Design of Integrated Bipolar Symmetric Output DC–DC Power Converter for Digital Pulse Generators in Ultrasound Medical Imaging Systems

This paper presents a bipolar symmetric output switching dc-dc converter for digital pulse generators in ultrasound medical imaging systems. The proposed power stage architecture can generate symmetric bipolar supply voltages, while operating in a time-interleaving manner. Meanwhile, in order to power unipolar pulse generators with the same peak-to-peak pulse amplitude, the power stage can also be reconfigured to deliver a 2× unipolar output voltage. The power converter employs an adaptive ΔI charge balance control scheme to ensure that the outputs are symmetrically balanced and well regulated. At the circuit level, to utilize a single feedback controller for both power stage topologies, the assignment of a suitable chip ground is discussed. A prototype is fabricated using a 0.25-μm CMOS process and occupies a chip area of 6 mm ². For an input supply voltage of 1.5 V, the dc-dc converter can regulate the bipolar outputs at a nominal voltage level of ±2.5 V and at 5 V for the unipolar output configuration and a maximum load current of 45 mA for both. The bipolar output power converter achieves a maximum efficiency of 83.4% at a load power of 187.5 mW, with the voltage balance error maintained within ± 2% over the entire load range.