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ADA2200 Lock-In Amplifier

This project will attempt to explore and explain the use of the Analog Devices ADA2200 to build Lock-in Amplifiers.

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A Lock In Amplifier using the ADA2200 is a key part of my Spectrophotometer Project. While it seemed to work satisfactorily, I didn't ever feel like I really mastered it. There have been a few questions about the Lock In Amp that have inspired me to investigate it further and try to really understand it. This project will focus on the use of the ADA2200 specifically and will explore its operation using some support circuitry and trying some classic Lock In Amp experiments.

In general, here is how I expect this project to go. Details will be added here as they develop. As each step happens, I'll add a Project Log.

Step 1: Required reading - data sheet and Eval board description.  A Teensy 3.X will be used to do the configuration, clocking, and the sampling. The design used in the Spectrophotometer will be copied for the output; the input side will be new.
Design question: Should inputs be single ended or differential?
Design question: How should the RCLK output be conditioned to use as a signal source?

Step 2: Introductory Experiments that I want to try on the first design. What features should the board have for these? This step also yields the test signals / noise source that will be used.

Step 3: Initial design. How to partition the design? Are pre-amp and filters separate boards? Design board(s) and order parts.

Step 4: Build and Test! What works and what doesn't? What can I learn about using quadrature?

Step 5: Let's build a milliohm meter! Seems like a worthy goal.

Step 6: Let's measure an LED's response (classic experiment)! Another worthy goal.

Step 7: Evaluate results and redesign as needed.

ADA2200.pdf

Data sheet for the part I will use. This basically IS the lock in amplifier. Everything else can be considered support circuitry.

Adobe Portable Document Format - 636.92 kB - 10/24/2017 at 01:04

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ADA2200-EVALZ_UG-702.pdf

Description of the Evaluation Board that Analog Devices sells for this part. I intend to shamelessly copy from this to build test circuits.

Adobe Portable Document Format - 326.47 kB - 10/24/2017 at 01:04

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lock_in_amplifier.pdf

This a nice Apps Note from Analog Devices that explains how the Lock In Amp works and shows some alternative circuits.

Adobe Portable Document Format - 218.60 kB - 10/24/2017 at 01:04

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  • Getting Started with the Lock In Amp

    doctek10/24/2017 at 01:03 0 comments

    Time to get started! The ADA2200 Data Sheet and the ADA2200SDP-EVALZ-UG-787 explain the part I plan to use and show an evaluation board design that I will use for guidance. In addition, the design in https://hackaday.io/project/12491-spectrophotometer will be used especially for the output connection to the Teensy. The Teensy is not required. Other control schemes could easily be used.

    To aid understanding, the Data Sheet has a good explanation of the operation of a Lock In Amplifier. The Orozco article (lock_in_amplifier.pdf) has another good explanation. Together, they should provide a basic understanding. There are many other papers that offer more academic and mathematical explanations, but these can be read later.

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