![]() ![]() ![]() One thing they have in common is that they both obsolete the need for study of classic lumped-element analog-filter design theory and practice.įigure 3: Basic SAW Filter (SAW, BAW, and the future of wireless Figure 1)įigure 4: SAW, BAW, and the future of wireless, Figure 2 SAW devices are viable up to about 1 GHz, while BAW devices conveniently overlap in coverage, starting below 1 GHz and going into the multi-GHz regime. Instead, they exploit the well-known, versatile piezoelectric effect, transforming electrical energy into acoustic waves which travel along the surface (SAW) or within (BAW) an engineered ceramic-crystal material (Reference 1). ![]() SAW and BAW technologies have matured over the past decades to create low-cost, high-performance devices with no relationship to discrete-component analog filters. Obviously, these products are very practical, and it’s largely due to using a radically different approach to analog filters: the surface acoustic wave (SAW) and the bulk acoustic wave (BAW) filters (and their film bulk acoustic resonator – FBAR – sibling). If there was no alternative to discrete-component filters, many of the devices with which we are surrounded would be impractical due to size, performance, consistency, and cost. ![]() Parasitics along with component tolerance and drift make them a real challenge, and these filters often need to be individually trimmed to counter their difficult-to-model realities. However, these lumped-element filters are increasingly difficult to design and then fabricate successfully for these higher frequencies. These are valuable additions to the filter roster as they are compatible with IC processes and can eliminate need for discrete-component filters in many cases.)Ĭlassic analog filters can be used into the hundreds of MHz and even GHz ranges. There are also quasi-analog switched-capacitor filters which use charge-balancing and clocked switching among multiple capacitors to implement filter functions. (Of course, those are just your classic all-analog filters. 【On Demand/Watch Now】One Chip Solution to Reduce Time-to-Market with MOTIX™ Motor System IC Then there are their attributes: first order, second order, roll-off, passband ripple, stopband ripple, phase performance, balanced (differential) – that’s another long list. Still, classic filter theory is a subject which can drive students and engineers to weird states of mind, as they come in mind-boggling and mind-numbing versions and realizations There are so many distinct topologies, such as pi-filter (Figure 1), Chebyshev, Sallen-Key, Butterworth, Cauer (elliptical), and Gaussian, to cite a few. Whether low-pass, high-pass, bandpass, or notch, they are necessary even if they don’t appear to add value to the signal as they improve SNR, minimize interference from nearby channels, and attenuate 50/60 Hz pickup, to cite just a few of their many uses. This makes sense because filters play multiple essential roles in the signal path, regardless of application area. Whether as passive or active designs, it sometimes seems that they have been studied “to infinity and beyond” via theoretical constructs with very intense math, with practical “application note” designs and BOMs, and even with hands-on circuits with actual physical-construction details. Analog, discrete-element filters have served us well for over a hundred years, but maybe we now need to focus education on filters for the GHz world, such as SAW and BAW devices?Īnalog filters using inductors, capacitors, and resistors are critical to most circuits and systems. ![]()
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