Electronic – Bandwidth of an oscilloscope with differential probe

bandwidthdifferentialoscilloscope

I am planning to buy Rigol MSO5204 scope with a bandwidth of 200 MHz. I need to measure the timing difference between 2 (or more) signals of up to +/- 7 ns. Since this scope has 8 GS/s sampling rate, I figured it will suffice my needs. Also, a cheaper model in the line Rigol MSO5074 offers the same features but, with a bandwidth of 70 MHz only. My signal frequencies are less than 10 MHz. The decrease in the bandwidth will increase the Rise time (from 1.75 ns to 5 ns) of the scope. My questions are:

  1. From experience, can anyone tell if 7 ns timing difference between signals can be captured if the rise time of the scope is 5 ns vs 1.75 ns?
  2. Is it worth spending extra money for a better rise time?
  3. I will be using a differential probe and most of the differential probes that I came across are 25-50 MHz bandwidth range. Could adding a differential probe with BW of 25 MHz affect the above timing measurements given that the signal frequencies are going to be less than 10 MHz?

Best Answer

From experience, can anyone tell if 7 ns timing difference between signals can be captured if the rise time of the scope is 5 ns vs 1.75 ns?

For a signal with a 7 ns rise time a 5ns scope would see 1.4pts during that time
The same signal with a scope that samples 1.75ns would see 4pts. How many points to do you need to see?

Question 2 is a matter of opinion, it's a trade-off of money vs need.

I will be using a differential probe and most of the differential probes that I came across are 25-50 MHz bandwidth range. Could adding a differential probe with BW of 25 MHz affect the above timing measurements given that the signal frequencies are going to be less than 10 MHz?

A 70Mhz scope with a 25Mhz probe will only be able to 'see' signals at 25Mhz. For example, if you had a 50Mhz sine wave with a 25Mhz probe, it would probably be so attenuated you wouldn't be able to tell it's there. The oscilloscope would be more than happy to display points at 70Mhz. So you are limited by the probe. A slower probe is like having a filter on the scope.

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