An integrated high-voltage pulser with improved HD2 and programmable amplitude

Abstract

Miniature ultrasound probes increasingly employ ASIC that drive the transducer elements with HV pulses and process the received echo signals. Due to size constraints, the HV pulsers tend to be relatively simple circuits, in which HV MOS transistors pull the transducer element to a HV supply and back to ground. An important disadvantage of existing designs is that the rising and falling edges of the generated pulses are not well matched, which leads to second-harmonic components in the generated pulse. This makes these design unsuited for harmonic imaging. Moreover, the pulse amplitude typically cannot be controlled, making it difficult to apply apodization techniques that are often desired to reduce sidelobes. This work presents an ASIC design that addresses these disadvantages. The content discussed in this thesis includes the circuit architecture, circuit implementation and analysis of simulation results for an integrated HV pulser with improved HD2 and programmable amplitude enabling apodization. The design consists of two parts: a transmit driver and the HV pulser. The transmit driver, composed of a negative feedback loop with a replica pulser, a level shifter and other components, can generate a lower HD2 by auto-calibrating the pull-up and pull-down time. It can be shared by multiple HV pulsers that drive the transducer elements. A combination of duty-cycle modulation and slew-rate modulation is proposed for pulse-amplitude control. Finally, an experiment aimed to explore the effective acoustic power of transducer under high and low impedance drive modes is proposed. These drive modes are first investigate by simulating the transducer driven by an ideal current and an ideal voltage source. Then, an experimental circuit is proposed in which the transducer is connected to an OpAmp in different ways to achieve similar impedance conditions as in the ideal situation to verify whether there is a large gap in the acoustic power.