Testing and analysis of probe performance parameters

During the test, we used the N5244A PNA-X vector network analyzer with a frequency range of 40GHz and the PLTS physical layer analysis software to conduct a comprehensive test and analysis of the performance of the probe, which can be used as a basis for judging the quality of the probe. First, the S11 parameters of the probe after short circuit were tested using PNAX and electronic calibration components. Then, the PLTS analysis software and AFR calibration technology were used to obtain the probe's four S parameters, time domain impedance parameters, and response time parameters. The following are the characteristic curves of the two probes obtained after testing probe No. 1 and probe No. 2 respectively, and then converted using the PLTS software.

1. Frequency domain reflection characteristics of the probe. Figure 1 is the S11 of needle No. 1, and Figure 2 is the S11 of needle No. 2.

Figure 2: S11 of needle No. 2

From the S11 curves of the two probes, we can get the following results: the return loss of probe 1 is better than -20dB in the frequency range from 10 MHz to 30GHz, and the typical value is -24dB. For probe 2, when the frequency is higher than 15GHz, the return loss is worse than -20dB, and the typical value can be obtained from the curve: at 24GHz, it is -15.07dB. This shows that the operating frequency of probe 1 can reach 30GHz, while when the operating frequency of probe 2 is higher than 15GHz, the reflection will obviously affect the consistency of impedance test.

2. Analysis of the time domain impedance characteristics of the probe. Figure 3 is the time domain impedance of needle No. 1, and Figure 4 is the time domain impedance of needle No. 2.

Figure 4. Time domain impedance parameters of pin 2

Using PLTS software, the frequency domain S parameters of the device can be converted into impedance parameters in the time domain, thereby obtaining the impedance parameters of the device in the signal propagation path. From the time domain impedance curves of the two probes, it can be measured that at 0.21ns, needle 2 has an impedance mutation higher than needle 1. After judgment, the location of the impedance mutation point is at the transition connection between the probe 2.92mm coaxial connector and the probe body. This impedance mutation point indicates that the impedance continuity at the transition of needle 2 is worse than that of needle 1, and the impedance characteristics at other locations are similar to those of needle 1. The preliminary judgment is that the impedance mutation at the connection of needle 2 affects the working frequency range of the probe.

3. Analysis of probe response time characteristics: Figure 5 shows the response time parameters of probe No. 1, and Figure 6 shows the response time parameters of probe No. 2.

Figure 6. Response time parameters of needle No. 2

The probe response time characteristic test uses the time domain stimulus signal with a rising edge of 16ps provided by the test system to stimulate the probe and test the rising edge time after the probe responds. The test function is completed by the PLTS software. From the test parameters, it can be obtained that after passing through the probe, the No. 1 needle delays the 16ps system rise time to 28ps, and the No. 2 needle delays the 16ps system rise time to 30ps.

Through the above test and analysis of the probe performance, we know that the use of PNAX and PLTS physical layer analysis software can test the time domain impedance of the device, so as to analyze the internal structural characteristics of the device. At the same time, the S parameters can be used to obtain the frequency domain characteristics of the device and its operating frequency range. The PLTS software can also further obtain the response characteristics of the device to the signal rise time. In addition, the uniqueness of the AFR technology of the PLTS software is that it can test and obtain the full S parameters of a single-port connection device (such as a probe), so that its internal structural impedance, frequency domain and time domain parameters can be tested and analyzed in detail.

Note: The above test is a typical test of the probe performance parameters. The test results will be affected by multiple factors, such as the short-circuit connection method of the probe, the type of adapter, etc., which will affect the accuracy of the test results. The above test results and analysis are for reference only.