Non-linear harmonic reduction pulse width modulation (HRPWM) for the arbitrary control of transducer-integrated switched excitation electronics

Advances in electronics and transducer fabrication have provided the ultrasound system designer with the opportunity for integrating electronics into the transducer head. Switched mode circuits are miniaturizable, low loss and as such are suited to array excitation. Without careful excitation signal design switched mode waveforms lack combined time varying amplitude and harmonic control. Existing modulation schemes have provided either amplitude or harmonic control. The proposed harmonic reduction pulse width modulation (HRPWM) provides a method of creating a quinary (5-level) switched waveform with both time-varying amplitude control and third harmonic cancellation. HRPWM achieves waveform control through matching the amplitude of energy contained at the fundamental frequency with the desired amplitude, and third harmonic cancellation through the use of a non-linear modulating waveform. The resulting HRPWM excitation signals use multiple bipolar low voltage pulses for the control of signals below 50% magnitude, and a five-level pulse for amplitudes above 50%. In simulations, HRPWM shows an excitation signal third harmonic power of -34.75 dB, a reduction of 19 dB from other 5-level modulation schemes, and a ultrasound pressure waveform third harmonic power of -64.19 dB, a reduction of 19.9 dB from other 5-level modulation schemes, and 25 dB lower than bipolar switched excitation.