An Integrated High-Voltage Low-Distortion Current-Feedback Linear Power Amplifier for Ultrasound Transmitters Using Digital Predistortion and Dynamic Current Biasing Techniques

Abstract

A novel integrated high-voltage linear power amplifier for medical ultrasonic transmitter applications is presented in this brief. The amplifier employs a current-feedback technique with two cascading push–pull class-AB buffers. It overcomes the gain–bandwidth product limitation of a conventional voltage-feedback amplifier, capable of generating high output signal swing with a wide closed-loop bandwidth. In addition, a dynamic current biasing topology is integrated on-chip using a voltage-controlled current source and a 7-bit digital-to-analog converter (DAC). To further improve the signal linearity of the amplifier output, a digital predistortion (DPD) technique is applied by using a DAC, an analog-to-digital converter, and a digital field-programmable gate array. The presented amplifier was fabricated using a 1- $\mu\hbox{m}$ 200-V CMOS process. The measurement results show that this integrated linear power amplifier is capable of driving a load of a 100- $\Omega$ resistor in parallel with a 300-pF capacitor while achieving a signal swing up to 180 $V_{\rm pp}$ with a second-order harmonic distortion as low as $-$ 50 dB. Measurement results also show that the amplifier achieves a maximum slew rate of 4 V/ns and a power efficiency of 30%. As a result, this power amplifier is expected to greatly improve medical ultrasound image quality.