The oscillograph of the electronic measuring instrument uses six FAQs

The oscilloscope is still an indispensable tool on the current workbench, where six common problems based on oscilloscope users are collated to solve the doubts of laboratory researchers.

Q1: What are the requirements for the oscilloscope required for testing during high-speed serial testing? What are the most critical indicators?

A: Basically speaking, the bandwidth and sampling rate must meet the requirements of the serial signal. Next, it is necessary to examine whether it is a differential signal and an oscilloscope to analyze serial test functions, such as pattern triggering and decoding.

Q2: When measuring high-speed digital signals, is the oscilloscope's bandwidth more than 5 times the signal frequency? why?

A: Select the bandwidth of the oscilloscope, which is usually 2.5 times the speed of the measured signal or 5 times the maximum frequency of the signal, so you can see the 5th harmonic of the high-speed signal.

Q3: How does the bandwidth during the test affect the test result? What are the requirements for the bandwidth of the test instrument?

A: First, insufficient bandwidth will lose high-frequency harmonic components of the signal, leading to inaccuracies in time and amplitude testing. However, even if the oscilloscope with the same bandwidth shows different rise time, it is very important for the application to measure the error that occurs at the rising edge. In addition, in the data signal, the degree of opening of the eye diagram has a great influence. Because of this, the rise time indicator is very important for devices (oscilloscopes) that perform measurements in the time domain.

Q4: Is the bandwidth as high as possible?

A: As mentioned earlier, the rise time of currently widely used circuit boards, connectors, cables, and integrated modules is so limited that the loss of high-frequency components is severe after high-speed signals are transmitted. Many new third-generation standards (USB3.0, PCIE Gen3, 10G-KR) have taken this into account and require much lower bandwidth than before. Of course, there are some exceptions that require higher bandwidth. For example, the 100G Ethernet solution, which uses a complex modulation technique (DP-QPSK), requires four analog inputs and more than 20 GHz of bandwidth for analysis. Given these applications, Tektronix has announced that its oscilloscope with more than 30GHz bandwidth will be available later this year.

Q5: How can we increase the sensitivity of the test equipment?

A: Select the appropriate bandwidth, bandwidth is too large to increase noise, in the vertical settings, as far as possible to fill the signal screen, so as to make full use of the oscilloscope's AD number, you can use the average waveform, the appropriate probe bandwidth, select high resolution (Hi-res) acquisition mode and so on.

Q6: When debugging the system design, confirm the abnormal phenomenon and find out the operating conditions of the circuit in a short time. How to increase the chance of catching anomalies?

A: Use DPX technology and turn on infinite persistence. In a few seconds you can see abnormal signals that may not be visible for hours. This performance improves the chances of witnessing transient events in digital systems. These transient events include short pulses, glitches, and conversion errors.