Noninvasive brain stimulation plays an essential role in diagnosing and treating diseases of the brain. This stimulation can affect disease-related changes in brain activation, inhibition, or connectivity. Ultrasound neuromodulation is a rapidly growing field of noninvasive brain stimulation. In a form of acoustic pressure waves, ultrasound can transmit mechanical forces to modulate neurons. The acoustic waves can be focused on a particular location with a spatial resolution that depends on the set frequency. Compared to other noninvasive brain stimulation methods, ultrasound neuromodulation is a safe and reversible method that can be used to accurately simulate neuronal circuits for the treatment of neurological diseases.

New medical ultrasound solutions, from ultrasound imaging to ultrasound neuromodulation and ultrasonic powering of medical implants, require a wearable form factor and low power consumption. In these applications, pulsers are the most power-hungry block since they deliver high voltages to the ultrasound transducers and transducers contain massive parasitic capacitance. The ultrasound transducer needs to be driven by a high voltage (HV) square wave so that it can generate desired pressure for ultrasound brain stimulation. Therefore, improving the power efficiency of the driver part is very important for the whole system.

The purpose of this thesis is to design an energy-efficient driver within a limited area. There are two energy-consuming parts in the driver circuit. One is the parasitic capacitance of HV transistors, and the other is the capacitance of the transducer. In order to achieve HV operations, the driver part is typically implemented with HV transistors which have massive parasitic capacitance and also consume large areas. To solve this problem, stacked 5 V CMOS transistors are implemented to replace HV transistors. As for the energy loss due to charging and discharging the ultrasound transducer, many energy-saving methods are introduced in the literature such as energy-replenishing technique, charge redistribution method, and multi-level pulse-shaping technique. The proposed design compared the advantages and disadvantages of these methods and made some improvements on the basis of these techniques.

This work presents a power-efficient high-voltage pulser to drive integrated lead zirconate titanate (PZT) ultrasound transducers for ultrasound medical applications. The proposed pulser employs charge redistribution technique by utilizing a storage capacitor to save part of the charges before discharging the transducer. Furthermore, HV transistors are replaced by stacked 5V CMOS transistors that allow delivering 10 V to the piezo transducer. The pulser is designed and simulated in 180nm CMOS technology with 10 V power supply and 15 MHz operating frequency. The simulation results demonstrate that the proposed circuit improves the power efficiency by 30.55$\%$ compared to the traditional class-D pulser.