Current status and challenges of SAW filters and introduction of new IHP SAW filters

I’ve been swearing before, I’m sorry, I’m sorry. IHP SAW is also known as Incredible High Performance SAW, or simply called Super SAW. When I first saw this name, I was truly shocked and couldn’t help but admire its boldness. Let’s take a look at Murata’s promotional materials here. The radio communication terminal includes an RF filter operating in the frequency range of 800 to 2500 MHz. The most commonly used RF filter today is the Surface Acoustic Wave (SAW) filter. It uses piezoelectric crystals like quartz, lithium niobate, or lead titanate, which are polished and then coated with a thin metal film. Through photolithography, two sets of interdigital electrodes are created—called the input and output interdigital transducers. When an AC voltage is applied to the input electrode, the piezoelectric crystal vibrates, generating surface acoustic waves at the same frequency as the signal. These waves propagate along the surface of the substrate and in the direction of the interdigital electrodes, hence the term "surface acoustic wave." One direction of the wave is absorbed by a sound-absorbing material, while the other is transmitted to the output electrode, where it is converted back into an electrical signal. In recent years, we've also seen more applications of Bulk Acoustic Wave (BAW) filters. Unlike SAW filters, BAW filters use vertical propagation of sound waves. For BAW resonators using quartz as the base, metal layers on both the top and bottom of the quartz excite the sound waves, causing them to bounce between the surfaces and form standing acoustic waves. The thickness of the slab and the mass of the electrodes determine the resonant frequency. BAW filters have high Q values and can achieve narrower transition bands than traditional SAW filters, making them suitable for higher frequency bands. Murata has now introduced a new SAW filter called IHP SAW, which overcomes some of the limitations of conventional SAW filters and even outperforms BAW filters in certain aspects. This article will explore the features and advantages of this innovative technology. 1. Current Status and Challenges of SAW Filters RF filters play a crucial role in the transmit and receive links of RF terminals, allowing specific frequencies or frequency bands to pass while blocking unwanted signals. They typically consist of multiple resonant units connected in different circuit configurations, such as a ladder circuit. The design of these circuits determines the filter's bandwidth and performance. An important characteristic of RF filters is the steepness of the transition band—the curve between the passband and stopband. A narrow transition band increases the difficulty of filter design. To improve the steepness, both the circuit configuration and the quality factor (Q value) of the resonant unit are essential. Traditional SAW filters based on single-crystal LiTaO3 substrates are widely used, but they face challenges in high-frequency bands. Another emerging RF filter is the BAW filter, which uses vertical sound wave propagation. Although more complex to manufacture, BAW filters offer higher Q values and better performance in difficult frequency ranges. However, they often suffer from poor temperature stability. In this context, Murata has developed the IHP SAW, a new generation of SAW filters that overcome some of the weaknesses of traditional designs. This technology not only matches the performance of BAW filters but also offers superior temperature characteristics. 2. Characteristics of IHP SAW IHP SAW filters are designed with three key features: (1) high Q value, (2) low frequency temperature coefficient (TCF), and (3) excellent heat dissipation. (1) High Q Value IHP SAW filters achieve significantly higher Q values compared to conventional SAW filters. By focusing the energy of the surface acoustic wave on the substrate, the filter minimizes losses during wave propagation. In the 1.9 GHz band, the peak Q value reaches over 3000, compared to around 1000 for traditional SAW filters. Figure 3 shows an example of an IHP SAW filter operating in Band25, a traditionally challenging frequency range. The measured insertion loss is 1.5 dB in the Tx band and 2.1 dB in the Rx band, with isolation levels of 57 dB and 59 dB respectively. These results meet the demanding requirements of modern communication systems. (2) Low Frequency Temperature Coefficient (TCF) IHP SAW filters significantly reduce the TCF, achieving stable performance across a wide temperature range. While traditional SAW filters have a TCF of about 40 ppm/°C, IHP SAW filters show TCF values as low as ±8 ppm/°C. With optimized substrate design, this can be further reduced to near-zero. (3) Good Heat Dissipation IHP SAW filters efficiently dissipate heat generated by the IDT, reducing temperature rise by nearly half compared to conventional SAW filters. This improved thermal management ensures greater reliability and stability, especially under high-power conditions. 3. Future Prospects IHP SAW filters operate effectively across a wide frequency range, from 800 MHz to 2.5 GHz. Recent tests have shown promising performance at 3.5 GHz, a frequency range traditionally considered difficult for SAW filters. As mobile devices evolve toward high-speed communication, the demand for compact, high-performance RF components continues to grow. IHP SAW filters offer a compelling solution for next-generation communication systems. Additionally, their flexibility in bandwidth adjustment and miniaturization potential make them ideal for modern, space-constrained devices. With its advanced performance and versatile design, the IHP SAW filter represents a significant leap forward in RF filter technology.

Solar Charge Controller

Photovoltaic charge controller,Solar Charging Controller,MPPT Solar Charger

Ningbo Taiye Technology Co., Ltd. , https://www.tysolarpower.com