A Low-Cost Digital Phase-Sensitive Amplifier based on the MSP-430 Ultra-Low Power Microcontroller

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A Low-Cost Digital Phase-Sensitive Amplifier
based on the MSP-430 Ultra-Low Power
Microcontroller

• José J. Díaz
• Héctor Galloza
• Javier Morales

Sponsored by
Advisors Dr. Manuel Toledo Dr. Manuel
Jiménez Dr. Rogelio Palomera
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Overview

• Objectives
• Description
• Approach
• Work Status
• Future Work
• Acknowledgements

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Objectives

• Use of microcontroller to perform most
  phase-sensitive operations digitally.
• Low Cost
• Small Packaging
• Develop stand-alone unit with desired modularity.
  
• Perform phase-sensitive operations with the
  Microcontroller.

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Objectives (cont.)

• Generate reference signal internally.
• Computer interface for interpretation of data.
• Flexibility.

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Lock-In Amplifier

• Signal produced by reference excitation.
• Embedded in noise
• Reference and produced signals are correlated
• Widely-used by scientists to perform experiments
  without noise effects.
• Commercial lock-in amplifiers range from hundreds
  to several thousands dollars!

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Lock-in Amplifier
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Lock-In Amplifier (cont.)
Signal Generation Stage
Phase-Sensitive Operations Stage
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Approach

• MATLAB
• High-level language
• Easily verifiable
• MATLAB code ? C/Assembly Language
• Focus on the reference signal

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MATLAB Code
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Signals Generated
Discrete Signal
Digital Signal
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Work Done

• Reference Signal Sinusoid
• Convert the digital signal received from MSP430
  to analog signal using a DAC.
• Recovery the signal using the internal ADC of the
  MSP430.

MSP-430

DAC
8-bits
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Analog-to-Digital Issues
A/D Channel
MSP-430
Recovered Signal

• Anti-Aliasing Filter

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Filtering Software

• Difference Equation for low-pass filter
  implementation

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Example Application of Lock-In Detection

• Photoconductivity Experiment.
• Semiconductor is cooled down ? becomes insulator
• Sample illuminated with monochromatic light
• Monitor conductivity with changes in wavelengths,
  energy spectrum obtained
• Analysis yields information about impurities and
  crystal defects in the material
• Phase-Sensitive detection often used as data is
  usually immersed in noise.

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Potential Design Problems

• Memory Issues
• Not enough memory
• Power Issues
• Power consumption needs to be optimized to
  achieve goals

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Work Status

• Sinusoid generation completed.
• Signal recovery completed.
• Phase detection between reference and recovered
  signals in progress.
• Phase-Sensitive operations in progress.

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Future Work

• Add desired flexibility to our design.
• Frequency and Magnitude Control
• Introduce to the design a LCD and Keypad to
  control our design.
• Develop interface for computer.

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Acknowledgements

• Dr. Manuel Toledo
• Everyone _at_ ICDL
• Industrial Affiliates Program

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Questions?