The Tektronix AFG31000 Series Function Generator can be used in conjunction with an oscilloscope to display the generated signals in one or two analog channels on a large LCD. Alternately, the AFG has smaller waveform displays with reduced resolution, nonetheless adequate for demonstrating the functionality of this powerful instrument.
When initially powered up, the AFG displays a Home screen, with two large icons – Basic and Advanced. The AFG has a touch screen, so all you have to do is lightly touch either of the two icons. Beginning with the Basic mode, we see the two channel outputs displayed.
The purpose of the Basic mode is to display any of the 13 internal waveforms generated by the instrument. In addition to displaying them in the LCD, they are applied to the two channel outputs at the BNC ports at the bottom of the front panel. These outputs have to be turned on, and then they will convey the signals through attached BNC cables. They can be applied to an oscilloscope, for example, where the signals can be manipulated, combined in the Math mode, stored or exported to a computer.
Also, BNC breakout cables, terminating in wire leads or alligator clips, are available, so the AFG signals can be injected into electronic equipment under investigation or probed into components or printed circuit boards. The default signals, as seen in the tabs at the tops of the two channel displays, are Sine. Touching the tabs, drop-down menus display the twelve other available signals:
• Exponential Rise
• Exponential Decay
Any of these signals can be displayed and exported by touching the tabs in the drop-down menus. Identical or different signals are available in the AFG display or through the BNC cables. The other tab that appears in both channel displays relates to how the signals can be modified prior to display and export.
So far, we have been looking at the default, Continuous, which displays and exports the signals simply as generated within the AFG. In the continuous mode, five parameters as shown below the waveform drop-down menu can be set. The first, Frequency, is self-explanatory. It toggles to its reciprocal, Period. Either of these can be set by touching the value. When you do so, a number pad appears on the screen, and touching the keys or using the keypad at the right side of the front panel, values can be entered and the output is modified accordingly. Besides Frequency/Period, Amplitude, Offset and Units can be set. Touching the tab, the choices are listed in a drop-down menu:
When Modulation is touched, Modulation Type may be selected. The choices are AM, FM, PM and FSK. Of these choices, the AFG permits further selections. For example, when AM is selected, the choices are Internal and External.
Another mode is Sweep. This is often injected into equipment under investigation, and it is useful because it demonstrates how the equipment responds to a range of inputs, which can be injected into any stage, circuit or component. When Sweep is chosen, touching the window brings up an on-screen number pad, which can be used to quantify the sweep.
When burst is selected, the number of cycles can be chosen: one cycle, a specified number, an infinite number, or the burst can be gated. The burst can consist of any of the 12 AFG internal signals listed above, plus arbitrary, which refers to user-created signals.
Returning the AFG Basic mode to Sine and Continuous, which are defaults, we’ll return to the Home screen and touch Advanced mode. Advanced mode allows the user to create arbitrary waveforms and customize them. They go beyond the 12 internal waveforms created by and stored in the instrument. There is an unlimited
number of these arbitrary waveforms that can be created, and this number is multiplied by the vast number of parameter values that can be imposed by the user. There are endless variations. In the digital domain, pulse trains or data packets can be generated over a serial bus. Waveforms in the Sequencer can be organized in various ways, such as repeat, wait, jump, go to and triggering with events such as external trigger, manual trigger, times and SCPI commands.
Each point in an arbitrary waveform is output once in each cycle at the specified sampling rate, with no skips or repetitions.
The Advanced mode is useful when working with signals where jitter or noise may be a problem, such as serial bus simulation or I/Q modulation, or where small anomalies in large waveforms are to be simulated. In Advanced mode, the authentic details are displayed while jitter and phase noise are reduced and there is always the same number of samples in each cycle.
Advanced mode has four basic output modes – Sequence, Continuous, Triggered and Gated. You can open a saved waveform sequence by choosing Sequence. This provides greater flexibility when generating waveforms that have complex timing, which can be defined with as many as 256 steps, equating to 16 MB per channel total waveform length. It is possible to organize the steps as a loop, go to or triggered by jump or wait events.
In Continuous mode, the AFG31000 outputs a one-step waveform sequence repeatedly as long as it continues to run. When the AFG receives a trigger input, it produces one cycle of waveform output. When it is gated, the AFG outputs a one-step waveform sequence. It stops when a second effective gate signal is triggered.
The advanced mode outputs the waveform in accordance with the sequence table, including loop and conditional jump. In its output, the waveform is defined by the selected sequence. Multiple waveforms can be output in any specified order. The advanced output mode screen permits the user to choose from available waveforms, select Sequence to open a saved waveform sequence or to create and save a new waveform.
The advanced sequence list screen permits the user to open an existing waveform sequence, initiate a new single sequence, save a waveform or using Save As, create a new file name while retaining the old one.
The advanced waveform list permits the user to open an existing waveform, locate the waveform in the AFG memory, locate the waveform in a flash drive, locate the waveform in a memory location or delete waveforms from the waveform list.
The Advanced Setting Bar, based on a definition in the sequence table, outputs a sequence of waveforms. In the continuous mode, the AFG outputs a single waveform repeatedly when running. When the AFG receives a trigger input, one cycle of the waveform is output. After this one cycle, the AFG returns to its initial state and awaits another trigger output.
In the gated mode, the AFG outputs a single waveform sequence when a gate signal is received and stops when a second gate signal is received.
In the Advanced Setting Bar for channel 1/channel 2, Scale is the amplitude scaling based on offset in a sequence of waveforms on one channel. Offset is the average of the maximum and minimum voltage in a sequence of waveforms on a single channel after waveforms are dragged into the sequence table. The user can change the offset to adjust the average position.
The timing setting bar allows the user to set the sampling rate. The timer allows the user to set the timing for the signal generating function. The advanced table setting bar allows the user to repeat the signal-generation function until the Stop instruction occurs. The Wait event is an event that must occur before the waveform is generated. A Jump event triggers the AFG to go to a different step. A Jump address sets the Jump destination for a Jump event.
Go to moves to a specific step in the sequence after generating the waveform specified in a sequence element. On the sequence table the sequence mode can perform these actions:
Event selection, Wait or Jump. If Wait is on, the waveform output is suspended until a Wait event occurs.
Repeat defines how many times the waveform is repeated: one to one million or an infinite number.
If Jump is on, the current waveform is interrupted when a Jump event occurs, and the Sequencer immediately jumps to the Jump event.
Go to: Once the current waveform repetition is complete, the Sequencer goes to the next Go to address.
Note: In the AFG31000, there is a sharp bend in the learning curve between Basic and Advanced.