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 x unipolar output voltage. The power converter employs an adaptive Delta I 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-mu m 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.