Abstract
BackgroundIn ultrasound imaging systems, the digital transmit beamformer is a critical module that generates accurate control over several transmission parameters. However, such transmit front-end module is not typically accessible to ultrasound researchers. To overcome this difficulty, we have been developing a compact and fully programmable digital transmit system using the pulse-width modulation (PWM) technique for generating simultaneous arbitrary waveforms, specifically designed for research purposes.MethodsIn this paper we present a reconfigurable arbitrary waveform generator (RAWG) for ultrasound research applications that exploits a high frequency PWM scheme implemented in a low-cost FPGA, taking advantage of its flexibility and parallel processing capability for independent controlling of multiple transmission parameters. The 8-channel platform consists of a FPGA-based development board including an USB 2.0 interface and an arbitrary waveform generator board with eight MD2130 beamformer source drivers for individual control of waveform, amplitude apodization, phase angle and time delay trigger.ResultsTo evaluate the efficiency of our system, we used equivalent RC loads (1 kΩ and 220 pF) to produce arbitrary excitation waveforms with the Gaussian and Tukey profiles. The PWM carrier frequency was set at 160 MHz featuring high resolution while keeping a minimum time delay of 3.125 ns between pulses to enable the acoustic beam to be focused and/or steered electronically. Preliminary experimental results show that the RAWG can produce complex arbitrary pulses with amplitude over 100 Vpp and central frequency up to 20 MHz with satisfactory linearity of the amplitude apodization, as well as focusing phase adjustment capability with angular resolution of 7.5°.ConclusionsThe initial results of this study showed that the proposed research system is suitable for generating simultaneous arbitrary waveforms, providing extensive user control with direct digital access to the various transmission parameters needed to explore alternative ultrasound transmission techniques.
Highlights
In ultrasound imaging systems, the digital transmit beamformer is a critical module that generates accurate control over several transmission parameters
In modern US systems the advanced excitation scheme employs arbitrary waveform generators (AWGs) [10], typically controlled by analog and digital custom application-specific integrated circuits (ASICs) or, more recently, reconfigurable technologies based on field-programmable gate arrays (FPGAs) [11]
In this paper we present a reconfigurable arbitrary waveform generator (RAWG) that exploits the pulse-width modulation (PWM) technique implemented in a low-cost FPGA for independent control of multiple transmission parameters
Summary
The digital transmit beamformer is a critical module that generates accurate control over several transmission parameters. Such transmit front-end module is not typically accessible to ultrasound researchers. Independent excitation of each piezoelectric element in a multielement US transducer can be performed with low second order harmonic distortions for modulated excitation imaging [10] As illustrated, this transmit technique requires additional expensive electronics, e.g., digital-to-analog converters (DACs), low-pass filtering (LPF) and linear high-voltage amplifiers (HV AMP) to translate the digital waveform to an amplified analog signal to drive the transducer elements, and generally reserved for more expensive and less portable high performance US systems. Most of these systems do not use this transmit beamformer technique, but instead use unipolar, bipolar or multilevel high-voltage pulsers to generate the necessary transmit signals [6]
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