An arbitrary waveform transmitter using bipolar pulsers based on a high order modified sigma delta modulation

Abstract

Coded excitation requires a complicated arbitrary waveform transmitter for each active channel which generally uses a multi-bit digital-to-analog converter(DAC) and a linear power amplifier(LPA). Not only does the LPA increase the cost and size of a transmitter block, but it consumes much power, increasing the system complexity further and causing a heating- up problem. We present an efficient arbitrary waveform generator to solve these problems based on modified sigma-delta modulation(SDM) methods suitable for coded excitation techniques, which is composed of a 1bit DAC to generate single- bit SDM waveforms, a bipolar pulser to produce their high voltage versions, and a simple LC filter connected to array elements. The results showed that the proposed scheme can achieve a low oversampling ratio(OSR) of 4 (i.e., 80MHz switching rate), while the peak sidelobe level of the compressed waveform on receive should be smaller than -45dB.