EPCOS has developed miniaturized SAW connectivity multiplexers that support the most important wireless services and transmission protocols. Thanks to these new components, even more functions can now be implemented in mobile phones within their usual compact dimensions.
Whereas mobile phones used to be used exclusively for telephony, they now offer a wide range of additional services and support various transmission protocols. The associated wireless technologies are subsumed under the term connectivity, and also known as complementary wireless technologies.
About half the mobile phones manufactured today feature FM receivers and Bluetooth (BT) interfaces. GPS and WLAN are now standard in smart phones. Within the next few years, GPS and WLAN are also expected to be widely used in mobile phones of the mid-price class (Fig. 1).
| | FIGURE 1: EXPECTED CONNECTIVITY PENETRATION IN MOBILE PHONES |
In addition to Bluetooth and FM radio, GPS will also reach substantial penetration rates in mid-range mobile phones. |
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The major manufacturers of ICs for these wireless connectivity technologies are offering combo ICs that support multiple connectivity standards integrated in a single chip . These combo ICs not only save costs, but can also be used to significantly reduce the dimensions of the connectivity solution.
The combo ICs recently launched on the market by semiconductor manufacturers most frequently offer the following combinations:
- BT + FM,
- BT + FM + GPS,
- BT + FM + WLAN
Beyond this, some leading chipset suppliers have already embedded GPS and BT as standard functions in their cellular transceiver ICs.
In addition to IC integration, further size reduction potential can be further exploited in the sector of frequency filters and RF front ends. This can further reduce the number of components and thus simplifies the connectivity solution.
For this purpose, EPCOS is developing multiplexers for SAW filters (SAW multiplexers) allowing multiple filter functions to be integrated in a single component. Fig. 2 shows a multiplexer for the integration of GPS and BT. The GPS-BT duplexer LU33 in case size 2016 from EPCOS combines two SAW filters for GPS and Bluetooth as well as the diplexer that multiplexes these two filters to a single antenna output. This integration reduces the number of necessary discrete filter blocks as well as their space requirement. The costs of an additional antenna can also be saved. In addition, the number of required solder points on the circuit board is reduced, so that placement costs drop and the MTBF rises.
| | FIGURE 2: BLOCK DIAGRAM OF AN INTEGRATED FILTER SOLUTION |
The integration of the BT and GPS filters as well as a multiplexer in a single module reduces the number of components and allows one antenna to be saved. |
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The new duplexers for wireless connections use the same proven LTCC technology as the EPCOS duplexers for cellular communications. The duplexer contains three basic functions in a single package: two SAW filters and a diplexer. The latter is a frequency divider that splits the antenna signal up between the two frequency bands supported by the duplexer.
Fig. 3 shows the basic configuration of a BT-GPS duplexer. The duplexer contains a 2in1 chip so that two filter functions are combined in a single SAW chip. The LTCC substrate also integrates the impedance matching elements for the SAW filters as well as the ESD protection needed at the antenna input to prevent potential destruction of the SAWs. The SAW multiplexers are already tuned to the impedance of the transceiver and antenna, which simplifies the solution for customers. The integration of RF matching components in an LTCC substrate assures a continuously reproducible RF solution. Depending on the circuit topology, 50 to 80 percent of the circuit board space can be saved compared to previous discrete solutions.
| | FIGURE 3: BASIC CONFIGURATION OF A BT-GPS DUPLEXER |
In addition to the filter and duplexer functions, the module integrates the matching networks (MN) and the antenna-side ESD protection functions. |
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As for duplexers for cellular frequency bands, a high isolation between the multiplexed frequency bands is also important for connectivity duplexers. The GPS receiver in particular must not be disturbed by WLAN or BT transmission signals. Fig. 4 shows the attenuation curve and the good isolation of the BT and GPS paths of the LU33.
| | FIGURE 4: FILTER SELECTION CURVES OF LU33 |
The graphs show the attenuation curves of the BT path (red) and the GPS path (blue). The low insertion losses of better than 1.5 dB for GPS and better than 2.5 dB for BT ensure high receive sensitivity and low current consumption. |
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EPCOS is currently developing a new product family of SAW multiplexers to comprehensively support the combo ICs for complementary connectivity technologies in future applications. The Table gives an overview of this future product family. These new products will be applied by customers in order to simplify their discrete connectivity solutions, but will also be embedded in future fully-integrated module solutions from TDK-EPC.
The LU33 and LT36 duplexers are designed for GPS in combination with 2.4-MHz ISM band applications. They are essentially distinguished by the fact that the LU33 can handle the BT power class 1.5 (maximum Tx power of +15 dBm), while the LT36 is designed for a WLAN power of up to +23 dBm. The LU39 and LU58 modules were developed for dual-band WLAN applications. The LU39 triplexer allows GPS and both WLAN bands to be received with only one antenna. The B9100 and B7742 multiplexers are suitable for use with cellular transceivers in which GPS has already been integrated.
TABLE: THE SAW MULTIPLEXER PRODUCT FAMILY FOR COMPLEMENTARY WIRELESS CONNECTIVITY APPLICATIONS
| EPCOS part no. | Package size | Product type | Supported frequency bands |
| LU33 | 2016 | GPS-BT duplexer | GPS, WLAN LB (incl. BT) |
| LT36 | 2025 | GPS-WLAN duplexer | GPS, WLAN LB (incl. BT) |
| LU39 | 3025 | GPS-WLAN triplexer | GPS, WLAN LB (incl. BT), WLAN HB |
| LU58 | 2016 | WLAN duplexer | WLAN LB (incl. BT), WLAN HB |
| B9100 | 2025 | GPS cellular triplexer | GPS, Cell LB, Cell HB |
| B7742 | 2025 | GPS cellular extractor | GPS, Cell LB, Cell HB |
| GPS | 1571 MHz |
| WLAN LB | 2400 to 2500 MHz |
| WLAN HB | 5150 to 5850 MHz |
| Cell LB | 800 to 900 MHz |
| Cell HB | 1800 to 1900 MHz |
Authors:
Dr. Patric Heide, Director Complementary Wireless Solutions
Bernardo Knoblich, Product Marketing Manager for Connectivity SAW Products
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