Oscilloscope Differential Probe Delay Measurement

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Oscilloscope Differential Probe Delay Measurement [Copy link]

When measuring with an oscilloscope, choosing the right differential probe can improve the accuracy of the test. When choosing a differential probe, make sure it has sufficient bandwidth for the application measurement, at least its bandwidth value should not be less than the bandwidth value of the oscilloscope. Secondly, make sure its maximum differential voltage is greater than the required measurement range and the common mode rejection ratio meets the test requirements.

In addition, it is also very important to use the appropriate line length for the differential probe. If the wire is too long, it may increase the capacitance and increase the propagation delay. Usually, the propagation delay of the probe is mostly caused by the line length. If different probes (such as voltage probes and current probes for power measurement) are used to measure the same test point simultaneously, the propagation delay has no effect on the measurement of most signals, but it may cause deviations in the measurement results of some high-speed signals. For example, when measuring the phase (time difference) between two different signals, a probe with the same propagation delay should also be used for measurement.

Today we will teach you how to measure the propagation delay of a differential probe.

First, we use a signal generator to generate a signal with a frequency of 1KHz and an amplitude of 20V peak-to-peak. Then, connect a BNC multi-turn cable to the oscilloscope's channel 2, and then input the signal generated by the signal generator into the oscilloscope's channel 2. Finally, connect a differential probe to the oscilloscope's channel 1, and connect the signal output from channel 2, that is, also connect the waveform of the signal generator.

In this way, channel one inputs the signal of the signal generator through the differential probe, while channel two directly connects to the signal of the signal generator.

Then we adjust the vertical position and time base of the oscilloscope so that the waveforms of channel 1 and channel 2 are in the appropriate display position. Then we turn on the cursor and move the cursor to the intersection of each channel signal and its zero point line, so that the cursor can be guaranteed to be at the same position at the intersection of channel 1 and channel 2. Then at this time, the difference of the cursor is the propagation delay of the differential probe. As shown in the figure below, the yellow channel 1 (differential probe) lags behind the blue channel 2 (directly connected signal source) because the differential probe channel 1 has a certain delay relative to the direct-connected signal source of channel 2.

In this way, the propagation delay of the differential probe can be roughly measured. We used the same method to test the Microsignal high-voltage differential probes DP5013, DP10007, DP10013, and DP20003 (the input line length of the four high-voltage differential probes is about 45cm, and the output line length is about 90cm).

The propagation delay of DP5013 is about 11.1ns

The propagation delay of DP10007 is about 12.8ns

The propagation delay of DP10013 is about 11.1ns

The propagation delay of DP20003 is about 10.9ns

Jacktang

This is a good way to generate differential signals.

We use a signal generator to generate a signal with a frequency of 1KHz and an amplitude of 20V peak-to-peak. Then connect a BNC multi-turn cable to the oscilloscope's channel 2, and then input the signal generated by the signal generator into the oscilloscope's channel 2. Finally, connect a differential probe to the oscilloscope's channel 1, and connect the signal output from channel 2, that is, also connect the waveform of the signal generator.