This section provides overview, applications, and principles of surface acoustic wave (saw) filters. Also, please take a look at the list of 13 surface acoustic wave (saw) filter manufacturers and their company rankings.
A SAW filter is a filter that can selectively extract electrical signals with specific frequencies.
By using surface waves propagating through a piezoelectric element to filter mechanical vibrations, specific frequency components can be passed through or blocked.
A surface wave is a wave that travels over the surface of a medium, and its amplitude rapidly decreases from the surface to the interior.
In a SAW filter, when an electrical signal is an input, it is converted into mechanical vibration by a piezoelectric element, only specific frequencies are selected, and the signal is output again as an electrical signal.
SAW filters are often used in wireless communication devices such as cellular phones, TV tuners, and wireless LANs because of their low loss and excellent cutoff characteristics.
SAW filters are particularly used to reduce noise and improve the sound quality of cell phone calls, etc. Because of their low cost and the ease with which they can be made smaller and thinner, they are indispensable to the increased functionality of cell phones. In addition, the number of bands per handset is increasing year by year as the frequencies used in handsets rise.
The SAW filters has a structure in which electrodes are arranged in a comb shape on a piezoelectric substrate. When voltage is generated by the input electrical signal, vibration is generated in accordance with the distance between the electrodes arranged in a comb shape. This vibration is amplified by resonance caused by the multiple comb-shaped electrodes. The vibrations at this time become surface waves that eventually propagate to the electrodes for detection. There, the filter is achieved by converting the mechanical vibration back into an electrical signal.
The characteristics of the filter, such as how much frequency is transmitted, are determined by the properties of the piezoelectric material and the electrode structure. Since the speed of propagation of the surface varies from material to material, the performance of the filter depends greatly on the type of piezoelectric material used. Commonly used materials are quartz crystals and single crystals of lithium compounds, etc. The thinner the material, the more applicable it is to high frequencies. Therefore, coupled with the goal of cost reduction, glass substrates coated with these piezoelectric materials are increasingly being used.
SAW filters are filter elements that utilize surface acoustic waves on a piezoelectric substrate, while BAW filters have a different principle.
BAW filters have structures known as FBAR-type (Film Bulk Acoustic Resonator) and SMR (Solid Mounted Resonator) types. Specifically, the FBAR has a cavity below the resonator to allow the piezoelectric film to vibrate freely, while the SMR has a multilayer acoustic film below the resonator to reflect the acoustic waves.
SAW filters are often used in the 600 MHz to 2 GHz frequency band because of their cost advantages. BAW filters, on the other hand, tend to be more complex and costly, but they have the advantages of high Q and steep filter characteristics and are mainly used in the US band in the 1800 MHz band and in the higher frequency range above 2 GHz.
SAW filters are also available as TC-SAW filters with temperature characteristic control compensation, which are used in the market for frequency management by temperature control as well as low cost.
The number of SAW filters, which are indispensable for Tx (transmit) and Rx (receive) frequency assignment in FDD modulation for 3G (WCDMA) and 4G (LTE) modulation, has been increasing in recent years.
The market for SAW filters continues to grow, especially for high-end models, because the terminals need to be globally usable; therefore, modularization and miniaturization are remarkable, and multiple filters are installed in a single communication module, which in turn is installed in multiple communication modules for each frequency category. The market for SAW filters continues to expand.
The number of manufacturers of SAW filters are large, and Japanese electronic component manufacturers are increasing their presence in the market.
In the 5G market, the 3-6 GHz band, such as UHB (UltraHighBand) and Sub6 GHz, is mostly supported, and BAW filters have a large presence in this market. In particular, US manufacturers (Broadcom and Qorvo) are gaining market share for BAW filters.
*Including some distributors, etc.
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