A 20-MHz 2.3-mW Receiver and a 25-V Transmitter for Ultrasound Capsule Endoscopy

Biomedical applications of ultrasound (US) imaging have been extended and diversified. Some recent applications, such as intracardiac echocardiography [1], [2] and the intravascular US [3], require extreme miniaturization of the US imaging system. As another promising application, an ultrasound capsule endoscopy (USCE) is being developed to provide transmural scans of the gastrointestinal tract and enable the detection of deeper pathology [4]. However, the USCE has only been studied by focusing on the transducer array, and ASIC research for US imaging in capsule endoscopy has not been conducted. Moreover, the USCE imposes stringent restrictions on not only the system size but also the power consumption because the imaging system should operate for long hours with tiny batteries (Fig. 1). In our work, an on-chip US transmitter (TX) and a highly power-efficient US receiver (RX) IC for USCE application are proposed. Instead of using a power-hungry high-speed ADC to acquire the US signal at a high center frequency $(\mathrm{f}_{\text{center}})$, we propose a new RX structure employing synchronized analog envelop detection (ED) to reduce the required ADC speed. A noise-shaping SAR (NS-SAR) ADC is used to improve power efficiency further while providing high resolution.