Integrated low-power CMFB-free variable-gain amplifier for ultrasound diagnostic applications

An integrated current-feedback variable-gain amplifier (VGA) suitable for low-power ultrasound diagnostic applications is presented in this paper, which provides variable gain to accommodate large input dynamic range of ultrasonic receiver. With a proposed active feedback technique, the amplifier maintains a constant bandwidth at different gain levels. Signal distortion due to the bandwidth shift is thus avoided. Compared to most Bipolar and BiCMOS counterparts, the proposed VGA is implemented in a low-cost CMOS process, without compromising the performance. In addition, it employs a resistive feedback network to automatically set the output DC voltage, without using any extra common-mode feedback (CMFB) circuits, making the design simple and effective. The proposed VGA was fabricated and tested with a standard 0.35-μm CMOS process, with an active die area of only 0.052 mm2. The static power dissipation is 2.18 mW with a power supply of 3.0 V. The VGA exhibits a constant bandwidth of 4.5 MHz with a variable gain ranging from 0 to 46 dB. The system is well stabilized with a phase margin of 71.3° at the worst case. Comparisons to the state-of-the-arts demonstrate very competitive performance of this work.