5G device and chip testing experience

From the beginning, the 5G communication system put forward the slogan of faster, higher and stronger (hey, isn’t this the Olympic motto?), from 1G to 5G and even to the future communication system, designers are adhering to this Ideal to design and upgrade communication systems from generation to generation.


The more powerful data communication capabilities of 5G and the design goals of richer connection scenarios, such as home theater, 4K or even 8K high-definition movies, VR, telemedicine, car networking and other emerging applications have been brain-inspired, imagine YY (for mass users) "Brainwashing" is very necessary, after all, the future investment depends on these people to recover).
To meet these design goals, how can there be no innovation? As a result, new technology terms such as Massive MIMO and millimeter wave became hot search terms for a while. But some people say that when 3GPP decided to continue to use OFDM technology for 5G NR, compared with 4G, 5G actually has no disruptive technology, and millimeter wave has almost become the "new idea" of 5G.
According to the 3GPP 38.101 agreement, 5G NR mainly uses two frequency bands: FR1 and FR2: FR1 (450MHz-6GHz), which is commonly referred to as Sub 6GHz; FR2 (24.25GHz-52.6GHz), which is commonly referred to as 5G mm Wave frequency band. The upcoming evolution on FR1 is considered by many to be the evolution of the current 4G system, and the expansion of millimeter waves is the new point and difficulty of the current 5G communication system, because even the technology of Massive MIMO is actually more It is to supplement the defects of the millimeter wave frequency band itself.
In the United States, the current major operators are still focusing on the development of millimeter wave 5G to supplement user access in remote areas. In China, although the priority is to deploy and develop Sub 6GHz 5G systems, by 2019, when it is about to be commercialized, operators have begun to gradually project their vision to the millimeter wave frequency band to achieve the powerful indicators of 5G communication systems.
No, not long ago, the Ministry of Industry and Information Technology has issued a millimeter wave license for China Mobile Hong Kong with a frequency band between 26GHz-28GHz. In addition, Hong Kong Telecom and SmarTone have also obtained 400MHz bandwidth in this frequency band.
01
What is millimeter wave
Millimeter Wave: Electromagnetic waves with a wavelength of 1-10mm are called millimeter waves. They are in the wavelength range where microwaves and far-infrared waves overlap, so they have the characteristics of both waves. The theory and technology of millimeter waves are the extension of microwaves to high frequencies and the extension of light waves to low frequencies.
02
Why extend to millimeter wave
Simply put, applications drive demand. Many years ago, wireless communication applications were not as crowded and prosperous as they are now. The frequency spectrum within 30GHz is sufficient for various applications, and the mobile communication system we are familiar with is basically concentrated on the high-quality frequency spectrum below 6GHz. However, after years of development, the high-quality spectrum resources within 6GHz can hardly squeeze anything. No matter what the toss (eliminate past applications, use cognitive radio technology to reuse spectrum, etc.), the spectrum resources of mobile communication systems are in short supply and conflicts. It is still a serious problem. Now to develop a new 5G system, it is enough for some operators to free up a small amount of spectrum resources in the 2G era. Until one day, someone suddenly discovered that there is still a large millimeter wave frequency band! The millimeter wave frequency band is like an undeveloped virgin land, a new continent, providing a large number of available spectrum resources for mobile users and operators.
03
The advantages of millimeter wave
Advantage 1
Great bandwidth. It is generally considered that the millimeter wave frequency range is 26.5GHz-300GHz, and the bandwidth is as high as 273.5GHz, which is more than 10 times the full bandwidth from DC to microwave. Even considering atmospheric absorption factors, a large part of the bandwidth of the millimeter wave band is not suitable for "living", making the millimeter wave band only have four main windows available, but the total bandwidth of these four windows can reach 135 GHz.
Advantage 2
The beam is narrow. Under the same antenna size, the beam of millimeter wave is much narrower than that of microwave. For example, a 12cm antenna has a beam width of 18 degrees at 9.4 GHz and a beam width of only 1.8 degrees at 94 GHz. Therefore, millimeter waves are often used to distinguish closer small targets or observe the details of targets more clearly.
Advantage 3
Compared with laser, propagation is much less affected by climate, so it can be considered to have all-weather characteristics.
Advantage 4
Compared with microwave, the size of millimeter wave components is much smaller. Therefore it is easier to make smaller models.
04
Such a large new continent, why do I remember to move to it now?
Although the millimeter wave frequency band has the above advantages, there are many difficulties in applying it to mobile communication systems:
Difficulty 1
The transmission distance of millimeter waves is really limited, and it is not easy to use it for large-scale coverage, and the cost of high-density deployment is also quite high. This is also a headache for many operators at present. The teacher taught us that the higher the frequency of radio waves, the shorter the propagation distance. Under ideal free-space propagation conditions, the loss of a 70GHz millimeter wave after 10 meters is as high as 89dB; and under non-ideal propagation conditions, the propagation loss is much greater. Therefore, the millimeter wave system must compensate for such a large propagation loss through various methods such as increasing the transmission power, increasing the antenna gain, and increasing the receiving sensitivity. Now the 5G communication system has introduced Massive MIMO large-scale antenna array technology, etc., which is also a way to move to the millimeter wave frequency band.
Difficulty 2
high cost. In the past, millimeter wave devices/chips have been used in the military field and cannot be commercialized on a large scale. But in recent years, through the use of SiGe, GaAs, GaN, InP and other materials combined with new production processes, chips working in the millimeter wave band have integrated transistors as small as tens or even a few nanometers, greatly reducing costs. It provides the possibility for the commercial application of millimeter waves.
05
To develop New World, are your devices/chips ready?
Although from the perspective of technical theory, the introduction of Massive MIMO and the mass production of high-power devices can solve the limitation of the limited millimeter wave propagation distance to a certain extent, but in order to achieve the predetermined index, all the millimeter wave links Both the device and the chip must work together perfectly. Each device/chip performs its own role, so that the entire system can finally reach the predetermined target.
In addition, under the increasingly stringent requirements of cost indicators, how much margin is left in the performance of the millimeter wave devices and chips you design and produce is also a question worth considering. Today, the editor will focus on the device/chip test for the 5G millimeter wave frequency band, and I will sort it out for you~
Typical millimeter wave chips/devices on 5G communication links are as follows: amplifiers, filters, mixers, transmission lines, antennas, etc. For this series of millimeter wave devices/components, we can summarize a series of general test requirements, as follows:

In response to the above test requirements, Keysight's powerful network analyzer single-unit frequency covers 67GHz, providing a series of test capabilities such as S-parameters, gain compression, intermodulation testing, pulse excitation testing, etc. There is no pressure, and it is a real millimeter wave Device/component integrated test system. Combined with an external spread-spectrum head, it can also provide test expansion capabilities in the 1100GHz frequency band.
General index test
On Wafer test + full parameter test of 5G millimeter wave components/devices
DUT size is small, need to cooperate with probe station and instrument for DUT measurement
DUT test port connection times are limited, and multi-parameter connection test can be performed
Calibration is more difficult, time-consuming and efficiency is affected, the stability of the meter must be good, and multi-channel calibration can be done at the same time!
DUT is not packaged, heat dissipation and shielding must be considered, so impulse test method is used
All the above On Wafer test requirements, Keysight's PNA network analyzer, one meter, all meet! For non-wafer-level full-parameter tests, our PNA can properly meet your test needs. The figure below is the connection diagram and calibration steps for our noise figure calibration in the On Wafer test~

The following is a typical configuration of our PNA-X N5290/91A
▼▼▼
Want to learn more about On Wafer test and full parameter test?
(noise figure calibration, power calibration, multi-channel calibration,
IDM test, gain compression test, pulse measurement, etc.)
Scanning test diagram and step analysis
Scan the QR code to get the test diagram and step analysis!
Of course, for amplifiers and other chips/devices, in addition to general test indicators, it is often necessary to test system-level amplification performance. Therefore, below we will also introduce system-level test solutions such as millimeter wave amplifier chips.
System index test
As mentioned earlier, since 5G millimeter wave and ultra-wideband amplifiers are still in their infancy, in order to verify and ensure that new power amplifiers can meet the requirements of 5G wireless transmission, both device manufacturers and base station system manufacturers need to re-debug and final system testing A large number of RF tests are carried out on the products at this stage. This aspect includes the above-mentioned network analyzer-based index tests such as de-gain and noise systems. The second type is the vector EVM and the vector EVM required for 5G broadband modulation signals according to the wireless communication system standards. ACLR adjacent channel leakage ratio and other tests.
Through a large number of experiments, we found that the EVM test for 5G millimeter wave and ultra-wideband PA is very different from the traditional 3G and 4G. The main reason is that millimeter wave and ultra-wideband conditions require the test platform composed of meters and accessories. Greatly improve, the distortion and error introduced by the test platform will seriously affect the final test result.
Uncalibrated UWB modulation signal example
The figure above is an example of a 5G modulated signal output using the Keysight M8190A+E8267D vector signal source (a 5G millimeter wave and ultra-wideband prototype platform created earlier in 2015). The bandwidth is 4GHz, and the data transmission rate of the physical layer modulation has reached 10- 20Gbps was the bandwidth modulation signal generated by the industry through meters at that time. But as you can see from Figure 1, the amplitude of different frequency components in the entire 4GHz range fluctuates greatly, and the frequency components far from the center frequency attenuate greatly, showing obvious amplitude unevenness. These attenuated frequency components will reduce the signal-to-noise ratio of the sub-carrier where they are located, and reduce the EVM. If this kind of signal is used for the radio frequency test of PA or base station, it will seriously affect the accuracy of EVM test.
Therefore, a very critical point in the 5G millimeter wave and ultra-wideband PA RF testing is that the test platform itself must have broadband calibration capabilities to ensure that the distortion and errors introduced by all meters and accessories before testing the PA are achieved.
Wideband signal calibrated by Keysight system calibration software
The picture above is an example of a wideband signal calibrated by Keysight system calibration software. During calibration, the overall EVM of the signal source and the driving amplifier is controlled within 1%, so that when the PA chip under test is connected to the EVM test, a more ideal flow can be obtained.