Development and Implementation of a FPGA-based digital beamformer

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Development and Implementation of a FPGA-based
digital beamformer Supervisors Nandita
Bhattacharjee Dr.
Andrew Paplinski
Dale Harders
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• Presentation Outline
• An Ultrasonic Imaging System Overview
• Beamforming Fundamentals
• Significance of study
• Simulator role within this project
• Implementation

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Ultrasonic Imaging System Overview
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Beamforming Fundamentals
What is a beamformer?

• Spatial Filter
• Only extract desired directional data
• Remaining signals are attenuated

• Focussing subsystem
• Electronic vs. Mechanical
• Sharper images are produced

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Beamforming Fundamentals
How is this focussing achieved digitally?
Consider how an ultrasonic imaging system
operates
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Beamforming Fundamentals
Possible Solution Delay in time
Disadvantages Large storage requirements
High clock rates required for fine delays
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Beamforming Fundamentals
Better Solution Phase-shift via complex vector
rotation

• A rotation of complex data in the frequency
  domain is equivalent to a time delay in the time
  domain.

• Process data in a different Domain
• requires Quadrature sampling (Re, Im)

Advantages Relatively small digital circuitry
required Lower sampling rates required
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Significance of Study
Ultimate Goals

• Increase Image Resolution
• - Improve Signal-to-noise ratio
• Maintain fast frame-rates
• - Real-time imaging
• Develop 3D-imaging techniques

• Continuation of Previous Research _at_ Monash
• (Hampson G, 1998), (Bhattacharjee et al, 2000)
• (Prain R, 2001)

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Simulator role within this project
Field II
(Jensen, 1996)

• Ultrasound simulation program
• Developed by Joergen Jensen, Denmark
• Running under Matlab
• Capable of emulating all sub-systems

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Simulator role within this project
Field II Example
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Simulator role within this project
Field II Example
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Simulator role within this project
Field II Example
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Implementation

• Hardware system
• Two word-parallel, fully pipelined, CORDIC vector
  rotators operating in parallel
• Summing performed on chip
• Design implemented on a Xilinx Spartan II FPGA

• Device Driver
• Interfaced PCI communications API to Matlab

Developed System - Block Schematic Next Slide
Dale Harders
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Beamformer System

ACCUMULATOR
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Conclusion

• Stable Development Platform built
• Easy to use interface for new design
  test-benching

• Project deliverables satisfied
• Successfully implemented a hardware digital
  beamformer

• PCI communications
• Developed a PCI communications interface between
  Matlab and the Hardware for design verification
  and future development acceleration

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References Bhattacharjee N, Paplinski A and
Hampson G, "Phase-shift Beamforming", TR
2000/53, CSSE , Monash University, Clayton,
2000 Hampson G.A, "Implementing
Multi-Dimensional Digital Hardware
Beamformers", PhD thesis, Faculty of Computing
and Information Technology. Monash University,
Clayton, 1998. Jensen J.A, "Field A
program for simulating ultrasound systems", 10th
Nordic-Baltic Conference on Biomedical
Imaging, vol 4, pg 351-353, 1996. Prain R,
Parallel CORDIC implementation for hardware
beamformers, Honours Thesis, Department of
CSSE, Monash University, Clayton, 2001.
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