Emerging handheld and wearable ultrasound devices enable diagnosis and long-term monitoring outside clinical settings. They require a low-power, highly complex, locally integrated system to process the RF data. The analog-to-digital converter (ADC) is a critical building block in the receive chain of these systems as it enables digital beamforming and image reconstruction. However, the ADCs currently used in cart-based imaging systems are bulky and consume too much power to be integrated into battery-powered devices. This article investigates how the area and power consumption of the commonly used successive approximation register (SAR) ADC can be reduced without negatively affecting B-mode and color-Doppler image quality. A Monte Carlo (MC) simulation study was performed in which RF data acquired with a phased-array transducer in Field II were digitized using a model of a nonideal ADC. Five different nonidealities were applied to four commonly used SAR-ADC architectures. B-mode and color-Doppler images were reconstructed from the digitized RF data. The impact of the nonidealities on the image quality was evaluated by means of three image quality metrics (IQM): peak signal-to-noise ratio (PSNR), structural similarity index (SSIM), and contrast-to-noise ratio (CNR). The effectiveness of error correction and ways of calibration are also discussed. The results show that both B-mode imaging and color-Doppler imaging are inherently resilient to nonidealities, particularly capacitor mismatch, leading to relaxed ADC requirements and paving the way for more practical in-probe digitization.

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.