A Variable-Gain Low-Noise Transimpedance Amplifier for Miniature Ultrasound Probes

Abstract

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].

Integrated Circuits for Medical Ultrasound Applications: Imaging and Beyond

“…(d) VGA using an interpolated ladder attenuator [114]. can be largely classified into two categories; amplifiers with discrete gain steps, also known as programmable gain amplifier (PGA), and amplifiers with continuous gain control, also known as variable gain amplifiers (VGA) [99].…”

“…This method is impractical as it would increase the chip area significantly. Other limitations include i) the changing input and output impedances of the PGA that could complicate the performance of inter-connected modules, ii) low operating bandwidth due to the close-loop configuration, and iii) switching artifacts in the ultrasound image from one discrete gain step to the next [99].…”

“…In order to achieve this dB-linear gain, VGAs can be broadly classified into two categories; amplifiers based on exponential approximation functions and amplifiers with interpolation between discrete gain steps [99]. In the first category, amplifiers achieve dB-linear gain by using the inherent linear and quadratic characteristics of MOSFETs to implement exponential approximation functions e.g.…”

Integrated Transceivers for Emerging Medical Ultrasound Imaging Devices: A Review

“…9c) [26], [45], [49], [50] and current amplifiers (CA) (Fig. 9d) [51] sense the current by establishing a low input impedance virtual ground. Therefore, in integrated systems, VA and TCA are usually used to interface with transducers with lower impedance (< 2 k ), such as PZTs [52], [53] and PMUTs [30], [46], while TIA and CA are commonly adopted for CMUTs and polyvinylidene fluorides (PVDF) transducers [54], [55] which often exhibit relatively higher impedance (> 10 k ) [56].…”

“…By controlling the voltage applied to the differential pair, a continuous interpolation to the current gain of the amplifier can be realized. This approach was first proposed in [68] and recently got demonstrated in a compact variable-gain ultrasound TIA with compelling gain linearity and noise-power efficiency [51].…”