Foreword
In recent years, multi-function devices such as smartphones/tablets with high-performance applications have rapidly spread. This kind of device that incorporates communication functions is prominently highlighted by the diversity of streams, navigation, and cloud correspondence. In order to respond to the diversification of such functions and to realize a comfortable and fast communication method, it is a major issue to ensure communication capacity/communication frequency.
As a function common to communication terminals, we cite the correspondence of various networks here. The mobile communication standard is a 3G system UMTS (Universal Mobile Communication System) that realizes high-quality, high-speed data transmission based on the original GSM (Global System for Mobile Communications) 2G specification. In recent years, services called second-generation communication specifications such as LTE (Long Term Evolution) have also been introduced. LTE is a specification between 3G and 4G, also known as 3.9G, which is a communication technology that is expected to develop in the long run.
3G technology is only a speed of up to Mbps for uplink and downlink, but LTE has more than 50Mbps and downlink speed of 100Mbps or higher, achieving the same speed as fixed communication network. In the GSM/UMTS-compatible terminal, there are usually four GSM carriers, and UMTS is equipped with 2-4 frequency bands. If LTE is required, 1-2 additional frequency bands will be added. FIG. 1 is a speculative diagram of the average number of frequency bands mounted in a mobile device. As the amount of traffic on the network increases, communication capacity and communication frequency are guaranteed, and the number of piggybacked LTE bands is expected to increase rapidly.
Figure 1: Estimation of the average number of bands carried in mobile devices
Shown in FIG. 2 is an exemplary diagram of a front end configuration of a GSM/UMTS/LTE corresponding terminal. In order to ensure high-quality communication quality, multi-function terminals are equipped, and in addition to these communication specifications, communication functions such as Wi-FiTM, Bluetooth®, and GPS are also widely used. It maintains the versatility and multi-band of mobile devices. In order to ensure the accommodation space within the volume defined by the product itself, the miniaturization of electronic components constituting the RF portion is also growing.
Figure 2: Example of front-end configuration of a GSM/UMTS/LTE-compatible terminal
Reduced capacity in the front-end configuration section
The electronic components mounted on the front end portion of the mobile terminal are becoming smaller and smaller as the number of communication functions and the number of mounted frequency bands increase. While forming a wireless communication device, an RF transceiver IC (RFIC; radio frequency integrated circuit) is an essential component. The RFIC has the function of varying the frequency of the wave, adjusting and adjusting the signal. The trend of the input terminal of the receiving end of the RFIC is to convert the balanced input into an unbalanced input, and achieve the miniaturization of reducing the number of RFIC terminals by implementing signal processing of the unbalanced input. In addition, the signal strength of the PA is increased, and MMMB (Multimode Multi-Band) PA is used. If only a PA corresponding to one frequency band is used, it is necessary to have a PA with a number of bands, and MMMBPA corresponds to a multi-band, and one component can cover a plurality of frequency bands. If you use this, you can reduce the mounting area by reducing the number of components. The matching components such as inductors and capacitors are no exception, and the miniaturization from 0603 size (0.6 & TImes; 0.3mm) to 0402 size (0.4 & TImes; 0.2mm) can be advanced.
Figure 3: Cut-down of the front-end configuration section
The data is received and transmitted using different frequency bands, but to communicate at the same time, the duplexer is necessary in order to achieve the standard of the received and transmitted signals. The duplexer has different frequency bands, and can simultaneously filter the frequency of the transmission signal and the reception signal, and has a function of preventing the transmission circuit from flowing to the reception circuit. A SAW duplexer that combines the miniaturization and high attenuation of the duplexer has also been widely used. Its FDD method is the same as that of the duplexer, and the miniaturization of the SAW duplexer is more stringent.
Miniaturization of SAW duplexer
Figure 4 shows the changes in the size of the Murata SAW duplexer. The CSP model was successfully commercialized from the old cavity 3025 size (3.0 & TImes; 2.5 mm) to the later establishment of the resin sealing method, achieving miniaturization. Later, by improving the electrode design and processing technology, we continued to improve the miniaturization. Thus, in 2013, the 1814 size (1.8 & TImes; 1.4mm) CSP model SAW duplexer was successfully commercialized. It is 20% smaller than the current mainstream 2016 size (2.0×1.6mm), and it has become a new technology to support the increase in the number of bands to be mounted in the future.
Figure 4: Product size trend
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