Wideband linear power amplifier for high-frequency ultrasonic coded excitation imaging

Linear power amplifiers are critical components in ultrasonic imaging systems that implement chirp-coded excitation. Bench-top commercial power amplifiers are usually used in academic laboratories for high-frequency ultrasound imaging, and the imaging performance depends greatly on these general-purpose instruments. To achieve a wide dynamic range, a power amplifier consisting of two stages is developed for chirp-coded ultrasound imaging applications through the implementation of custom-designed broadband 1:1 transformers and the optimization of feedback circuits. The amplifier has broad bandwidth (5 to 135 MHz), maintaining a linearity up to the 1-dB gain compression point (P1dB) of 41.5 dBm, allowing 16 dBm input power level at 60 MHz. The mean and the maximum values of output third-order intercept points (OIP3) are 51.8 and 53.5 dBm, respectively, between 20 and 110 MHz. With 12 dBm input power, the gain of the amplifier varies between 24 and 29 dB, offering a uniformity which would allow excitation of a 70-MHz single-element transducer with windowed chirp-coded bursts sweeping from 40 to 100 MHz. The performance in high-frequency ultrasound imaging is evaluated with a wire phantom. Echo signal-to-noise ratio (eSNR) of the designed amplifier is 7 dB better than a commercial amplifier, and spatial resolution is maintained.