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What Challenges Does Multi-Port Device Testing Face in the 5G Era?

With the advent of 5G, components are beginning to move toward more ports, more integration, and higher complexity.

From the device point of view, in the 2G/3G era, the mobile phone backplane basically sticks to a single component, including filters, power amplifiers, and duplexers. In the 5G era, devices are required to be smaller and smaller, and integration has become a new trend. For example, RF front-end modules integrate antenna switches, amplifiers, duplexers, filters, and the like.

From the perspective of antennas, in the 2G era, mobile phones basically use single-port antennas. In the 5G era, the reference to the millimeter wave band made the RF signal space loss very large. In order to improve this situation, the MIMO array antenna was used, and there were many ports. MIMO (Multiple-Input Multiple-Output) refers to the use of multiple transmit and receive antennas at the transmitting end and the receiving end respectively, so that signals are transmitted and received through multiple antennas at the transmitting end and the receiving end, thereby improving communication quality.

At the same time, more ports, more integrated, and more complex devices have brought many challenges to the test. At the Keysight Test Technology Symposium on October 17, Keysight Application Engineer LiMeng shared the 5G era. Problems and solutions for multi-port device testing.

Multi-port device testing faces many challenges

  • More and more parameters are being tested. For example, in the filter test, in the past, only the S parameter (that is, the scattering parameter is an important parameter in microwave transmission). Now, because of the integration trend, it is possible to measure FEMiD. The front-end module integrated with the duplexer needs to measure gain compression, third-order intermodulation, noise figure, etc. in addition to the S-parameter. Test, if it is a differential line, only need to measure the insertion loss or impedance, but now with the increase of transmission speed and the number of channels, in addition to measuring impedance and insertion loss, it is necessary to measure delay and crosstalk (including near string and far Strings, etc.), it can be seen that the measurement parameters increase sharply.
  • Test indicators are demanding. Because the multiport test is large, the test efficiency must be high. If the amount of testing increases dramatically and the test efficiency is the same, it takes a very long time to complete the test of the entire device.
  • High precision and good system stability. Multi-port devices impose very high requirements on test systems. If you want to test results with high accuracy and stability, you need to test more efficient test systems.

In the face of multi-port device testing, there are two more traditional test solutions on the market. One is to measure multiple times with a 2-port or 4-port network analyzer, and the other is based on a multi-port test system based on network analyzer and switch matrix. The former is less used and the latter is more common. The two test schemes have their own advantages and disadvantages.

Traditional test solutions have significant shortcomings

With a 2-port or 4-port network analyzer for multiple measurements, the advantage of this solution is that the test method is very simple and the instrument cost is low. There are many shortcomings. First, the test time is very long. Li Meng introduced that Keysight has done an experiment to let the engineers who are very skilled in instrument operation perform full parameter test on the 14-port device. It takes 50 minutes, which is for the production line. In terms of R&D, it takes too long. Second, the test process is very complicated. To test the N-port device with a 2-port network analyzer, N port devices need to be combined and measured, that is, N is required to be measured. N-1)/2 times; the third is to avoid crosstalk. When measuring the parameters of these two ports, other ports need to be connected to the load.

Based on a network analyzer and switch matrix multi-port test system, this solution uses a two-port network analyzer to measure the N-port device, and build a switch matrix between the network analyzer and the device, so that network analysis can be performed. The two ports of the instrument are cut to N ports through the switch. When testing, only the N ports of the test socket are connected with the object to be tested.

The advantage is that all ports can be connected at once, without changing the connection, and at a lower cost for dynamic range and accuracy requirements. There are many disadvantages, one is that the system dynamic range is down; the second is that the system accuracy and stability are not high; the third is the test speed is just so so, after adding the switch box, it takes 12 minutes to test a 14-port device, although compared with the first solution Although the time is much shorter, it is still too long for R&D and production lines.

What is the system dynamic range? The system dynamic range refers to the difference between the maximum output power of the network analyzer port and the port noise floor. The system index is usually defined under 10 Hz IFBW (intermediate frequency bandwidth). For every 10 times increase in IFBW, the dynamic range is reduced by 10 dB. For example, if the maximum output of the port is 5dBm and the dry bottom is -115dBm, the dynamic range of the system is 120dB (1FBW=10Hz). When 1FBW=1kHz, the dynamic range is 100dB.

After the switch box is added, the system dynamic range is affected. First, the internal insertion loss of the switch matrix will reduce the dynamic range, because the switch box has insertion loss, such as a network analyzer, which can output 10dBm signal. After the switch box is affected by the insertion loss, the power reaching the measured object will be Smaller, no longer 10dB; Second, switch isolation will limit the dynamic range of the system; third, in order to achieve the same dynamic range, you need to set a smaller IFBW (IF bandwidth), the test speed will be slower.

After the switch box is added, the system temperature stability and accuracy are not high. First look at temperature stability. For network analyzers, temperature stability is a very important indicator. What is temperature stability? To put it simply, the result of this time measurement is not the same as the result measured after two hours. This is that the stability is not good, that is, there is temperature drift. LiMeng pointed out that the network analyzer is composed of various active devices. The whole network analyzer system will give a temperature stability index when it comes out. Generally, the temperature drift of this temperature stability is very small, and the switch box is added. After that, the temperature drift of the temperature stability is obvious, that is, the same measured object, the result of the measurement is very different from the result measured after two hours. Let’s look at the accuracy of the system, because between the network and the measured object, a segment of the circuit, that is, the switch box, is connected, and the original performance (matching, directivity) of the system will be deteriorated, resulting in poor accuracy.

Although these errors in the switch matrix can be eliminated by calibration, the process is extremely complex, in two cases, if the network and switch matrix are provided by the same manufacturer and support multi-port calibration, such as Keysight PNA+ multi-port test bench, calibration measurement The process is relatively simple. In most cases, the switch matrix calibration measurement is complex and time consuming, and requires programming control. For example, when calibration, it is necessary to cut two port calibrations, save the calibration data, cut to the next port calibration, save the calibration data, and repeat N. (N-1)/2 times. After the measurement is completed, you need to cut two ports, call the calibration measurement, and then cut to the next two ports to call the calibration measurement.

After adding the switch box, it has an impact on the test speed of the entire system. As mentioned above, using only one two-port network, it takes 50 minutes to measure a 14-port device. After adding the switch box, the measurement speed drops to 12 minutes. Although the duration is greatly reduced, the system is not saved. The time of the data, but the time to manually screw the connection. The ability to process data is still dependent on the network, such as the two-port network, plus a multi-port switch box, but in fact the network receiving channel is still two channels of the network.

The network analyzer has an important parameter that affects the test speed, called the number of scans of the meter. Li Meng said that only the receiver that increases the ability to process data through the network analyzer can increase the speed of processing data. For example, to deal with an 8-port device, 2-port network split + switch box, requires 56 scans; 4-port net split + switch box, requires 24 scans; true 8-port network score, requires 8 scans, also It is the true meaning of the 8-port network, and all the parameters can be removed with 8 scans.

It can be seen that after the switch box is added, although the number of channels of the hardware can be achieved, the test accuracy, temperature stability, dynamic range, speed measurement speed, calibration complexity, etc. of the whole system will have a bad influence.

Therefore, for multi-port devices, only network analyzers with truly multi-port receivers provide the best system performance.

Conlusion

Compared with 4G, the 5G era has changed in many aspects. These changes mean that the related technology faces a comprehensive innovation, such as test technology. In the 5G era, a test solution with higher integration and flexibility is needed. In response to test challenges brought about by device integration, these challenges have also become important opportunities for test companies to win the market.

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