Improved Ultrasound Harmonic Golay Encoding Using Pulse-Width-Modulation Transmit

摘要

Quadrature phase shift is required for ultrasound harmonic Golay encoding. Nonetheless, with a 3-level pulser system, typical square transmit waveform fails to reproduce the 90° phase shift and thus the resultant harmonic code is not accurately encoded as the phased-inverted symbols of +1 and -1. This introduces coding error and subsequent range side lobe artifacts after decoding. In this work, pulse-width modulation (PWM) of phased arbitrary transmit waveforms is applied in complementary Golay encoding to suppress peak range side lobe level (PRSL) in the pulser transmit system. Simulation results show that PWM transmit with high sampling rate (f_s=100f_0) provides the lowest PRSL but the PRSL increases rapidly when the sampling rate decreases. Compared to the typical square pulse (f_s=4f_0), the PWM waveform with sampling rate higher than 20 times f_0 can effectively suppress the PRSL for signal bandwidth of 20%. When the signal bandwidth increases to 50%, the PRSL deteriorates but still can be lower than the square pulse if the sampling rate is higher than 10 times f_0.