What Is a SAW Filter?
A SAW (surface acoustic wave) filter is a device designed to selectively pass or block electrical signals at specific frequencies. It utilizes mechanical vibrations of surface acoustic waves on a piezoelectric element to achieve steep frequency selectivity. These waves, traveling across the surface of the medium, rapidly attenuate as they move deeper, enabling precise filtering.
Electrical signals input into a SAW filter are converted into mechanical vibrations by the piezoelectric element, which then selectively filters and outputs the desired frequency back as an electrical signal.
Uses of SAW Filters
SAW filters are commonly found in duplexers for wireless communication devices like smartphones, TV tuners, and wireless LANs. Their low loss, excellent cutoff characteristics, affordability, and compact, thin profiles make them essential for mobile device functionality. As mobile devices use an increasing number of communication frequency bands, SAW filters play a crucial role in band selection and wireless communication technology.
Principle of SAW Filters
SAW filters operate by converting high-frequency electrical signals into mechanical vibrations across a piezoelectric substrate with comb-shaped electrodes. These vibrations, resonating through the electrodes, generate surface waves that propagate back to detection electrodes, where they’re converted back into electrical signals. The filter’s performance is influenced by the piezoelectric material’s properties and the electrode structure, as the propagation speed of surface waves varies with the material used.
Other Information on SAW Filters
1. The SAW Filter Market
The SAW filter market is expanding to meet the increasing demands of smartphone transmission capabilities, with innovations in carrier aggregation and MIMO technologies. The need for filters in FDD modulation schemes, which transmit and receive simultaneously, is growing, especially for high-end models requiring global availability. Japanese manufacturers are notably prominent in the SAW filter market.
2. Difference from BAW Filters
While SAW filters utilize surface acoustic waves on piezoelectric substrates, BAW (bulk acoustic wave) filters operate differently, employing either FBAR (film bulk acoustic resonators) or SMR (solidly mounted resonators) principles. SAW filters are cost-effective for frequencies up to 2 GHz, whereas BAW filters, more complex and expensive, offer higher Q and sharper filter characteristics for higher frequency bands.
3. SAW Filters and 5G
In the 5G era, especially for the 3-6 GHz band, BAW filters become crucial due to their ability to handle steep and high Q-value filter characteristics required for coexistence with WiFi and addressing increased losses at higher frequencies. U.S. manufacturers like Broadcom and Qorvo lead in the BAW filter market.