Murata Shrinks Further Isolator to Fit Today\'s Mobile Phones
Category: Telephone, cellular phone and intercom
Manufacture: Murata Manufacturing Co.
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Murata Shrinks Further Isolator to Fit Today's Mobile Phones
owadays, the adoption of International Mobile Telecommunications 2000 (IMT-2000) standard for 3G mobile phones is advancing. Under the IMT-2000 banner, the use of the Wideband Code Division Multiple Access (W-CDMA) system in particular is spreading in Japan and Europe. This shows the ongoing evolution of mobile communication standards from one generation to another. The recent hike in transmission rate and multiplication of functions in mobile phones resulted in an increase in the number of components and current consumption. Moreover, a review of the number of frequency bands used for mobile phones reveals that there should be a switch from conventional dual-band to triple-band in order to meet the rise in demand for mobile phone services. This change will increase the number of mobile phone components further. Given the circumstances, there are now stronger requirements for radio frequency (RF) components of mobile phones to become more miniaturized, thin, lightweight and efficient to bring down current consumption. To meet these requirements, Murata Manufacturing Co. Ltd. had developed the CES20 series. The low-profile isolators serve in 2GHz-band mobile phones.
Fig. 1: RF circuit block diagram
How Isolators Work World's Smallest An isolator passes signals The CES20 series meain the forward direction. It sures 3.2 × 2.5 × 1.2mm blocks the signals in the re(maximum height) (L × W verse direction. × H). Its volume is about The isolator mainly works 60 percent of that of Muin the internal RF unit of a mo- CES20 series 2GHz-band rata's CES30 series (conbile phone. Fig. 1 shows a isolator for W-CDMA ventional model), which block diagram for a general equipment measures 3.2 × 3.2 × RF unit. 1.6mm (maximum height) A human body near an antenna of a mo(L × W ×H). The CES20 is the world's smallest isolator bile phone causes the antenna impedance that complies with 2GHz-band W-CDMA. to fluctuate remarkably. This fluctuation With its compact profile, the CES20 has a mass causes reflection of some of the signals of 0.034g, which is about half that of convenoutput from the power amplifier at the antional model (Fig. 2). tenna and their return to the power amplifier. The reflected signals have adverse Design Approaches effects, such as lowering the power load Fig. 3 shows sample electric characefficiency and generating unnecessary sigteristics of the 2GHz-band isolator for Wnals, for example, adjacent channel inCDMA phones. The 2GHz-band isolator terference waves. Placing an isolator afhas achieved an insertion loss of 0.5dB ter the power amplifier can reduce the efmaximum (merit value: 0.40dB) and an fective load fluctuation in relation to the isolation of 14.5dB minimum (merit value: power amplifier output at the occurrence 16.5dB) in the frequency band from of antenna impedance fluctuations. 1,920MHz to 1,980MHz at normal temThus, using an isolator can prevent lowperatures, which are equivalent of the elecering of efficiency of power amplifier. It tric characteristics of the conventional also reduces current consumption and model. The isolator has also achieved a lengthens duration of voice calls. Use of VSWR of 1.25 maximum (merit value: the isolator can also reduce the adjacent 1.10) at input (return loss1: 19.1dB minchannel power ratio (ACPR). imum). The CES20 series has realized a miniature, low-profile design while maintaining the electric characteristics of the conventional model. Similar to the conventional model, the CES20 series features a wideband of input reflection characteristic and the reduction of input reflection fluctuations. Fig. 4 shows the waveform charts for comparison of electric characteristics between the CES20 series and conventional model. Fig. 5 shows the input impedance fluctuations of the CES20 series, the CES30 series, and the CE040 series for comparison. The graphs in Fig. 5 plot the impedance in the passing band (low frequency of 1,920MHz, center frequency of 1,950MHz, and high frequency of
Copyright 2006 Dempa Publications, Inc.
Fig. 2: Structure of the CES20 series isolator
1,980MHz) of the 2GHz-band isolator for W-CDMA phones. The wideband of input reflection characteristic and reduction of input reflection fluctuations greatly improve the impedance matching to the power amplifier placed at the input to the isolator. The impedance-matching performance of the isolator results in the reduction of current consumption in the RF transmission system and contributes to the longer voice calls. Changing Materials To realize the horizontal dimensions of the CES20 series, Murata reduced the size of the ceramic multilayer circuit board by about 80 percent from the conventional size. To ensure the same level of impedance-matching performance as that of the conventional model with the limited area of circuit board, Murata employed a new material that provides higher specific inductive capacity than that of the conventional material of ceramic multilayer circuit board. The new material also has higher capacitance (Q) than that of the conventional material, and largely contributes to the reduction of losses of the isolator. Meanwhile, to realize the height of the CES20 series, Murata reduced the thickness of the magnet. Since simple reduction of magnet thickness would disable the application of sufficient operating magnetic field to the ferrite, the company used a new material for the magnet, one that provides an enhanced maximum energy product (BH max). These two improvements led Murata to realize the world's smallest isolator. Environmentally Sound Components for mobile phones are subject to increasingly strict requirements for environmental protection. These include the restriction in the use of hazardous substances and the adoption of
Copyright 2006 Dempa Publications, Inc.