A 14V Hybrid Boost Converter With Scalable Conversion Ratio in 180nm Standard CMOS for an Ultrasound Imaging System

Ultrasound imaging, thanks to its light-insusceptibility, non-invasive and non-ionizing-radiation characteristics, has gained growing popularity in applications including unmanned vehicles and medical diagnosis [1]–[5]. Interfaced with transducers (e.g. PMUT, CMUT, etc) that demand high voltage ($20\mathrm{V} _{\mathrm{PP}}$ or higher [1]), the corresponding high voltage supply is essential for the driving circuits. Moreover, using standard CMOS provides more flexibilities on the digital processor integration and adoption of existing IPs, where the multi-voltage-domain driving signals and biasing voltages are also required to operate the driving circuits [3]–[5]. However, supplying the high voltage $( \gt10\mathrm{V})$ and the intermediate voltage domains in the standard CMOS process is challenging. Despite their relatively large conversion ratio, boost converters [6] have a limited single output voltage of 1.1V. While [7] achieves up to 20V regulated voltage, it does so in the HV process, limiting the circuit compatibility. Charge pump-based structure is employed in [8] for a 32V output, but this voltage is susceptible to load variations due to the lack of a feedback control mechanism. While [5] cascades the charge pump after a low-drop-out (LDO) to mitigate the output voltage variation with respect to the input, additional losses (due to the two-stage design) are introduced, and the loading-induced voltage variations still exist.