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Digital control of force microscope cantilevers using a field programmable gate array

Rev. Sci. Instrum. 79, 123705 (2008); doi:10.1063/1.3043432

Published 12 December 2008

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Jonathan P. Jacky,1 Joseph L. Garbini,2 Matthew Ettus,3 and John A. Sidles1
1Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington 98195-6500, USA
2Department of Mechanical Engineering, University of Washington, Seattle, Washington 98195-2600, USA
3Ettus Research LLC, Mountain View, California 94040, USA
This report describes a cantilever controller for magnetic resonance force microscopy based on a field programmable gate array, along with the hardware and software used to integrate the controller into an experiment. The controller is assembled from a low-cost commercially available software defined radio device and libraries of open-source software. The controller includes a digital filter comprising two cascaded second-order sections (“biquads”), which together can implement transfer functions for optimal cantilever controllers. An appendix in this report shows how to calculate filter coefficients for an optimal controller from measured cantilever characteristics. The controller also includes an input multiplexer and adder used in calibration protocols. Filter coefficients and multiplexer settings can be set and adjusted by control software while an experiment is running. The input is sampled at 64 MHz; the sampling frequency in the filters can be divided down under software control to achieve a good match with filter characteristics. Data reported here were sampled at 500 kHz, chosen for acoustic cantilevers with resonant frequencies near 8 kHz. Inputs are digitized with 12 bit resolution, and outputs are digitized with 14 bits. The experiment software is organized as a client and server to make it easy to adapt the controller to different experiments. The server encapsulates the details of controller hardware organization, connection technology, filter architecture, and number representation. The same server could be used in any experiment, while a different client encodes the particulars of each experiment. ©2008 American Institute of Physics
History: Received 3 September 2008; accepted 17 November 2008; published 12 December 2008
Permalink: http://link.aip.org/link/?RSINAK/79/123705/1
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KEYWORDS and PACS

Keywords
PACS
  • 07.57.Pt
    Submillimeter wave, microwave and radiowave spectrometers
  • 84.30.Sk
    Pulse and digital circuits
  • 07.05.Dz
    Control systems in physics
  • 84.40.Ua
    Telecommunications: signal transmission and processing; communication satellites
  • 84.30.Vn
    Filters (electronic circuits)
  • YEAR: 2008

PUBLICATION DATA

ISSN:
0034-6748 (print)   1089-7623 (online)
Publisher:
AIP is a member of CrossRef AIP

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