Notes from using the Analog Discovery 3 

By Dave Erickson

Intro: Why Analog Discovery?

AD3 Intro

Dave Jones does a very nice intro and teardown for the the Analog Discovery 3. Check it out. It is basically a complete electronics lab in a small $400 portable box. And it has some fairly advanced capabilities. I originally bought it to generate waveforms and digitize signals, and do some GPIO. But it is so much more than that. It is a 2 channel oscilloscope, voltmeter, WFG, Power Supply, Spectrum and Network analyzer, Impedance analyzer, Curve tracer, Logic analyzer, digital pattern generator, and more.

AD3 Network and Impedance analyzers

Measuring frequency response (Bode plots) and impedance plots can be expensive and time consuming. When I was a young pup in the late 80s, I designed a PC/AT plug-in board that could do frequency response plots up to about 5MHz. It used a DDS sine wave generator FPGA plus DAC, an RMS-DC converter and a slow ADC to measure the output. It controlled the hardware and plotted the data using Turbo C. Ah, the good old days.

Since then, when I need to plot frequency response, I set a waveform generator to the required frequency, measure using a DMM (or a scope, or a spectrum analyzer), and hand-enter the data into Excel. Then step-and-repeat.

Having the ability to do frequency response plots and impedance plots is powerful and convenient. Many times I have manually plotted frequency response, one frequency and measurement at a time, then entering the data into Excel. Some modern 'scopes with built-in waveform generators can do this nicely. For audio stuff, I have used REW and a decent sound card, but it only does up to the audio range. With its 14 bit, 125MHz  DACs and ADCs, the AD3 does the job nicely up to 25MHz: 3 orders of magnitude more than a sound card.

For audio, a proper audio analyzer (Audio Precision or Quant Asylum), or a sound card + REW will do it.

At my day job, we used the HP/Agilent 4395A up to 100MHz or so. This powerful instrument can do spectrum / network  / impedance analysis up to 500MHz. Its big brother, the HP4396A can do up to 1.8GHz. These instruments are about 20 years obsolete. I did a web page about repairing two HP 4395A power supplies. With the high-frequency impedance adapter HP 41951 and the right option installed,  It can measure SMT parts to 500MHz, thank you very much.  The HP4396A can do 1.8GHz. Here is the HP/Agilent 4395A I am quite familiar with.



When you add impedance plots, the instruments get more expensive. Keysight has a number of obsolete instruments, but just one modern Impedance analyzer, the E4990A. It does impedance analysis to 120MHz.  I see a few listed on Ebay for about $37,000 used, $75,000 new. It does not do network or spectrum analysis.  In fact, I don't see any new combined Spectrum / Network / Impedance analyzers on the market. For RF, the new tiny VNAs can do it.

Or you can buy a specific Bode plot instrument such as the Omicron Bode 100 for about $7,000. It will do up to 50Mhz.

The new mixed-signal scopes with function generators can be set up to do this automatically. But I don't have one of these. Nor do I have a large network analyzer at home.

Each instrument will do a pretty specific job. But the AD3 is quite general purpose. It does near DC to 25MHz, good for audio, Video, some RF, and any control loops. It does component testing nicely.

Here is a brief comparison of a handful of impedance analyzers.

AD3 Impedance analysis

The AD3 impedance analyzer is a real treat. It does from near DC to 25MHz with about 1% accuracy. The Analog Discovery Impedance Analyzer Adapter is a bargain at $25 and provides 6 relay-switched current sense resistor ranges.


I am using used it to measure transformers, capacitors, inductors, and resistors up to 25MHz. It does a great job on speakers, ultrasonics, crystals, or other complex devices. Even wire and cables.
At 25MHz, you can measure see the effect of 1cm of lead length on a ceramic capacitor.

It is 2 leads, not a full 4-lead Kelvin connection, but it has opens and short calibration of all ranges and frequencies, so can easily compensate for long leads. Since the AD3 'scope inputs are differential, they sense DUT current and voltage at the 2 contact points, quite well.

Here is the Z, Xs and Phase measurement data for a 270uH air-core inductor for a speaker crossover. You can clearly see the resonant frequency where the parallel capacitance of the inductor kicks in.