If you see the word “arbitrary” in conjunction with a function generator, it signifies the instrument’s capability to customize waveforms at the user’s discretion. The new Tektronix AFG31000 Series arbitrary function generator incorporates this technology on top of its traditional library of a dozen basic waveforms: sine, square, ramp, pulse, noise, sin (x)/x, dc, Gaussian, Lorentz, exponential rise, exponential decay and Haversine.
The user can customize these conventional waveforms, creating an enormous number of variations. They can be modified as to frequency, amplitude and offset, and displayed in continuous, modulation or sweep mode, using a touchscreen or front panel controls. Then they can be exported via one or two channels for display in a second instrument, another AFG or oscilloscope, or they can be injected into electronic circuitry for signal tracing or product evaluation.
It really gets interesting when we create special waveforms, which can be modified after the fact and saved to internal memory or USB flash drive. This is accomplished by means of the instrument’s internal ArbBuilder software, eliminating the need for a connected computer.
To open a previously created waveform or to synthesize a new waveform, select the ArbBuilder icon.
1. Select Basic on the touch screen.
2. Swipe the arrow up at the bottom of the touch screen and select the ArbBuilder icon.
3. Select New.
4. Select Draw.
The horizontal menu at the bottom allows you to select Freehand, Horizontal, Vertical or Point. If you select Freehand, you can use your finger to draw a waveform. The capacitive touch screen does not respond to an insulated pointer, but you can use a hand-held conductive object provided that it has a sufficiently large area contacting the screen.
If you touch point, you can create a waveform by tapping the screen at discrete spots. Then you can touch Interpolate and make a linear, smooth or staircase trace. Undo and Delete can be used to backtrack.
A waveform can also be created using the equation that generates the associated function. To access this mode, touch Basic in the Home screen. Swipe up the arrow at the bottom. Then, touch the ArbBuilder tab on the right, followed by New. In the menu bar at the bottom, to the right of New Std., which refers to the internal waveform library, touch New Equation. The Equation Editor screen has two sections. On the left is Equation and on the right is Settings. Below is an on-screen keyboard.
The equation that you want to represent by a waveform is to be typed in the location indicated. If you touch anywhere in this box, a keyboard appears. A default equation, Sin(w), is provided as an example. You can use the backspace key to delete Sin(w) and enter your equation. To display either, touch X at the upper right corner of the keyboard to get it out of the way. Then, touch Compile in the lower horizontal menu.
In the equation box, Compiled Successfully! appears. To the right is a thumbnail preview of your wave. Touch OK to see the display of the wave that you created, along with its file name.
Now, in the lower horizontal menu, several choices are available. For example, you can touch Invert or Mirror to perform those actions, and touching them a second time reverts to the original. If you touch Draw, then Freehand, Horizontal, Vertical and Point become available. After touching Point, you can manually put points in the display. Then, touching Interpolate and Linear, you can make a perturbation in the waveform that you previously created by means of entering the equation. Touching Clear All removes the points, leaving the modified waveform. If you touch Draw>Freehand, further modifications can be made.
Equation Editor supports the basic seven-bit ASCII character set. The maximum length of a single string is 256 characters, including spaces. Strings may be concatenated at the end of a line by inserting a colon. The maximum length (sum of all strings) is 1,000.
You can save or send to Channel One or Channel Two the waveform you have created, along with any edits. To save the waveform, in the Save As dialog box enter a file name and select OK. The equation file will be saved in the .eqa file format. To open an equation file, in the Equation Editor window, select the Equation Editor toolbar. Select an existing equation file and touch Open.
An equation file can be edited. In the Equation Editor window, equations can be modified as follows:
1. Cut – Highlight the part of the equation you want to cut and select Cut.
2. Copy – Highlight the part of the equation you want to copy and select Copy.
3. Paste – Highlight the part of the equation you want to paste and select Paste.
4. Directly edit the text using a keyboard or the command list keypad.
5. With a waveform displayed, if you touch Copy or Paste, a green cursor appears at the left of the display and a red cursor appears at the right of the display. These cursors can be dragged toward the center and used to copy and paste.
Paste options are:
1. Paste at the end.
2. Paste at the beginning.
3. Paste at the active cursor.
4. Replace between the cursors.
The created waveforms, with all these modifications, can be sent to another instrument, such as an oscilloscope. With BNC cables connected to either or both AFG Channel One and Channel Two outputs and one or two oscilloscope analog channel inputs, and the applicable channels in both instruments turned on, in the AFG touch Send and convey the waveform(s) out through either or both channels. You can now move both cursors to the sides and perform additional edits on the arbitrary waveform that you created.
An arbitrary waveform can be modified: Select Basic on the Homepage. Swipe the arrow up at the bottom of the screen and touch the ArbBuilder tab. Select Open and choose the file you want to modify.
To open a file with ArbBuilder, select Open from the waveform tab. The file Open Dialog Box displays. Select an existing waveform file. ArbBuilder supports several file formats: wfm, csv, tfw and tfwx. You can open the selected file in a new tab. Select OK. The file opens.
ArbExpress is another piece of software that enables the user to create and edit waveforms for the AFG31000 Arbitrary Function Generator. It is a Windows-based application that can be downloaded free of charge from the Tektronix website. Waveforms can be easily created and sent to the AFG. Supported operating systems are Windows XP Professional, Windows 2000, Windows 98/ME, Windows NT and Windows 7 (32 bit only). PC requirements are Pentium III 800 MHz and higher, 256 MB RAM, 300 MB-free hard disk, Microsoft Internet Explorer 5.01 and higher, .NET Framework 1.1 Redistributable 800 X 600-display resolution.
With this software installed in the computer, you can create waveforms from standard waveform templates, modify and transform waveforms to test devices of interest, directly import waveforms from Tektronix oscilloscopes, send waveforms to AWG and AFG instruments directly from ArbExpress or MATLAB and perform math operations on waveforms.
These elements comprise the operator’s interface:
• Menu bar: When the user selects a menu item, a dialog box is displayed or immediate action occurs.
• Toolbar: Buttons access many features with no need to go through menus.
• Shortcuts: Provide access to multiple functions.
• Status bar: Provides information about the application and waveform.
• Marker area: The user can toggle the display of markers via Display>Markers in the menu bar.
To create a new waveform in ArbExpress, in the computer click File>Blank sheet. A new window with X-axis displays. The waveform length is 1,024 points. To change this number, click on Properties. In the Standard Waveform dialog box, available standard waveforms can be created. Waveform and instrument type are selected in Settings. Use Vertical to set vertical settings and Horizontal to set horizontal settings. Select Preview to see the waveform.
Other ways to create a waveform are to use the Equation Editor, waveform Math, or to remotely control the AFG. Equation Editor provides sample equations that can be directly used or modified. From the Command List, select commands, function, units or operations. Then the waveform can be seen in Preview after the equation is verified by clicking Compile.
A waveform library is available in Waveform Math from the Math menu. Select a math source. Calculations are shown in Resultant Waveform.
The external instrument can be controlled by means of AWG/AFG File Transfer and Control. Connected instruments are shown in Arb List. This pane appears only when an instrument is connected.
In the Communications menu, a dialog box appears when you select AWG/AFG File Transfer and Control. Then, settings can be selected for each connected instrument.