RF front-end module, this article is enough.

Name: Liu Xuan? Student number:19020100412 College: School of Electronic Engineering.

From: /p/297965743

Introduction of RF front-end module technology embedded in cattle reading guide

Embedded bovine nose RF front end? Filter?

How can China enterprises overcome "takenism" and develop rapidly and iteratively?

Mosaic ox script

RFFE(Radio Frequency Front-End) chip is the core component to realize the communication function of mobile phones and various mobile terminals, and the global market exceeds10 billion US dollars. The overall rise of local mobile phones in 10 laid a solid industrial foundation for the development of local RF front-end industry; The changes in the commercial and global trade environment of 5G in China have added two bundles of firewood to the local RF industry. The RF front-end chip industry has a development history of 15 years in China, and its innovation and entrepreneurship activities are very active. There are dozens of enterprises of various types, which is also an area of great concern to the market and capital. The author of this paper is fortunate to have worked in the RF chip industry for 1 1 year, and achieved today's 5G from the 2G era. He has also worked in foreign companies, private enterprises and state-owned enterprises, and directly developed and mass-produced every kind of RF products. This paper summarizes the discussion between the author and some friends in the industry in recent years, trying to sort out the technical market and business logic of RF module products. At the same time, local radio frequency has developed for more than ten years, competition is the main line of the industry, and cooperation and friendship are very scarce resources. This paper will focus on sharing the knowledge about modularization, hoping that more local manufacturers can share the great opportunities of modularization through cooperation.

introduce

According to the keynote speech delivered by Professor Wei Shaojun at the "2020 Global CEO Summit" entitled "The Right Way in the World is Vicissitudes-On the Strategic Strength under Great Changes", statistics show that American companies have the highest dependence on the China market (in terms of revenue ratio), as shown in the following figure. We can see SKYWORKS, Qualcomm, Qorvo and Broadcom, four American RF giants (SKYWORKS and Qorvo are mainly engaged in RF business; Qualcomm and Broadcom (including radio frequency services) have just occupied the top four in the rankings.

International situation of RF front-end

RF front-end technology mainly focuses on filter PA, power amplifier (PA), low noise amplifier and RF switch. At present, the global RF market is dominated by four American RF companies, Skyworks, Qualcomm, Qorvo, Broadcom and Murata.

The five RF giants have more than 90% market share in PA and LNA. As for filters, they are divided into two main surface acoustic wave technologies, surface acoustic wave (SAW) BAW and bulk acoustic wave (BAW). At present, Murata accounts for half of the SAW filter market, Skyworks accounts for about 65,438+00%, Qorvo accounts for about 4%, and the rest is divided by big manufacturers such as Solar Inductor and TDK. 90% of BAW filter market is occupied by American enterprises.

It can be seen that the RF front-end is a huge market, which can accommodate the sustainable development of the five international giants. International giants have a large technological span and strong modularity; Modular products are the main track of international competition. Every giant has BAW technology or its substitute.

Present situation of RF front-end in China

There are many articles about the domestic situation of RF front-end, so I won't go into details here, only a few conclusions are given:

1. Local companies generally take discrete devices as the main direction; Discrete devices are the main track of local competition at present. 2. Local companies lack advanced filtration technology and products, and modularity is generally not strong.

Challenges and opportunities of 5G modularity

The challenge of PCB wiring space and RF debugging time has sunk to entry-level mobile phones, which has opened the way for iterative upgrade of domestic module chips.

RF module chip is not a new product line. In fact, the use of RF module chips almost coincides with the commercialization of LTE. /kloc-in the past 0/0 years, various complex RF modules have been widely used in flagship mobile phones of various brands; At the same time, in a large number of entry-level mobile phones, the scheme of discrete devices can completely meet all requirements. So in the past 10 years, there have been two completely different markets: the modular scheme of flagship models; Discrete scheme of entry-level model. The module scheme requires "high integration and high performance", so the price is also very high; The separation scheme requires "medium and low integration, medium performance" and the price is relatively low. There are huge technical and market differences between the two schemes, which we can call the "module gap" in the 4G era.

"Module Gap" in the 4G Era

The arrival of 5G has completely changed this situation.

Compared with 2~4 antennas of 4G entry-level mobile phones, the number of antennas of 5G entry-level mobile phones has increased to 8~ 12; The frequency bands and frequency band combinations that need to be supported are also greatly increased on the basis of 4G. As we all know, the number of RF components has a strong correlation with the number of antennas and frequency bands, which means that the number of RF components has increased dramatically. At the same time, due to the requirements of structural design, the PCB area left for the RF front end of the 5G mobile phone cannot be increased, so the area of the discrete scheme greatly exceeds the available PCB area. This is the bondage brought by space.

Another challenge comes from debugging time. The debugging time of 4G RF using discrete device scheme is generally less than one week. With the significant increase in the complexity of 5G radio frequency, assuming that a separate scheme is used, it may bring about a 3-5 times increase in debugging time; In terms of cost, it also needs to consume more expensive 5G test equipment and engineer resources familiar with 5G testing. If modules are used, most debugging has been realized internally in the process of module design, and more debugging workload will be moved to the software side, so debugging efficiency will be greatly improved. This is the constraint brought by time.

The limitation of time and space is powerful and universal. Therefore, in the entry-level 5G mobile phone, there is a natural demand for the "medium and low performance and high integration" module, which forms a pin integration with the "medium and high performance and high integration" module of the flagship mobile phone. Because we all need highly integrated modules, but the index requirements are different, domestic module chips can evolve from "medium and low performance" (5G entry-level mobile phone) to "medium and high performance" (5G flagship mobile phone) iteratively. Therefore, the "module blank" is filled.

Everything has two sides. After the "module gap" has been bridged, there are risks in the space of the separate market; For local enterprises focusing on discrete chips, they also need huge resources and strength to find their own position in module products; If we can't break through, we will enter the bottleneck stage in the near future.

In the early stage of 5G, there was also a hybrid scheme in the market, that is, a scheme of mixing discrete devices and modules. There are many objective reasons for the emergence of this scheme, including the "module gap" formed in history. This plan is the product of compromise, sacrificing some key indicators and making concessions on area. If there is no chip company focusing on domestic modules, there will be no excellent domestic module chips; If there is no excellent domestic module chip, the price of the module scheme will always be high.

Brief classification of filtering technology

BAW filter: namely bulk acoustic wave filter. It has the advantages of small insertion loss and large out-of-band attenuation, and is insensitive to temperature changes. The size of BAW filter will shrink with the increase of frequency, so it is especially suitable for medium and high frequency communication above 1.7GHz, and has obvious advantages in the application of 5G and sub-6G.

SAW filter: namely surface acoustic wave filter. Piezoelectric materials such as quartz crystal, lithium niobate and piezoelectric ceramics are special filter devices by using their piezoelectric effect and physical characteristics of surface wave propagation. SAW filter has the advantages of stable performance, convenient use and wide frequency band, and is the mainstream application of frequencies below 1.6GHz. However, it has some disadvantages, such as large insertion loss and serious heating problem, and is not suitable for processing high frequency signals above 1.6GHz.

LC-type filter: namely inductance-capacitance filter. LC filter is generally composed of filter capacitor, reactance and resistance, and inductance and capacitance together form LC filter circuit.

Brief classification of RF modules

The RF front-end module integrates two or more discrete devices, such as RF switch, low noise amplifier, filter, duplexer and power amplifier, into one module, thus improving integration and performance and realizing miniaturization. According to different integration methods, the RF link of the main antenna can be divided into: FEMiD (integrated RF switch, filter and duplexer), PAMiD (integrated multimode and multiband PA and FEMiD), LPAMID (integrated multimode and multiband PA and FEMiD) and other diversity antennas, and can be divided into DiFEM (integrated RF switch and filter) and LFEM (integrated RF switch, low noise amplifier and filter).

Main antenna RF link

Diversity antenna RF link

"Value Density" of RF Front End

Because the PCB area of 5G mobile phone is a limited resource, we need to "squeeze in" more RF functional devices in 5G mobile phone. Therefore, when evaluating each type of RF devices, we need to establish a parameter to describe it uniformly as a comprehensive index reflecting its value and PCB occupied area.

ValueDensity= (average selling price ASP)/ (chip package size)

Next, we use VD value as a tool to analyze the situation of filter, power amplifier and RF module respectively.

1. VD value of filter.

First of all, because the filter usually needs an external matching circuit, the actual VD value is lower than that of the device. Let's ignore this factor first. According to the above data, we can draw some conclusions: from LTCC to tetraploid, VD value keeps increasing, from 1.2 to 10.0, and the increase is relatively fast.

2. VD value of power amplifier

According to the above data, we can also see: a) From 2G to 4G, VD value increased from 0.6 to 1.5. B) The VD value of miniaturized products that evolved from 4G to CAT 1 and high-power PA that evolved to HPUE or Phase5N increased to about 2.

3. VD value of RF module

According to the above data, it can be observed that: a) the VD value of the receiving module is about 5; B) The H/M/L LFEM and VD values of small packages in the receiving module are very prominent, which are greater than10; C) transmitting module (except FEMiD), with VD value between 4 and 6; D) FEMiD has the highest VD value of the transmitting module. Therefore, when FEMiD is mixed with MMMB PA with low VD value, reasonable PCB layout efficiency can be realized.

At the same time, we also added the reference data of technology localization rate and market localization rate. Generally speaking, if the market localization rate is low, or the technology localization rate far exceeds the localization rate figure, the VD value will be artificially high. After the market share of local corresponding products increases, there will be obvious room for price reduction in the future.

Radio frequency transmitting module of five mountains

Transmit1:The integration of PA and LC filters is mainly used in the new 5G frequency band from 3 GHz to 6 GHz. Typical products are PAMiF or LPMIF of n77 and n79. The 5GPA design of these new frequency bands is very challenging, but because the spectrum of the new frequency band is relatively clean, the requirements for filters are not high, and LC filters (IPD, LTCC) are competent. On the whole, this kind of product is challenging but not complicated, and its technology and cost are absolutely controlled by PA.

Emission 2: the integration of PA and BAW (or high-performance SAW). The typical products are PAMiF of n4 1 or iFEM of Wi-Fi, and the frequency band is about 2.4GHz. The frequency band of such products is common, and the technical specifications of PA are challenging but not high. Because it works near 2.4GHz and the frequency band is very crowded, it is necessary to integrate high-performance BAW filters into typical products to realize * * * storage. Because the filter function of this kind of products is not complicated, PA still has technical control; But in terms of cost, the filter may exceed PA. Generally speaking, this kind of products are challenging but not complicated, and PA has certain control.

Launch 3: low-band launch module. LB (L)PAMiD usually integrates 4G/5G frequency bands (such as B5, B8, B26, B20, B28, etc.). ) 1GHz, including high-performance power amplifier and several low-frequency diplexers. In different schemes, we can also integrate GSM850/900 and 2GPA of DCS/PC to further improve the integration level. Low-frequency diplexers usually need TC-SAW technology to achieve the best system index. According to the needs of the system scheme, if a low noise amplifier (LNA) is integrated on the basis of LB PAMiD, this kind of product is called LB LPAMiD. It can be seen that the complexity of this kind of products is already relatively high: in terms of PA, it is necessary to integrate high-performance 4G/5GPA, and sometimes it is necessary to integrate high-power 2GPA cores; ; For filters, there are usually 3~5 TC-SAW diplexers in wafer level package (WLP). From the original assembly (assuming that 2GPA needs to be integrated), the proportion of PA/LNA part and filter part is basically the same. LB (L)PAMiD requires a relatively balanced technical capability, so the third step appears at the junction of PA and filter.

Launch 4: Femid. Such products usually include various filters/diplexers/multiplexers from low frequency to high frequency, and antenna switches in the main path; Do not integrate PA. FEMiD products usually need to integrate LTCC, SAW, TC-SAW, BAW (or I.H.PSAW with equivalent performance) and SOI switches. Murata's definition of such products is that in the past eight years, it has occupied the absolute dominance of this market. Mobile phone manufacturers such as Samsung and Huawei have used or are using such products in a large number of high-end mobile phones. As mentioned above, the competitive PAMiD suppliers are mainly concentrated in North America; Considering the diversification of supply chain, some mobile phone models with very large shipments can consider using MMMB (Multi-mode Multi-frequency) PA plus FEMiD architecture. The qualified suppliers of MMMB PA are widely distributed in North America, China and South Korea, while Murata's FEMiD production capacity is very huge (mainly in LTCC and SAW). As mentioned above, the VD value of FEMiD is very high, and the space utilization rate of the overall scheme is also within a reasonable range.

Launch 5: m/h (l) PAM ID. This kind of product is the most valuable and difficult to synthesize in the RF front-end market, and it is the peak of the RF front-end market segment. M/H usually covers the frequency range of1.5 GHz to 3.0 GHz, which is the golden frequency band of mobile communication. The first four FDDLTE frequency bands Band 1/2/3/4 are in this range, and the first four TDD LTE frequency bands B34/39/40/4 1 are in this range, and all commercial frequency bands of TDS-CDMA are in this range. The earliest commercial carrier aggregation scheme also appeared in this range (realized by B 1+B3 quadrupler), and important non-cellular communications such as GPS, Wi-Fi 2.4G and Bluetooth also worked in this range. It is conceivable that the biggest characteristics of this frequency band are "crowding" and "interference", which is also a broad stage for high-performance BAW filters to play their skills. Due to the long commercial time in this frequency band, PA technology in this frequency band is relatively mature, and the core challenge comes from filter devices.

First of all, explain why this frequency is the golden frequency of mobile communication. In the long development process, the driving force of mobile communication comes from the popularization of mobile terminals, and the core challenge of the popularization of mobile terminals lies in the performance and cost of terminals. If the frequency is too high, such as above 3GHz and above 10GHz, the characteristics of semiconductor transistors will rapidly decline, making it difficult to achieve high performance. But for too low frequencies, such as below 800MHz and below 300MHz, the size of the antenna will be very large, and the inductance and capacitance used for RF matching will also be very large. Under the limitation of terminal size, the ultra-low frequency band RF performance is difficult to reach the system index. In short, from the performance point of view of active devices (transistors), we hope that the frequency is lower; Judging from the performance of passive devices (capacitors, inductors, antennas), the frequency is expected to be higher. The essential conflict between active devices and passive devices, the compromise of application end and the integration in the module, like two powerful cold currents and warm currents, converge in the most magnificent main channel of human mobile communication 1.5~3GHz frequency band, forming the most complex and valuable gold fishing ground for terminal RF: M/HB (L)PAMiD. Well done!

At present, the market of such high-end products is mainly occupied by American manufacturers such as Broadcom, Qorvo and RF360. The picture below shows the chip opening analysis provided by Qorvo Company in its official WeChat account. It can be seen that this kind of products include BAW with 10 or more, 2~3 GaAs HBT, 3~5 SOI and 1 CMOS controller, which is the most technically complex among RF products. This kind of products usually need to integrate ultra-high VD devices such as quadrupler or quintupler.

M/H LPAMiD open cover diagram

Radio frequency receiving module of five mountains

The five mountains model of the receiving module is shown in the above figure.

Receiving 1: RF switch and LNA are implemented on a single chip using RF-SOI technology. Although it is only a single die, it is also a RF module chip with composite functions. The main technology of this kind of products is RF-SOI, which has some applications in both 4G and 5G.

Receive 2: Realize the functions of LNA and switch by RF-SOI technology, and then package and integrate with an LC-type (IPD or LTCC) filter chip. The LC filter is suitable for the requirements of large bandwidth and low rejection from 3~6GHz to 6 GHz, and is suitable for n77/n79 frequency band of 5G NR. This kind of products are mainly based on SOI technology, mainly used in 5G.

Receiving 3: Going up from receiving 3, the receiving module needs to integrate several SAW filters at first, and the integration level is getting higher and higher. Usually, it is necessary to integrate single-pole multi-throw (SPnT) or double-pole multi-throw (DPnT) SOI switches and several SAW filter channels supporting carrier aggregation (CA). In the way of packaging, there are many possible paths because there is no limit to the integration of "receiving 3". Among them, the products of international manufacturers are mainly WLP technology, which can be reused in other products with higher integration besides its advantages in reliability and product thickness.

Receiver 4: This product is called MIMO M/H LFEM. MIMO technology is mainly used in M/H frequency band (for example, B 1/3/39/40/4 1/7) to improve the communication rate, which is a mandatory requirement for some medium and high-end mobile phones to access the network. It seems that the communication industry really loves the golden frequency band M/H. Technically, these products are LNA plus switches based on RF-SOI technology, and then integrated with 4~6 M/H high-performance SAW filters. International manufacturers have begun to widely use TC-SAW technology in these frequency bands to achieve the best overall performance.

Receiving 5: The LFEM with the highest complexity of the receiving chip is H/M/L M/L. This kind of products can realize the SAW filter, RF-Switch and signal enhancement (LNA) in the frequency band of 10~ 15 with extremely high value density (about 10), which can help customers greatly. This kind of products need the highest comprehensive skills, and basically need to adopt the advanced packaging method in WLP form to meet the requirements of size, reliability and yield.

abstract

1. The core requirements of RF modules are miniaturization of various components and integration of modules.

2. Whether it is the transmitting module or the receiving module, the pure 5G module is difficult but not complicated. The most challenging and valuable module is the high complexity module supported by both 4G and 5G.