An FPGA-Based 15-level Arbitrary Waveform Generator System with Phase/Frequency Modulation for Ultrasound Coded Excitation Using Pulse-Amplitude Modulation (PAM)

Several research communities have presented innovative approaches to the challenge of generating complex waveforms required to evaluate new ultrasonic transmission techniques. Dedicated high-speed digital-to-analog converters combined with high-voltage (HV) power amplifiers are employed, although their design is relatively complicated. This paper presents a reconfigurable multi-level arbitrary waveform generator (AWG) for ultrasound-coded excitation research using Pulse-Amplitude Modulation (PAM). The proposed hardware architecture consists of a Terasic DE2-115 board coupled to the developed AWG daughterboard. The transmission board was implemented using state-of-the-art devices providing complete digital control, in which the main component is the MD2134 high-speed ultrasound source driver. The design includes an MD0100 HV T/R switch, a voltage-controlled gain wideband amplifier VCA810, and a 12-bit 80 MSPS ADC for pulse-echo applications. Testing results show that the AWG system can generate HV pulses (up to 200 Vpp) from 2 MHz to 10 MHz (central frequency). The conventional sinusoidal excitation pulses can reach a −6 dB relative bandwidth of 3.5% to 103.5%, and linear frequency modulated (LFM) chirp can be generated using different windowing functions with programmable duration (step of 0.1 μs) and taper ratio (0 to 100% with a step of 5%). The proposed PAM AWG system can be used to evaluate different phase/frequency modulated excitation methods and applications, such as pulse inversion and dynamic transmit focusing.