The days of constructing bandpass filters from discrete components are pretty much over when it comes to the frequencies involved in modern wireless gear. That’s what makes the video we recently did with Alex Rabinovich from AVX interesting. Alex showed us a bandpass filter characteristic that’s super narrow, and the filter that creates also comes in a very small package. Rather than using discrete components, modern RF filters are likely to use multilayer organic high density interconnect technology as found in the AVX devices. MLO components contain high-dielectric-constant and low-loss materials to realize high Q passive printed elements, such as inductors and capacitors, in a multilayer stack. AVX MLO components are expansion-matched to most organic PCB materials, a measure that improves reliability compared to standard silicon and ceramic devices.
Alex showed us a frequency response of a bandpass filter manufactured using AVX proprietary thin-film operations. This bandpass filter is implemented using about 0805 size packages — this is about the size of some discrete surface-mount capacitors and inductors, but the whole filter fits inside. Rabinovich says there is nothing like it on the market right now. It is relatively new, having been introduced about a year ago. The filters exhibit low insertion loss, steep roll-offs, and a high rejection of out-of-band frequencies. They support many frequency bands and multiple wireless standards and are less than 1.0 mm thick.
Typical applications vary from test instrumentation, military applications, consumer goods, radio-frequency modems and similar applications where high performance filters are required. Rabinovich said before this product was available, typically designers had to resort to making the filter networks themselves using discrete elements such as capacitors, inductors. We’re happy to sell those capacitors and inductors to the engineering companies that build them. However, the amount of board space consumed, and variability of the placement of components on a PC board resulted in a filter performance that is unlike what you see from MLO filters,” Rabinovich said.