The signal generator outputs two waveforms with different timings. The minimum timing interval

Continuing from last week’s article, in some tests we need two drive signals with inconsistent timing to control a switch tube, such as MOSFET or IGBT, and in some tests the interval between the two turn-on signals or turn-off signals is very important.

For example, in the double pulse test (DPT), when studying the current sharing problem of parallel power switch tubes, we need to control the driving signals of different switch tubes to arrive at different times, which involves the problem of the minimum timing interval between the two falling edges.

Figure 1 Minimum timing interval Tmin

We use the "arbitrary wave" function of the Tektronix signal generator we talked about last week to test the minimum time interval between two waveforms. According to last week's article, we set the period to 10us and the number of horizontal axis points to N=10000 points.

Figure 2 Settings of the “Arbitrary Wave” interface

After a simple calculation, it can be found that under this setting, the difference between each point is 1ns.

Figure 3 Coordinate setting with 10ns interval

We first set the falling edge difference of the two waveforms to ΔT = 10ns, and the coordinates are set as shown in Figure 3.

The output waveform observed using a 200MHz oscilloscope from Tektronix is ​​shown in Figure 4.

Figure 4 Signal generator and the falling edge of the oscilloscope itself

As shown in Figure 4, the fall delay caused by the signal generator and the oscilloscope itself is 6.6ns.

Figure 5 The timing interval differs by 10ns

From Figure 5, we can see that when we set the difference between the two falling edges to 10ns, the actual waveform timing observed by the oscilloscope differs by 10.2ns, which is within the allowable error range and is accurate.

Similarly, we tested the limit case under 1ns, as shown in Figure 6.

Figure 6: Timing interval difference of 1ns

It can be found that when we set the timing difference between the two channel waveforms of the signal generator to 1ns, the oscilloscope observes that the actual output timing interval is about 1ns. It can be seen that using Tektronix's signal generator to set the dual-channel output timing interval to around 1ns is still relatively accurate.

Figure 7 Voltage overshoot caused by measurement method

Finally, it should be noted that, as can be observed from Figure 7, the voltage overshoot caused by the measurement method is relatively large, so when we test the circuit, we need to pay attention to the parasitic inductance of the test loop.

END