| Wireless testing technology is currently at an unprecedented crossroads, mainly due to the following factors: ● New wireless communication standards ◆ WiMax (802.16) ◆ UWB (Ultra-wideband) ◆ 802.11n ● Integrated technology ◆ RF transceiver integrated with ADC/DAC devices ● High-speed serial bus ◆ PCIe (PCI Express) ● Higher testing frequency Some or all of the above new technology developments will have a huge impact on wireless device testing. These technological impacts will not only affect the testing of complex devices, such as those integrating high-speed digital buses and RF channels, but also relatively simple ones, such as independent RF channel testing. New wireless communication standards Bandwidth
Most new wireless standards emerge with the need to increase bandwidth to meet the demands of higher data transmission. Figure 1 shows the relationship between the adoption time and bandwidth of wireless communication standards.
Since the early 1990s, the bandwidth of wireless channels has been increasing dramatically. The success of the WLAN (802.11) standard has further increased the trend of bandwidth increase, so test companies have to strive to keep their equipment advanced. In recent years, the implementation of the UWB standard has brought extremely severe challenges to test technology. WLAN standards generally have a bandwidth of less than 100MHz, so test technology does not require special methods to deal with it. However, the bandwidth of the UWB standard can reach 500MHz, which will have a great impact on the design of testers. The tester design method for testing RF receivers at this bandwidth is very different from other wireless test systems. Generally speaking, the sampling accuracy of UWB (8 to 10 bits) is lower than the traditional RF sampling accuracy (12 to 14 bits). Therefore, a special solution needs to be designed to test the UWB protocol. As semiconductor devices become more integrated, the number of RF channels in wireless devices is also increasing. Three to five years ago, CDMA devices first had more RF channels because they integrated GPS and analog cellular parts. Newer mobile phone chips integrate many communication channels
such as W-CDMA, GSM and GPS. Therefore, it is not uncommon to have 11 RF channels on a chip. WLAN (802.11) protocols are also driving the increase in the number of RF channels. Chips with MIMO technology in these systems can easily reach 10 RF channels. This is partly because in order to support the 802.11 a/b/g standards, the device must support multiple antennas and multiple communication frequencies (2.4 or 5.2GHz). In addition to the increasing number of RF channels, the IQ baseband channels of these transceiver devices are also increasing. It is not uncommon to have 3 pairs of TX I/Q channels and 2 pairs of RX I/Q channels. This will further increase the requirements for the baseband mixed signal test capabilities of the test system. Digital and analog separation technology In the past 5 to 8 years, the zero-IF transceiver method has dominated the chipset structure of GSM and WLAN wireless systems. The CDMA system has not changed fundamentally in structure except that it has to meet the full-duplex isolation requirements on the RX and TX chips. The structure is shown in Figure 2:
In the traditional zero-IF transceiver architecture, the baseband interface is composed of analog I/Q differential signals. The typical frequency of these signals is 100KHz (GSM) to 20MHz (WLAN). The test of these signals can be implemented on most test platforms using traditional mixed signal instruments. Although these analog I/Q interfaces have been used in wireless communications for many years, the need for more general-purpose RF front ends to handle multiple wireless protocols (GSM, EDGE, cdma2000, WLAN) has driven the wireless semiconductor industry to find a simpler and more flexible solution. The general trend in the industry is shown in Figure 3.
As can be seen in Figure 3, the ADC and DAC parts have been moved from the baseband processor to the RF transceiver. This has many benefits: ● Can simplify all digital interfaces and back-end designs ● The analog and digital parts are completely separated - the RF XCVR part is a pure analog and RF part, while the baseband processor is a pure digital part. This can simplify the manufacturing process and enable the baseband processing part to keep up with Moore's Law. The scale of the RF and analog parts cannot increase year-on-year with the geometric size of the process, so the life cycles of the two different technologies can be completely separated. ● Universal XCVR can be designed - Since the baseband interface is now purely digital, the RF transceiver can be designed for different frequencies and standards. The baseband processor can process the sampled analog signal according to different standards. This makes it possible to have a completely universal mobile phone. Although this approach has greatly benefited the mobile phone manufacturing industry, it has caused a lot of trouble for test engineers. The digital speed of these interfaces can range from 50Mb/s to 400Mb/s. 50Mb/s is not a problem for most ATE, but 400Mb/s is a huge challenge for today's ATE solutions. Moreover, even if the interface speed issue does not bother us, although the tester can handle high-speed testing, test time will also be another huge challenge. In these tests, the data is not purely digital, but is sampled from analog signals. In other words, traditional signal processing methods need to be used to process this data. Most digital pins can capture data and then pass it to the tester's CPU, but this is far from the best solution, because under the tight product price conditions, these hundreds of milliseconds of test time may be the culprit for product failure. The new tester architecture must be able to efficiently handle the testing of this interface. High-speed bus testing For many years, many industry observers have predicted that high-speed serial bus + RF technology will emerge. Today, a chipset integrating RF wireless LAN technology and PCI express bus is finally available. The bus standard of PC has also changed from the old PCI bus to the PCIe bus. Any peripheral device developed based on the PC environment must comply with the PCIe bus standard. At least two major WLAN suppliers can provide single-chip PCIe bus WLAN solutions. This requires the test platform to have 2.5Gbps and 3.2Gbps digital interface bus (usually one lane per chip) testing and standard RF testing capabilities. Note: One lane is a serial TX and RX differential pair. Not all current ATEs have this test capability, and it is likely to eliminate a large number of test platforms. Anyone who wants to commit to the WLAN test market must take this issue seriously. Higher testing frequency The final challenge for RF testing is higher RF frequencies. 6 GHz has been the frequency dividing point between mainstream commercial applications and military application technologies for more than a decade, but now this dividing point is beginning to change. There are 3 basic applications that require higher frequency ranges: ● Ultra Wide Band (UWB) – up to 0.6 GHz ● WiMax (802.16d) – up to 11 GHz ● Mobile phone harmonic components – >10 GHz As for UWB, the Federal Communications Commission of the United States has allocated it a frequency band of 10.6 GHz, as shown in Figure 4.
Although no device has used this frequency band yet, it is certain that high-speed data transmission systems will develop in the direction of high frequencies.The frequency band allocated by WiMAx is 11 GHz. Most of the devices today are within the 3.5 GHz area, but in order to reduce interference, high frequencies must also be developed. Finally, as wireless semiconductor manufacturers integrate more functions into a single package (or single chip), we also need higher frequency harmonic testing capabilities. In order to create smaller mobile phones, front-end modules are more common. Figure 5 shows a typical front-end module. As shown in Figure 5, the front-end module includes a power amplifier, a switch, and a filter. In a typical GSM/EDGE mobile phone, since the switch must work at high power (up to 36dBm), the harmonic components of these devices must be tested. This requires testing the 6th-order harmonic components (while the fundamental frequency is 1.9GHz), requiring a test capability of 11.4GHz, which greatly exceeds the test capability of the ATE test system commonly equipped today, thus driving the development of a new wireless test technology. summary There are nearly 2 billion wireless product users in the world today. We have described above the many challenges faced in testing these wireless devices, including challenges in RF technology as well as challenges in high-speed digital testing. These changes are very common and make testing more complex. Credence recognizes these challenges and has been working hard to find solutions to them. With the help of the ASL 3000RF and Sapphire test systems, we can definitely meet these challenges. With Credence as a partner, you not only have advanced technology, but also effective and low-cost test solutions. Both are indispensable for success. | 
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