BAW filters help 5G achieve high-quality communications and higher efficiency
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Technological innovation derived from 5G
1) Millimeter wave communication
The method of using millimeter waves for communication is called millimeter wave communication. The wavelength of millimeter waves ranges from 1 mm to 10 mm, and the frequency ranges from 30 GHz to 300 GHz.
λ= V/f (V=C speed of light, f the higher the frequency, the shorter λ)
The higher the frequency (the shorter the wavelength), the closer it is to straight line propagation (the worse the winding ability), and the more serious the attenuation. The wavelength of millimeter waves ranges from 10 mm to 1 mm, and the frequency ranges from 30 GHz to 300 GHz. Therefore, the use of high frequency bands by 5G will greatly weaken its coverage.
Advantages of millimeter waves: ultra-wideband, narrow beam, less interference, high transmission quality, and small component size.
2) Small base station technology
Due to the serious attenuation of high-frequency electromagnetic waves, which is particularly obvious when there are obstructions, the propagation distance is shorter. For the stability and continuity of the signal, the demand for base stations will be much greater than 4G. Compared with macro base stations, a macro base station can cover a large area. Small base stations are small in size and large in number. They can be installed anywhere and arranged flexibly. In the future, they may even be hidden in every corner of the street, fully integrated into people's lives, and meet the needs of various scenarios.
Advantages of small base stations: low power consumption, compact appearance, complete base station (the entire system includes BBU + RRU + optional routing equipment), cellular mobile communication technology that can work in both licensed and unlicensed spectrum, and indoor and outdoor deployment.
3) Massive MIMO and beamforming technology
MIMO (Multiple Input Multiple Output) is a technology that allows multiple inputs and multiple outputs. By arranging antenna arrays, each pair of antennas can transmit information independently to achieve information transmission between base stations and communication equipment. Multiple transmitting antennas and receiving antennas are used at the transmitting and receiving ends respectively to increase channel capacity without occupying additional spectrum resources and achieve effective utilization. Traditional MIMO systems only support 8 antenna ports. In Massive MIMO systems, the number of antennas configured at base stations will increase several times. Currently, (32/64/256) array antennas are used in a large number of application designs to modulate their own beams for the target receivers, isolate signals and do not interfere with each other, give full play to the spatial freedom of the system, and greatly improve the efficiency of spectrum utilization.
Beamforming is a combination of antenna technology and digital signal processing technology, and is used for directional signal transmission or reception. It refers to the ability to automatically adjust the radiation pattern of the antenna array according to specific scenarios. Beamforming technology is an application form of MIMO, which enables users in a frequency band to transmit data simultaneously without interfering with each other, so as to achieve signal superposition at the receiving end and thus improve the strength of the received signal. This technology allows energy to be focused on the user without scattering in other directions, thus establishing a reliable connection.
4) New multi-carrier technology
Carrier refers to a radio wave of a specific frequency that carries data. Multi-carrier means using multiple carrier signals (dividing the channel into several orthogonal sub-channels) to convert the data signal to be transmitted into parallel low-speed sub-data streams, and then modulate them to transmit on each sub-channel. The use of multi-carrier technology is mainly to cooperate with large-scale MIMO technology, which has the characteristics of high spectrum efficiency, strong flexibility and low complexity.
Carrier aggregation technology aggregates multiple carriers into a wider spectrum, and at the same time aggregates discontinuous spectrum fragments together to obtain a larger bandwidth, greatly improve the transmission speed, and reduce latency. Its application in 4G can aggregate 2-5 LTE component carriers (small bandwidth, usually 20M) together to achieve a maximum transmission bandwidth of 100MHz.
With the rapid development of mobile Internet and Internet of Things, after the realization of 5G network, the most intuitive feeling is that the network speed has been qualitatively improved, from the fastest 12.5MB/s of 4G to 20Gbps. Such speed will completely change our lives, from 2G traditional communications to QQ in the 3G era, and now to WeChat, Douyin and other short video software. The upcoming 5G will have unlimited possibilities, including virtual reality, ultra-high-definition video, image projection, and telemedicine. After all, the future is here.
The value of RF front-end devices will continue to rise in the 5G era
The RF front end includes RF power amplifiers, RF low noise amplifiers, RF switches, RF filters, duplexers, isolators and other devices.
The main driving force for 5G technology upgrades comes from the demand for low power consumption, high performance and low cost of related products.
1) Network communication upgrades place increasing demands on RF front-end performance
RF front-end is a basic component of the system and a core component of mobile smart devices. Regardless of the communication protocol or frequency, the RF front-end is indispensable.
From 2G GSM, 3G WCDMA, to 4G LTE-Advanced, each generation of mobile networks brings new communication protocols, and the complexity increases exponentially, placing higher and stricter requirements on the RF system in mobile phones. The 5G era will bring a new network architecture. In addition, Massive MIMO technology, carrier aggregation technology, etc., have put forward higher requirements on the performance of RF devices in devices.
Bandwidth: the network speed that consumers refer to, that is, the total amount of bit information transmitted per unit time. The download speed is determined by the bandwidth. In 2018, the average download speed of China Mobile's 4G LTE was 30Mbps, and the maximum user bandwidth of 5G will reach 1Gbps (1024Mbps). The peak speed will reach 20Gbps. Comparing the history vertically, in terms of design speed, 2G is 20 times faster than 1G, 3G is 20 times faster than 2G, and 4G is 10 times faster than 3G. The 100-fold bandwidth of 5G relative to 4G will be the biggest improvement in history; such a speed is 40 times the speed required for 4K high-definition live streaming (25Mbps). The 100-fold bandwidth of 5G relative to 4G will be the biggest improvement in history. This is inseparable from the high bandwidth of the 5G system. The high bandwidth of the 5G system places particularly strict requirements on the power amplifier.
Delay: 5G's improvement in connection quality is far more than just reflected in bandwidth. The delay of the 5G network is the highlight. Network communication can never get around the delay. As an indicator of the time from when data is sent to when it is received, the importance of delay is no less than that of bandwidth. If bandwidth determines the download speed of the network, then delay determines the response speed of the network.
From the data, the average delay of the most advanced 4G LTE is about 90 milliseconds, and the average delay of ordinary wired networks is about 50-120 milliseconds. The target delay of 5G is within 10 milliseconds, which is about 1/50 of 4G and far lower than the current ordinary wired networks. We have reason to believe that the ultra-low delay of 5G will be a nuclear bomb that detonates the potential of the Internet!
2) Network communication upgrades require more and more RF front-ends
Let's take smartphones as an example. In its RF front-end system, the RF front-end includes SAW/BAW filters, duplexers, power amplifiers, switches and other devices. From 1G, 2G, 3G, 4G to 5G, there are more and more operating frequency bands, and at the same time, communication standards are required to be backward compatible to meet multi-mode and multi-frequency requirements. Different frequency bands have more and more demands on PA, LNA, filters, antenna switches, duplexers, etc.
Rising mobile phone sales and increased frequency bands drive growth in RF front-end numbers
According to relevant statistics, the global RF front-end market size grew at an annual rate of about 12% from 2010 to 2016, reaching US$11.488 billion in 2016, and will continue to grow at a high rate of more than 12% in the future. It will be close to US$19 billion in 2020. In the past few years, the communication industry has upgraded from 2G (GSM/CDMA/Edge) -> 3G (TD-SCDMA/CDMA2000/WCDMA), -> 4G (TD-LTE/FDD-LTE). The two major network communication upgrades have put higher and higher requirements on the RF front-end, and the quantity and price of the RF front-end have increased. With the approach of 5G commercialization, the existing mobile communication and IoT communication standards under the 5G standard will be unified, so the application field of RF front-end chips will be further expanded.
BAW/SAW filters have great potential
5G operates at high frequencies, and has higher requirements for high-frequency performance of RF front-end devices. Compared with 4G, it uses higher frequencies. Compared with medium and low frequency circuits, high-frequency circuits need to be reconsidered and designed from materials to devices, from baseband chips to the entire RF circuit. High-frequency circuits basically need to be customized for high-frequency signals and product structures, and are characterized by miniaturization. In addition, high-frequency circuits require detailed consideration of device size and circuit layout.
Filters are devices used to eliminate interference and filter clutter. Smartphones, satellite navigation, small base stations and other RF front-end systems all require filters to work properly, filtering out-of-band interference and noise to meet the signal-to-noise ratio requirements of RF systems and communication protocols. In the future, in smartphone terminals, SAW/BAW filters will account for more than half of the value of mobile phone RF front-ends and are important components of RF front-ends.
SAW surface acoustic wave filter
SAW propagates on the surface of piezoelectric substrate material. The basic structure is to make two interdigital transducers on the polished surface of piezoelectric material. They serve as the transmitting transducer and the receiving transducer respectively. When voltage is applied to the piezoelectric substrate (changing the atomic structure inside the crystal), the crystal will undergo mechanical deformation, and the transmitting transducer will convert electrical energy into mechanical energy. When this crystal is mechanically compressed or stretched, the receiving transducer converts the acoustic signal into an electrical signal for output. The filtering process is realized in the conversion from electricity to sound and from sound to electricity. The SAW filter can be equivalent to a two-port passive network.
BAW Bulk Surface Wave Filter
BAW propagates vertically in the piezoelectric material. The most basic structure is a piezoelectric film sandwiched between two metal electrodes. The metal embedded on the top and bottom sides of the piezoelectric film plate excites the sound waves, causing them to bounce from the top surface to the bottom to form standing sound waves. The thickness of the plate and the mass of the electrodes determine the resonant frequency. The minimum loss and maximum Q value are obtained.
At high frequencies where BAW filters are very useful, the thickness of the piezoelectric layer must be on the order of several microns, so thin film deposition and micromachining techniques must be used on the carrier substrate to realize the resonator structure.
BAW: (BAW-SMR devices) and (FBAR filters)
BAW-SMR filter, in order to prevent the sound wave from spreading to the substrate, reflects the sound wave into the piezoelectric layer. A Bragg reflector is formed by stacking thin layers of different stiffness and density. This method is called a BAW or BAW-SMR device with a firmly mounted resonator. The reflector is composed of several layers of alternating high and low impedance layers, such as the first layer has a large acoustic wave impedance, the second layer has a small acoustic wave impedance, and the third layer has a large acoustic wave impedance. The thickness of each layer is λ/4 of the sound wave, so that most of the waves will be reflected back and superimposed on the original waves. The overall effect of this structure is equivalent to contact with the air, and most of the sound waves are reflected back.
FBAR filter is the abbreviation of film builk acoustic resonator filter, which is translated as thin film cavity acoustic resonance filter. It is different from previous filters. It is made using silicon substrates, MEMS technology and thin film technology. At this stage, FBAR filters have characteristics slightly higher than ordinary SAW filters. Thin film technology is to etch from the back of the substrate to the surface to form a suspended thin film and cavity.
The high frequency and high performance of 5G have led to a large-scale explosion in the demand for BAW based on 4G LTE.
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