This article presents a low-noise transimpedance amplifier (TIA) designed for miniature ultrasound probes. It provides continuously variable gain to compensate for the time-dependent attenuation of the received echo signal. This time-gain compensation (TGC) compresses the echo-signal dynamic range (DR) while avoiding imaging artifacts associated with discrete gain steps. Embedding the TGC function in the TIA reduces the output DR, saving power compared to prior solutions that apply TGC after the low-noise amplifier. The TIA employs a capacitive ladder feedback network and a current-steering circuit to obtain a linear-in-dB gain range of 37 dB. A variable-gain loop amplifier based on current-reuse stages maintains constant bandwidth in a power-efficient manner. The TIA has been integrated in a 64-channel ultrasound transceiver applicationspecific integrated circuit (ASIC) in a 180-nm BCDMOS process and occupies a die area of 0.12 mm 2. It achieves a gain error below ±1 dB and a 1.7 pA/ √ Hz noise floor and consumes 5.2 mW from a ±0.9 V supply. B-mode images of a tissue-mimicking phantom are presented that show the benefits of the TGC scheme. Index Terms-Continuous gain control, time-gaincompensation (TGC), transimpedance amplifier (TIA), ultrasound application-specific integrated circuit (ASIC), ultrasound imaging. I. INTRODUCTION U LTRASOUND imaging is a safe and cost-effective tool for the diagnosis of medical conditions and the guidance of treatment. Size reduction of imaging devices has enabled ultrasound imaging from the tip of an mm-size catheter, for instance, for intracardiac echocardiography (ICE), as illustrated in Fig. 1(a) [1], [2]. Applications of ICE probes include guidance and monitoring of catheter ablation for the treatment of atrial fibrillation, guidance of closure of atrial septal defects, and guidance of transcatheter valve implantation [3], [4].

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