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REVIEW: Antenna-routing hybrid endows cellular–plus-PCS handsets with GPS

Avago Technologies' New FBAR-based Quintplexer Brings Single Antenna, Simultaneous GPS and Voice to Mobile Handsets

Company's FBAR Shipments Surpass 500 Million

SAN JOSE, Calif.—Avago Technologies announces a new quintplexer module delivering superior global positioning system (GPS) performance levels. The company is a leading supplier of analog interface components for communications, industrial and consumer applications. Avago's highly integrated and compact ACFM-7102 quintplexer delivers a significant improvement in insertion loss while delivering high GPS to cell band, and GPS to PCS band isolation. With a unique, switchless design to optimize performance, the FBAR-based ACFM-7102 provides designers with flexibility and simplicity when creating ultra-small, high-performance mobile phones that deliver simultaneous GPS functionality.

Avago also surpasses a significant milestone for its award-winning film bulk acoustic resonator (FBAR) product line. The company has shipped more that 500 million FBAR-based filters. “We're very pleased to report that shipments of our FBAR products have nearly doubled in the past 18 months,” said Philip Gadd, Senior Marketing Director for Avago Technologies' wireless semiconductor division. “FBAR clearly delivers the performance and flexibility that is ideal for next-generation handset phones. And, the introduction of the FBAR-based ACFM-7102 module continues with our focus on dramatically expanding this successful quintplexer platform to meet the needs of our customers.”

A 1.5 dB insertion loss in its GPS filter path gives the ACFM-7102 superior performance levels for concurrent GPS operation. The ACFM-7102 also delivers excellent GPS to cell transmitter and GPS to PCS transmitter isolation enabling single antenna simultaneous GPS operation and delivering excellent GPS sensitivity. By fully integrating the GPS filter with cell and PCS duplexer into one small module, the ACFM-7102 enables the development of single antenna dual-band, simultaneous GPS handsets that are thinner, with longer overall battery life and improved performance. Avago's ACFM-7102 is also ideal for small PC cards, PDAs and other dual-band wireless devices.

Utilizing Avago's FBAR filter process and innovative Microcap bonded-wafer chip scale packaging technology, the ACFM-7102 is available in a small 5 mm by 8 mm by 1.2 mm thick module. Avago's quintplexer module operates in -30 degrees C to +85 degrees C and is compatible with CDMA and WCDMA third generation (3G) technology that supports voice, data, images, and video communications at speeds up to 2Mb/s.

Pricing and Availability

Avago's ACFM-7102 is currently in limited release. Pricing starts at under $4.00 in small quantity. General availability is scheduled for Q307.

Avago Technologies 's so-called quintplexer module is based on LC matching networks to impedance-match the company's FBAR (film bulk acoustic resonator) duplexers with an FBAR-based GPS (Global Positioning System) filter. The resulting magic is that your design's single antenna can now feed, and be fed from, five ports.

Most duplexers, as three-port devices, provide a transmitting port, a receiving port, and an antenna port. Duplexers provide necessary RF I/O connections, yet prevent a cellphone's transmitter signals from being reflected from the antenna back to the input of a cellphone's receiver. If that happens, the powerful local RF signal overloads and blocks the receiver's front-end.

Duplexers Are Too Big

In essence, duplexers enable simultaneous two-way RF transmissions. But, duplexers are usually among the largest components in today's midget cellphone handsets. They crowd out board real estate that could otherwise be used to add differentiating features.

For that reason, FBAR-based duplexers—significantly smaller than predecessor ceramic duplexers—have gained favor in recent years. FBAR duplexers enhance your ability to craft smaller and slimmer feature-rich handsets.

Agilent Technologies was one of the first companies to devise and implement FBAR devices (and Avago is an Agilent-spawned company). Agilent's first-generation FBAR duplexers, now found in more than 80% of handsets designed for PCS (Personal Communications Service) usage, are about a quarter of the size of forerunner ceramic duplexers.

Chip-Scale Packaging

To reduce the size of FBAR packages even more, Agilent built its FBAR duplexers with bonded-wafer CSP (chip scale packaging). CSP techniques permit Agilent to render ultra-small filters in hybrid MCOB modules (molded-chip-on-board) that were less than a tenth the volume of ceramic devices.

There were drawbacks to FBAR filters, though, especially with phase shifters composed of lumped inductors and capacitors or quarter-wave transmission lines that served as impedance matching elements. These phase shifting circuits introduced nasty parasitic effects, and wound up increasing the size of the duplexers.

Ladder Filter Structures

To overcome these adverse effects, Avago's FBAR duplexer chips use innovative ladder-type filter structures. Auxiliary inductors are used to tune the passband bandwidth, sharpen the rolloff in the guard bands, and increase attenuation in the stopbands.

Avago's MCOB hybrid device continues where Agilent left off. Avago's FBAR filter chips on the ACFM-7102 hybrid substrate, are ladder filters with grounded-optimized inductors connected to shunt resonators. This approach shifts the poles and zeroes of the filters, stretching bandwidth to lower insertion loss. It also spreads the transmission zeroes across the rejection bands.

The technique also permits using the lowest possible coupling coefficient. Lower piezoelectric coupling coefficients permit thinner layers to be used in a network's capacitors, giving higher capacitance. That, in turn, makes for smaller resonators (at a given impedance), and makes the dice smaller.

Look Ma, No Switches

In an application, an ACFM-7102 can eliminate physical switches or MEMS (micro-electro-mechanical systems) switches, and do that with low insertion loss. In fact, the performance of these devices surpass typical SAW (surface acoustic wave) duplexers and a diplexer—and permit simultaneous GPS and CDMA (Code Division Multiple Access) in cellphone transceivers.

Melding the GPS filter with the cellphone duplexer, Avago's ACFM-7102 quintplexer will let you more easily craft a single-antenna dual-band simultaneous GPS handset. Typical receiver sensitivity will be about -110-dBm (710-nV) on the PCS band, and slightly better at cellband frequencies. This improved performance may even let you deploy an internal antenna.

Especially exciting is the ability of the ACFM-7102 to handle simultaneous GPS and CDMA RF. The device permits reception of very weak GPS signals in the presence of a cellphone's relatively strong RF output.

Saving Real Estate

This is possible due to low insertion-loss at the GPS frequencies, and very high rejection for the handset's transmitted RF. This is done without gobbling already scarce board real-estate with the likes of diplexers, triplexers, switches, additional antennas, or discrete component lumped LC networks.

Within the ACFM-7102 device, an LC network at the PCS Tx port boosts isolation at 1.575-GHz to over 50-dB. The inductors in the system are implemented as circuit board traces, and the capacitors are chip caps on semi-insulating GaAs (gallium arsenide) substrates.

It's worth noting that Avago's press release (on the left) indicates the ACFM-7102 is only available in limited quantities, although, to its credit, the company posts a less-than-$4 price point, in small quantities. As you'd expect, the datasheet for the ACFM-7102 is also preliminary. Notably, it does reflect most worst-case specs for the device.

Impressive Specs

Nonetheless, the ACFM-7102 boats some impressive specs that should be a boon to GPS-location-sensitive handset designers that adopt it. For one thing, it will handle +33-dBm of transmit power. That's a hefty 2-W of RF, which is nothing to sneeze at

The GPS filter, with a passband extending from 1.574-GHz to 1.576 GHz, exhibits an insertion loss of no more than 2-dB, yet it provides at least 45-dB of isolation to the PCS transmitted signal.

The ACFM-7102's receive cellular duplexer, with a passband from 869-MHz to 894-MHz, exhibits a maximum insertion loss of 3.6-dB. Noise blocking is at least 37-dB. The transmit duplexer counterpart, working from 824-MHz through 849-MHz, has a 2.6-dB maximum insertion loss, with 50-dB of interference blocking.

For its part on the ACFM-7102, the PCS receive duplexer, working from 1.93-GHz to 1.989-GHz, shows an insertion loss of 4.4-db at most, with a 40-dB minimum noise blocking spec. The PCS transmit duplexer operates from 1.85-GHz to 1.909-GHz. It shows an insertion loss of 3.9-dB maximum, and a 50-dB minimum of interferer blocking.

Longer Run Times

These specs reveal that the ACFM-7102 can likely reduce the demands on your transmitter's RF power output. That, in turn, can spell longer run times from already diminutive battery packs. Receiver sensitivity and dynamic range can also likely be enhanced, for boosted reception capability.

Avago seems to have succeeded in creating a fingernail-sized device comprising an ultra-low insertion-loss quintplexer. The company lays claim to a size-reduced and cost-reduced component based on high piezoelectric coupling coefficients in its FBAR structure, and very high resonator Q that permits the use of thin piezoelectrics.

High specific capacitance also lets Avago keep its multiplexer impedance-matched to 50-ohms, while maintaining minimum FBAR areas required to ensure reasonably low die cost.

As I mentioned above, the device's antenna matching network provides improved out-of-band attenuation compared to the duplexers and filter used, supporting a design with better insertion-loss/attenuation tradeoffs. A high level of integration permits 1-dB better handset sensitivity (at -110-dBm), and longer battery life than designs using the same duplexers as standalone components. Shorter handset design time can result from guaranteed good performance in a larger piece of a radio.

Unfortunately, no datasheets have been posted on the company's Web site at this time. But, you should be able to get more preliminary details by contacting Avago Technologies, 40 Shattuck Rd., Andover, Mass. Phone: 800-235-0312. E-mail: support@avagotech.com. Or, contact Avago at 350 West Trimble Rd., San Jose, Calif. 95131. Phone: 800-235-0312.

Avago Technologies , 800-235-0312, www.avagotech.com

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