated in a TSMC 0.18- $\mu \text{m}$ HV BCD technology and a 2-D PZT transducer matrix with a pitch of $160 \mu \text{m}$ , and a center frequency of 6 MHz was manufactured on the chip. The imaging device operates at up to 1000 volumes/s, generates 65-V transmit pulses, and has a receive power consumption of only 1.23 mW/element. The functionality has been demonstrated electrically as well as in acoustic and imaging experiments.

Clamp-on ultrasonic flow meters (UFMs) are installed on the outside of the pipe wall. Typically, they consist of two single-element transducers mounted on angled wedges, which are acoustically coupled to the pipe wall. Before flow metering, the transducers are placed at the correct axial position by manually moving one transducer along the pipe wall until the maximum amplitude of the relevant acoustic pulse is obtained. This process is time-consuming and operator-dependent. Next to this, at least five parameters of the pipe and the liquid need to be provided manually to compute the flow speed. In this work, a method is proposed to obtain the five parameters of the pipe and the liquid required to compute the flow speed. The method consists of obtaining the optimal angles for different wave travel paths by varying the steering angle of the emitted acoustic beam systematically. Based on these optimal angles, a system of equations is built and solved to extract the desired parameters. The proposed method was tested experimentally with a custom-made clamp-on UFM consisting of two linear arrays placed on a water-filled stainless steel pipe. The obtained parameters of the pipe and the liquid correspond very well with the expected (nominal) values. Furthermore, the performed experiment also demonstrates that a clamp-on UFM based on transducer arrays can achieve self-alignment without the need to manually move the transducers

Intra-cardiac echography (ICE) probes (Fig. 32.2.1) are widely used in electrophysiology for their good procedure guidance and relatively safe application. ASICs are increasingly employed in these miniature probes to enhance signal quality and reduce the number of connections needed in mm-diameter catheters [1]-[5]. 3D visualization in real-time is additionally enabled by 2D transducer arrays with, for each transducer element, a high-voltage (HV) transmit (TX) part, to generate acoustic pulses of sufficient pressure, and a receive (RX) path, to process the resulting echoes. To achieve the required reduction in RX channels, micro-beamforming (BF), which merges the signals from a subarray using a delay-and-sum operation, has been shown to be an effective solution [3], [4]. However, due to the frame-rate reduction that is associated with BF, these designs cannot serve emerging high-frame-rate imaging modes (1000 volumes/s) like 3D blood-flow and elastography imaging. In-probe digitization has recently been investigated to provide further channel-count reduction, make data transmission more robust, and enable pre-processing in the probe [1]-[3]. However, these earlier designs have either no TX functionality [2], [3] or only low-voltage (LV) TX [1] integrated. Combining BF and digitization with area-hungry HV transmitters in a pitch-matched scalable fashion while supporting high-frame-rate imaging remains an unmet challenge. The work presented in this paper meets this target, enabled by a hybrid ADC, the small die size of which allows for co-integration with 65V element-level pulsers.

Over the past decades, ultrasound imaging has made considerable progress based on the advancement of imaging systems as well as transducer technology. With the need for advanced transducer arrays with complex designs and technical requirements, there is also a need for suitable tools to characterize such transducers. However, despite the importance of acoustic characterization to assess the performance of novel transducer arrays, the characterization process of highly complex transducers might involve various manual steps, which are laborious, time-consuming, and subject to errors. These factors can hinder the full characterization of a prototype transducer, leading to an under-representation or inadequate evaluation. To come to an extensive, high-quality evaluation of a prototype transducer, the acoustic characterization of each transducer element is indispensable in both transmit and receive operations. In this paper, we propose a pipeline to automatically perform the acoustic characterization of a matrix transducer using a research imaging system. The performance of the pipeline is tested on a prototype matrix transducer consisting of 960 elements. The results show that the proposed pipeline is capable of performing the complete acoustic characterization of a high-element count transducer in a fast and convenient way.

This article presents a compact analog front-end (AFE) circuit for ultrasound receivers with linear-in-dB continuous gain control for time-gain compensation (TGC). The AFE consists of two variable-gain stages, both of which employ a novel complementary current-steering network (CCSN) as the interpolator to realize continuously variable gain. The first stage is a trans-impedance amplifier (TIA) with a hardware-sharing inverter-based input stage to save power and area. The TIA's output couples capacitively to the second stage, which is a class-AB current amplifier (CA). The AFE is integrated into an application-specific integrated circuit (ASIC) in a 180-nm high-voltage BCD technology and assembled with a 100 μm-pitch PZT transducer array of 8 × 8 elements. Both electrical and acoustic measurements show that the AFE achieves a linear-in-dB gain error below ±0.4 dB within a 36-dB gain range, which is > 2 × better than the prior art. Per channel, the AFE occupies 0.025 mm2 area, consumes 0.8 mW power, and achieves an input-referred noise density of 1.31 pA/√Hz.

Three-dimensional ultrasound has initially been used to address volumetric imaging for diagnostic purposes and represents the leading-edge technological orientation in both transducer and IC (integrated circuit) architecture and design. However, new applications are coming up like biomarker measurements, preoperative navigation, real time surgery guidance or therapeutic procedures where 3D ultrasound modalities are key but their design objectives may need to be thought outside 3D echocardiography and radiology technological trade-offs. For those new applications, system architectures would need less complexity and imaging performances enabling easier hardware reconfigurability tailored to application-oriented imaging. This paper presents an ongoing development where a large matrix transducer has been assembled with multiple ASIC dies in a reconfigurable way. The transducer has a central frequency of 8MHz, a square pitch of 150μm× 150μm capable to fully image the upper carotid window thanks to a large aperture of 80×240 elements, resulting in a transducer active footprint of 12×36 square millimeters.

This work describes an ASIC design for high-frame-rate 3D intracardiac echocardiography probes. The chip is the first to combine element-level high-voltage pulsers and time-gain-compensation analog frontends as well as subarray beamformers and in-probe digitization in a pitch-matched fashion. The integration challenge is met by a shared hybrid beamforming ADC with the highest reported area and power efficiency. The achieved beamformer size of three elements enables acquisition at 1000 volumes/s while, in combination with a custom datalink, still providing sufficient channel-count reduction for catheter integration.

Ultrasonic flow meters (UFMs) based on transducer arrays offer several advantages. With electronic beam steering, it is possible to tune the steering angle of the beam for optimal signal-tonoise ratio (SNR) upon reception. Moreover, multiple beams can be generated to propagate through different travel paths, covering a wider section of the flow profile. Furthermore, in a clamp-on configuration, UFMs based on transducer arrays can perform self-calibration. In this manner, userinput is minimized and measurement repeatability is increased. In practice, transducer array elements may break down. This could happen due to aging, exposure to rough environments, and/or rough mechanical contact. As a consequence of inactive array elements, the measured transit time difference contains two offsets. One offset originates from non-uniform spatial sampling of the generated wavefield. Another offset originates from the ill-defined beam propagating through a travel path different from the intended one. In this paper, an algorithm is proposed that corrects for both of these offsets. The algorithm also performs a filtering operation in the frequency-wavenumber domain of all spurious (i.e., flow-insensitive) wave modes. The advantage of implementing the proposed algorithm is demonstrated on simulations and measurements, showing improved accuracy and precision of the transit time differences compared to the values obtained when the algorithm is not applied. The proposed algorithm can be implemented in both in-line and clamp-on configuration of UFMs based on transducer arrays.

Common clamp-on ultrasonic flow meters consist of two single-element transducers placed on the pipe wall. Flow speed is measured noninvasively, i.e., without interrupting the flow and without perforating the pipe wall, which also minimizes safety risks and avoids pressure drops inside the pipe. However, before metering, the transducers have to be carefully positioned along the pipe axis to correctly align the acoustic beams and obtain a well-calibrated flowmeter. This process is done manually, is dependent on the properties of the pipe and the liquid, does not account for pipe imperfections, and becomes troublesome on pipelines with an intricate shape. Matrix transducer arrays are suitable to dynamically steer acoustic beams and realize self-alignment upon reception, without user input. In this work, the design of a broadband 37×17 matrix array (center frequency of 1 MHz) to perform clamp-on ultrasonic flow measurements over a wide range of liquids (c=1000-2000m/s, α≤1 dB/MHz · cm) and pipe sizes is presented. Three critical aspects were assessed: efficiency, electronic beam steering, and wave mode conversion in the pipe wall. A prototype of a proof-of-concept flowmeter consisting of two 36-element linear arrays (center frequency of 1.1 MHz) was fabricated and placed on a 1-mm-thick, 40-mm inner diameter stainless steel pipe in a custom-made flow loop filled with water. At resonance, simulated and measured efficiencies in water of the linear arrays compared well: 0.88 and 0.81 kPa/V, respectively. Mean flow measurements were achieved by electronic beam steering of the acoustic beams and using both compressional and shear waves generated in the pipe wall. Correlation coefficients of R2>0.99 between measured and reference flow speeds were obtained, thus showing the operational concept of an array-based clamp-on ultrasonic flowmeter.