Specific operating steps for oscilloscope probes

　　An oscilloscope is a very common electronic measuring instrument that can convert electronic signals that are invisible to the human eye into visible images. The oscilloscope probe is particularly important for the accuracy and accuracy of the measurement results. It is an electronic component that connects the circuit under test and the oscilloscope input. Next, I will explain in detail how to operate the oscilloscope probe and calibrate the oscilloscope probe.

　　1. How to use oscilloscope probes
　　The impedance matching part of the probe should be adjusted before use. There is usually an adjustable capacitor at the end of the probe close to the oscilloscope, and some probes also have an adjustable capacitor at the end close to the probe. They are used to adjust the impedance matching of oscilloscope probes. If the characteristic impedance does not match, the measured waveform may be distorted. The operation method of adjusting the oscilloscope probe is as follows:
　　How to use the oscilloscope probe
　　1. Set the input option of the oscilloscope on GND, and then adjust the Y-axis offset knob to make the scan line appear in the center of the oscilloscope. Check whether the scan line at this time is horizontal (that is, whether it overlaps with the horizontal center line of the oscilloscope). If not, you need to adjust the horizontal equalization knob (generally, the analog oscilloscope has this adjustment terminal. In the small hole, you must Use a screwdriver to insert it and adjust it (no adjustment is required for the data oscilloscope).
　　2. Then connect the input selection of the oscilloscope to the DC coupling, and connect the oscilloscope probe to the test signal input and output terminals of the oscilloscope (generally, oscilloscopes have this output terminal, usually a 1KHz sine wave signal), Then adjust the scan time knob so that the waveform can display about 2 cycles of time. Adjust the Y-axis gain value knob so that the peak-to-maximum value of the waveform is around 1/2 of the total width of the display screen. Then observe the upper and lower sides of the waveform to see if it is level. If overshoot, skew, etc. occur, it means that the matching capacitor on the probe needs to be adjusted. Use a small screwdriver to adjust it until the wave patterns on the left and right sides are level and there is no overshoot. Of course, it may be that due to the quality of the oscilloscope probe, the adjustment may not be able to achieve a completely lossless effect. At this time, the only way to achieve the best effect is to adjust it.

　　2. Oscilloscope probe calibration
　　There are usually three calibration methods for oscilloscope probes:
　　1. DC gain and offset calibration.
　　DC calibration is the most commonly used calibration method for oscilloscopes. It compares the calibration signal derivation (standard DC voltage) and the actual test of the oscilloscope. The working voltage of the calibration data signal is used to adjust the gain value of the probe to test the DC voltage and its offset error. The whole process of DC calibration is to determine the values ​​of linear equation y=mxb index m and b. The DC calibration of the probe needs to be carried out at least once a year, and more often it will be done every few months or even once a day.
　　2. AC calibration:
　　A high-performance oscilloscope for testing fast data signals. Because the network bandwidth is very wide, it is difficult to ensure that the in-band amplitude and phase frequency responses are absolutely flat. In order to improve the measurement accuracy, it is necessary to calibrate the phase-frequency characteristics within the band so that the oscilloscope and probe test system have consistent frequency and phase-frequency characteristics in different frequency bands within the entire network bandwidth. DC calibration cannot adjust phase-frequency characteristics. The probe AC ​​calibration method is to use a network analyzer to test the S parameters of the digital power amplifier probe amplifier, and adjust the phase-frequency characteristics of the probe based on the loss of each frequency band tested. The oscilloscope manufacturer will test the S parameters of each probe amplifier when shipping and store them in the memory chip of the probe's internal structure. When the customer uses the probe, the oscilloscope loads the probe S parameters for AC calibration.
　　3. On-site AC calibration by the user
　　. The above probe AC ​​calibration process uses the fixed S parameters provided by the manufacturer at the factory for calibration, which cannot take into account the wear and tear of the probe connection accessories under different circumstances. In fact, customers' application conditions vary greatly, such as different probe connection front lengths. For oscilloscopes and probes with network bandwidths of tens of GHz, it is very necessary to perform AC calibration based on customer application conditions and test accessories.
　　The process of using a network analyzer to test S parameters is complicated and uncomfortable to use in the local environment. At present, Agilent's indium phosphide-based oscilloscope itself can provide a rising edge signal of less than 15ps as a calibration source. Because the rapid rising edge contains sufficient high-frequency components, it is effective and efficient to use fast-edge signals as a calibration source. feasible.