Analysis of Frequently Asked Questions about Using Oscilloscopes
Q1: During high-speed serial testing, what are the requirements for the oscilloscope required for testing? Which indicators are the most critical? A: Basically, the bandwidth and sampling rate must meet the requirements of the serial signal. The next step is It is necessary to examine whether it is a differential signal and the analysis function of the oscilloscope for serial testing, such as triggering and decoding of pattern, etc.
Q2: When measuring high-speed digital signals, does the bandwidth of the oscilloscope have to be more than 5 times the signal frequency? Why? A: Choose the bandwidth of the oscilloscope, which is generally 2.5 times the rate of the signal being measured or 5 times the highest frequency of the signal. This allows you to see the 5th harmonic of the high-speed signal.
Q3: How does the bandwidth during testing affect the test results? What are the requirements for the bandwidth of the test instrument? A: First of all, insufficient bandwidth will lose the high-frequency harmonic components of the signal, resulting in inaccurate time and amplitude measurements. However, even though oscilloscopes with the same bandwidth will exhibit different rise times, it is critical for the application to measure the error that occurs on the rising edge. In addition, in the data signal, the opening of the eye diagram is also greatly affected. Because of this, rise time specifications are very important for devices that perform measurements in the time domain (oscilloscopes).
Q4: Is the higher the bandwidth, the better? A: As mentioned earlier, the rise time of currently widely used circuit boards, connectors, cables and integrated modules is very limited, so that high-frequency components are seriously lost 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 uses complex modulation technology (DP-QPSK) and requires four analog inputs and a bandwidth of more than 20GHz for analysis. With these applications in mind, Tektronix has announced that its oscilloscopes with bandwidths exceeding 30GHz will be available later this year.
Q5: How can we improve the sensitivity of the test instrument? A: Choose the appropriate bandwidth. Excessive bandwidth will increase the noise. In the vertical setting, try to let the signal fill the screen as much as possible to make full use of the AD digits of the oscilloscope. You can use waveform averaging. , appropriate probe bandwidth, select high-resolution (Hi-res) acquisition mode, etc.
Q6: When debugging the system design, how to confirm abnormal phenomena and clarify the operating conditions of the circuit in a short time? A: Use DPX technology and turn on infinite persistence, you can see it in a few seconds There are abnormal signals that may not be seen for several hours. This performance increases the chance of witnessing transient events that occur in digital systems, including short pulses, glitches, and conversion errors.
