Technical Insights > Benchtop

How to Time Synchronize Multiple Function Generators Together

2018-12-21  |  8 min read 

Most basic bench function generators have only one or two output channels. In some cases, you may need more than two channels. Due to this need, many test engineers are forced to buy very expensive multichannel waveform generators. In this blog, we will look at how to easily time-synchronize multiple basic function generators together without the hassle of using external synchronizing trigger boxes or tedious programming. This mitigates the need to purchase expensive multichannel waveform generators.

Many applications require multichannel, time-synchronized waveforms. For example, some devices calibrate with synchronized pulses of varying pulse widths. You can easily simulate these signals using multiple basic function generators. Other applications could include simulating optocoupler decoder signals, multichannel Pulse Width Modulation (PWM) motor controllers, and so on.

How to synchronize two function generators

Today, we’re going to look at how to display four time-synchronized output waveforms using two 2-channel function generators (Keysight 33612As). For our test, we want to generate four 3 kHz pulse trains at 1Vpp. And we want the pulse widths of the four channels to start at 100 µs and increase by 10 µs for each channel. So, the fourth channel pulse width will be 130 µs.

The first thing to do is wire configure the rear of the two function generators, as shown in Figure 1. Make one of the function generator’s 10 MHz frequency timebase be the reference for the other function generator. Connect the 10 MHz clock out of the reference function generator to the 10 MHz clock in of the other function generator. (Note that you can fan out the reference clock up to four Trueform function generators).

Synchronize multiple function generators
Figure 1. Rear wire configurations on timebase and external trigger synchronization between two function generators.

Next thing to do is to connect the External Trigger out of the reference function generator to the Trigger in of the other function generator. That’s all that is needed for external wire configuration.

User interface system and waveform settings

Reference timebase oscillator and trigger setup

The next step is to set the second function generator’s reference oscillator to external. This ensures that your function generators both operate off from the same timebase.

Button presses: Select menu button, System > Instrument Setup > 10 MHz Ref Osc > Source > External.

Once that is done, you will see a green Ext Lock sign on the top right-hand side of your function generator, as shown in Figure 2.

Channel trigger setup on function generator
Figure 2. Second function generator’s reference oscillator and external trigger setup.

After setting up your reference oscillator, you will have to set up your trigger for both channels of your second function generator. The trigger tells the second function generator to start at the same time as the first function generator.

Button presses: Select Channel 1 output button and then press the Trigger button. Select Trigger Setup > Source > Ext (External). On the same screen menu level, select zero seconds delay and trigger slope on the rising ↑ edge. See Figure 2 on the external trigger menu.

On the first reference function generator, just set up the trigger for both channels to manual and zero delays.

Button presses: Set Channel 1 as the source of your trigger out and on the rising ↑edge. Select Trigger on Channel 1 > Trig Out Setup > Source > CH1. On the same menu level, select the trigger level and trigger out ↑edge.

Set up your pulse waveform signals for all your four channels (2 channels per instrument)

As mentioned earlier, we want to set up four 1 Vpp pulse trains that are 3 kHz in frequency, and the pulse widths should start at 100 µs and increase by 10 µs increments for every channel. (See Table 1 and Figure 3.)

Table of four pulse channel configuration setups
Table 1. Pulse waveform signals set up for four channels.

Pulse setup on 33600A function generator
Figure 3. Example pulse setup menu for all four channels.

Set up burst mode to time synchronize all four channels

At this point, if you look at all four channels on an oscilloscope, you will see the four pulse trains, but they are not time synchronized (Figure 4). All channels run independently; hence they are not initially synchronized.

Multi-Channels unsynchronized pulses
Figure 4. Multichannel outputs that are not time synchronized.

To time synchronize all four channels, use the Burst mode (Figure 5).

Button presses: Go to all 4 channels, Select Burst > N Cycle > # Cycle > Infinite.

Burst Mode setup
Figure 5. Burst mode setup menu on function generator.​

Turn on Burst for all four channels. You will be prompted by a blinking light on the Trigger button of your Channel 1 on your first function generator. Press the button twice, and instantly, you will see four channels of time-synchronized pulse trains (Figure 6).

Synchronized multi-channels
Figure 6. Time-synchronized, multichannel outputs

You will also notice that each pulse width is 10 µs longer than the previous channel. You have just walked through the hardware and front panel configurations to time synchronize four channels. Since you can fan out the 10 MHz reference clock to up to four Keysight’s Trueform function generators, you can have up to 8 time-synchronized channels.

Knowing how to set up time-synchronized multiple waveforms does not mean that you cannot be creative with your waveforms. Figure 7 gives you an example of simulating a 3-phase AC generator with three sinusoidal waveforms, 120° apart from one another.

3 phase AC generator
Figure 7. Simulated 3-phase AC generator 120° apart with multiple function generators.

Summary

In this blog, you’ve learned how to time synchronized at least two function generators together through some simple rear wire configurations, setting up one of the function generators as a reference, and use burst mode to trigger time synchronized multiple channels. I hope this blog is insightful for you. If you want to learn more on how to get the most out of your function generator, please download our eBook on “5 key tips for getting the most out of your waveform generator”.

For more information on Keysight’s Trueform function generator, please visit this URL: http://www.keysight.com/find/function-generators