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Agilent Technologies Announces High-Performance FBAR Filter for U.S. PCS Band Mobile Phones and Data Cards

Miniature CDMA Component Allows OEMs to Simplify Designs and Reduce Board Space

The manufacturer says . . .

ChipCenter's Paul O'Shea says . . .

Agilent Technologies Inc today introduced the ACPF-7001, a transmit filter, based on its film bulk acoustic resonator (FBAR) technology, for U.S. PCS band products, which include code division multiple access (CDMA) mobile phones and data cards. The new transmit filterıs small size and high performance allows original equipment manufacturers (OEMs) to simplify designs and reduce component counts. ıOur new high-performance FBAR transmit filter significantly reduces board space, creating room to add several next-generation features, while maintaining the cell phoneıs compact size,ı said Bryan Ingram, vice president and general manager of Agilentıs Wireless Semiconductor Division. ıAgilentıs revolutionary FBAR product family gives our OEM customers the size and performance advantage they need to differentiate their products.ı The Agilent ACPF-7001 is a full-band transmit filter for U.S. PCS Tx band applications (1850-1910 MHz). In typical CDMA cell phone architectures, the transmit filter is incorporated between the driver amplifier and the power amplifier to reduce noise in the receive band, enhancing receiver sensitivity. The high rejection capability of Agilentıs miniature FBAR transmit filter keeps unwanted signals out of the receiver, while its low insertion loss increases transmitter efficiency. Todayıs CDMA handset designs typically use two SAW (surface acoustic wave) split-band filters -- 1850-1880 MHz and 1880-1910 MHz -- that are selected via a radio-frequency switch. Their footprint measures 5 mm x 12 mm. By comparison, the Agilent ACPF-7001 FBAR full-band transmit filter eliminates the need for a second filter, a switch and associated passive components, and measures only 3 mm x 3 mm. This dramatic space savings reduces the printed circuit board area required for the transmit filter by up to 80 percent, lowering manufacturing costs and eliminating the need for interface design and programming. The ACPF-7001 FBAR full-band transmit filter provides 3.5 dB maximum insertion loss over the 1850-1910 MHz transmit band and 33 dB minimum attenuation (40dB typical) over the 1930-1990 MHz receive band. The filterıs high rejection allows the use of a lower IP3 receive chain, thus saving current. The FBAR filter is specified over the -30 degrees C to +85 degrees C temperature range. The Agilent ACPF-7001 is the newest member of Agilentıs growing FBAR family. Agilentıs HPMD-7904 and HPMD-7905 miniature FBAR duplexers measure only 5.6 mm by 11.9 mm by 2 mm and have a 50 to 80 percent smaller footprint than conventional ceramic duplexers. They have been designed into more than 20 cell phone platforms, and numerous expansion cards for PDAs and laptop computers. Agilentıs FBAR products are part of the companyıs CDMAdvantage RF chipset, which includes key RF functions required for 800 MHz and 1900 MHz handsets. CDMAdvantage uses Agilent second-generation PHEMT (pseudomorphic high-electron-mobility transistor), advanced silicon bipolar, and FBAR processes to achieve a flexible, efficient and compact solution. Send reader inquiries to Agilent Semiconductor Products Group Tel: 800-235-0312; E-mail:semiconductorsupport@agilent.com Web: www.agilent.com.

Agilentıs FBAR (film bulk acoustic resonator) filter is a very simple micro electromechanical system (MEMS). It is considered a MEMS because an electrical signal causes a vibration in a membrane. When the membrane vibrates it causes a resonance that allows the pass band of interest to get through. This FBAR technology came from the well respected Agilent Labs but it was something that a number of companies have been working on for many years. Many surface acoustic wave (SAW) filter manufacturers were working on this same technology because it looked promising. The Agilent ACPF-7001 is a full band transmit filter for US PCS. It is a filter with a frequency that is not tunable so the Agilent had to pick a frequency that would enable them to ramp to high volume quickly, and one that customers wanted, so they chose US PCS. They fully expect to add GSM and high frequency filters in the future. The ACPF-7001 PCS product has an impressive 3.5dB maximum insertion loss, which allows more of the desired signal to get through without much loss associated to it. Insertion loss of other filters is typically in the 4.5 to 5dB range. These competitors are using a SAW technology, typically Lithium Tantalum-based. The Agilent filter provides 33dB attenuation outside the pass band, which is where you want it. It is important because the filter is on the input side of the power amplifier and that means the signals youıre trying to eliminate donıt get into the power amplifier - and donıt get amplified. You can imagine what would happen if they did. You would have an isolation problem between the receive and transmit sides because the power amp would be blasting all the additional unwanted bandwidth and it would couple over to the receive side. Then you would need a higher value third-order intercept point (IP3) component on the receive side, to make up that loss of dynamic range. That means more expensive parts that consume more current. By doing this filtering prior to the power amp, Agilent removes those components, the signals arenıt amplified, and they arenıt strong enough to couple over to the receive side. Thatıs a key point; the high rejection, very good attenuation prevents those parts from leaking over to the receive side. You may wonder how it is the filters high rejection allows the use of the lower third order intercepts IP3 points. You have to envision a block diagram where you have an antenna, and coming in from the antenna on the receive side is an LNA amplifier and some filtering. On the transmit side there is a power amplifier as the last component before it goes through the duplexer out to the antenna. If you amplify the whole signal then all the unwanted signal would be amplified (and there are some very strong signal strengths) and you wouldnıt be able to make the phone large enough to separate your transmit and receive chain to prevent some signal from leaking from the transmit side to the receive side. The signal bleeding over from the transmit side then raises the noise floor on the receive side. Therefore you need to use higher linearity components (higher IP3 components) to try to get back some of that dynamic range. That increases your costs because the higher IP3 parts are expensive and increases current consumption and decreases battery life. Agilentıs solution uses very high attenuation in the filter before the signal gets into the power amplifier, and eliminates the signals that should not be passed through the power amp. The unwanted signals are attenuated at a very low power level so they donıt get a chance to couple over to the receive side and donıt interfere with the incoming signals. The ACP-7001 will prove to be breakthrough technology and will have other companies running to catch up because it simplifies design, and lowers cost by eliminating a second filter, switch, and the associated path of components. The current filter design requires two SAW filters. Each SAW filter covers half the band youıre trying to pass, and a switch between them, and some other passive components like inductors, capacitors, and resistors. This design can require approximately 5mm x 12 mm. Agilentıs solution takes up only 3mm x 3mm and is placed in front of the power amp. So for new designs this Agilent product eliminates the need to have a PCB with all the components, instead you just drop in one ACP-7001 component into your design. You can do the math but it could save you a large percentage on board space. The Agilent ACPF-7001 FBAR full-band transmit filter is priced at $2.49 each in 25,000-piece quantities, quantities of a million plus units will be under $1 and are available for immediate delivery. Further information including a data sheet on Agilentıs FBAR product family is available at: www.agilent.com/view/fbar.

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