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.
There are many applications that 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 33612A). 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 off 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).
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.
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. This 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 4 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.)
|Frequency||3 kHz||3 kHz||3 kHz||3 kHz|
|Amplitude||1 Vpp||1 Vpp||1 Vpp||1 Vpp|
|Offset||0.00 V||0.00 V||0.00 V||0.00 V|
|Pulse Width||100 µs||110 µs||120 µs||130 µs|
Table 1. Pulse waveform signals set up for 4 channels.
Figure 3. Example pulse setup menu for all 4 channels.
Set up burst mode to time synchronize all 4 channels
At this point, if you look at all 4 channels on an oscilloscope, you will see the 4 pulse trains, but they are not time synchronized (Figure 4). All channels run independently, hence they are not initially synchronized.
To time synchronize all 4 channels, use the Burst mode (Figure 5).
Button presses: Go to all 4 channels, Select "Burst" > "N Cycle" > "# Cycle" > "Infinite".
Figure 5. Burst mode setup menu on function generator.
Turn on Burst for all 4 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 4 channels of time-synchronized pulse trains (Figure 6).
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 4 channels. Since you can fan out the 10 MHz reference clock to up to four Keysight 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 3 sinusoidal waveforms, 120° apart from one another.
To learn more about phase, frequency, and amplitude signal coupling, please read the Effortlessly Couple or Synchronize Two Signals on a Waveform Generator application brief. I invite you to like and share if you have found this blog helpful. Thanks for reading.