High-voltage integrated Class-B amplifier for ultrasound transducers

High-voltage linear amplifiers driving transducers for ultrasound imaging enable apodization profiles with high resolution, beams with low harmonic content and instantaneous changes in transmit energy between pulses. In view of an increased level of integration, the availability of a BCD technology, capable of watts level driving at high frequency, encourages investigation of linear amplifiers, the topic of this work. A feedback amplifier with high voltage - high efficiency Class B output stage is proposed. Device parameters vary significantly with signal amplitude making circuit analysis more involved. We propose the use of describing functions to estimate the large-signal frequency response. Analytical results are in good agreement with simulations and provide useful design insights. From measurements, a test-chip in BCD-6 SOI displays 40.9dB gain, 90Vpk-pk output voltage with a minimum 3dB cut-off frequency of 5.5MHz. Quiescent power dissipation is 37mW only.