Many Functions, One Tool: The Analog Discovery 2 from Digilent

AAC's Robin Mitchell discusses the capabilities of Digilent's Analog Discovery 2 test-and-measurement tool.

Anyone doing electronics as a profession, education, or a hobby will eventually need to upgrade their hardware and start to look into equipment such as oscilloscopes, logic analyzers, and function generators. Unless you're prepared to make this equipment yourself, you can expect to spend hundreds (if not thousands) of dollars for desktop standalone units.
Of course, this is only half the problem. What about space? This type of tech can really eat away at desk space, which is often in short supply.

This is where Digilent has stepped in and created their latest desktop product, the Analog Discovery 2 (or AD2, as I'll refer to it in this article). This device connects to a standard USB port and has many built-in functions including an oscilloscope, a logic analyzer, a spectrum analyzer, a function generator, a power supply, and a pattern generator.

Special thanks to Digilent for providing an Analog Discovery 2 for use with this article.

Overview

The AD2 comes packed with a lot of useful features for students and professionals alike.

• Two-channel differential input oscilloscope (±25V, 30MHz bandwidth)
• 16-bit logic analyzer
• Voltmeter (AC, DC, ±25V)
• Two-channel arbitrary function generator (±5V)
• Network analyzer
• Spectrum analyzer
• Digital bus analyzer
• Programmable power supplies

WaveForms 2015

Digilent provides WaveForms 2015 for free on their website. The software is easy to install and is available for Windows, Mac, and Linux.
There are no drivers needed for the AD2; either these are installed during setup or the AD2 uses a generic virtual COM port to communicate with WaveForms 2015.

WaveForms 2015. Click for larger image

Upon running WaveForms 2015, you will find a very “IDE-like” layout with tools that you can choose from running down the left side.
The options that are available include:

• Scope
• Waveform generator
• Power supply
• Logger
• Logic analyzer
• Pattern generator (for digital signals)
• Static IO
• Network analyzer (Bode plots, etc.)
• Spectrum analyzer
• Script (JavaScript)

WaveForms 2015 allows you to save workspaces, which is very convenient if you have a typical preferred layout of tools or are working across multiple projects. For example, you may have a digital environment where you are using the logic analyzer and have configured the AD2 to maximize its logic storage, or you are in the analog world where a spectrum analyzer and function generator are both needed.
The software automatically syncs with the AD2 upon connection, but it's more convenient to connect the AD2 before running WaveForms 2015.

Oscilloscope

The AD2's oscilloscope has two channels each capable of ±25V input at 30MHz bandwidth. Using the software for the oscilloscope is very similar (if not identical) to using a typical dedicated bench scope. All of the standard controls are available including:

• Channel enables
• Offset
• Range
• Time position
• Time base
• Single capture
• Repeated capture
• Streaming
• Screen shift
• Triggering
• Trigger channel selection (or external trigger)

The oscilloscope screen. Click for larger image

To better utilize the AD2, the device can be configured so that more of the onboard AD2 memory is dedicated to analog data storage as opposed to digital data storage. This allows for faster sample rates over a longer period of time.

The device manager that allows you to use different configurations to optimize sample rates

The AD2 has a max sample rate of 100MS/s (millions of samples per second) and, by changing the stream settings until samples are not lost, we get a maximum of 10MHz sample frequency at 10,000 samples. This gives us the ability to collect data at 10MHz for 1ms. As the sample rate is reduced, the number of samples goes up.

Sample Rate	Number of Samples	Recording Time
10MHz (Max)	10,000	1ms
5MHz	15,000	3ms
1MHz	1,000,000	> 1s

For sample frequencies lower than 2MHz, it appears that the AD2 can stream data over USB faster than samples come in from the oscilloscope, such that there is no need to use onboard storage for samples.

Logic Analyzer

The AD2 logic analyzer can record up to 16 individual channels simultaneously. The IO pins for the analyzer are compatible with 1.8V and 3.3V logic, but they are also 5V tolerant, which is particularly useful for many hobby projects that still rely on 5V (the Z80 for example). WaveForms 2015 has four main methods of operation for the logic analyzer:

• Repeated
• Shift
• Screen
• Stream

The logic analyzer layout. Click for larger image

The logic analyzer can also be made to trigger as a result of a customizable event. This trigger can be any of the following:

• A digital signal from an IO pin
• Patterns (such as a specific clock pattern with I2C)
• Software trigger from WaveForms 2015
• External trigger (found as an input on the AD2)

WaveForms 2015 also includes bus decoding and allows for many common bus configurations including:

• Parallel bus
• SPI
• I2C
• UART
• CAN
• I2S
• Custom – define your own protocol

The first three methods of operation (repeated, shift, and screen) have automatically determined sample rates, but the stream operation is configurable. If sample rates greater than 1MHz are used, then the sample size will depend on the sample rate.

Sample Rate	Samples	Time
10MHz	10,000	1ms
5MHz	100,000	20ms
1MHz	1,000,000	> 1s

Power Supplies

The AD2 includes a power supply that it derives from either the USB cable or an external wall wart that is plugged into the DC socket found on the back of the AD2. This power supply provides either a single supply at full power or a split supply at half power for each rail.
The voltages of the rails are also programmable from -5V to 5V, which makes the AD2 compatible with split-supply analog applications, 5V digital projects from the distant past, and modern low-voltage logic circuits.

AD2 Power Supply	Rail Mode	Power / Rail
USB	Single	500mW
USB	Dual	250mW
External Wall Wart	Single	2.1W
External Wall Wart	Dual	700mW

Power window in WaveForms 2015

WaveForms 2015 has a very simple interface for power supply control. Each rail can be turned on and off individually and set to a specific voltage ranging from 500mV to 5V for the positive rail and -500mV to -5V for the negative rail. The “Master Enable” button enables or disables both rails simultaneously.

Arbitrary Function Generator

The AD2 has two separate function generators; the output voltage range is ±5V, the sample rate is 100MS/s, and the bandwidth is 20MHz.
The available waveforms include

• DC
• Sine
• Square
• Triangle
• Ramp up
• Ramp down
• Noise
• Trapezoid
• Sine power

The two separate function generator screens. Click for larger image

The two function generators can either run independently or be synchronized to each other or to an external signal. Triggering for the function generator can be based on various sources including the oscilloscope, patterns, the PC, the logic analyzer, and one of the two external triggers.
The WaveForms 2015 screen for the waveform generators has most of the controls that one would expect to see on a standalone benchtop function generator. Controls include frequency, amplitude, offset, symmetry, and phase. The phase feature is handy when the function generator is synchronized to an external source.

Pattern Generator

The pattern generator on the AD2 converts the 16 IO lines that are used by the logic analyzer into a customizable digital pattern generator. This allows for outputs such as constants, pulses, clocks, random signals, and specific patterns.
The customized patterns are made by pointing and clicking with the mouse. The desired design can essentially be “painted” without the need for a scripting language or other less-intuitive input methods. Outputs can be configured to either be 1, 0, or high impedance (Z). The outputs can also be configured in the following way:

• PP – Push Pull
• OD – Open Drain
• OS – Open Source
• TS – Three State

One exceptional feature of the AD2 is the use of ROM logic whereby selected IO on the AD2 are configured as inputs and outputs. The output then depends on the input which is determined by the user via truth tables. This makes it possible to use the AD2 as a state machine or programmable logic array for simple applications.

The ROM window feature

Triggering of the pattern generator can be based on multiple sources, the runtime can be specified (20ns to 24 hours), and the beginning of the pattern can be preceded by a delay (20ns to 24 hours).

WaveForms 2015 pattern-generator window. Click for larger image

Other Analog Tools

The AD2 also includes a spectrum analyzer and a network analyzer with Bode plot capabilities. Each of these tools can be used for analysis up to 10MHz and are available for each oscilloscope channel input.

WaveForms 2015 showing two channels of spectrum analysis. Click for larger image

The spectrum analyzer has the following capabilities:

• Noise floor
• SFDR
• SNR
• THD

The network analyzer has the following capabilities:

• Bode plots
• Nyquist plots
• Nichols transfer diagrams

Summary

The AD2 is a compact USB-based test-and-measurement device that is compatible with Windows, Mac, and Linux. It offers a diverse collection of tools at a reasonable price and in some cases could be an effective replacement for typical benchtop equipment.