Proceedings of Asia-Pacific Microwave Conference 2007

Reconfigurable Circuits and Architectures for

Wireless SystemsTauno Vaha-Heikkila and Pekka Rantakari

'MilliLab, VTT, P.O.BOX 1000, 02044 VTT, Finland, tauno.vaha-heikkilagvtt.fi

Abstract - Reconfigurable circuits based on tunable orswitchable elements are shown in this presentation. Thesekind of circuits are the base for tunable, adaptive, frequencyagile as well as for reconfigurable systems. This presentationcovers examples of tuning element, reconfigurable circuitsand architectures.

I. INTRODUCTION

Present and future wireless systems have need forlowering system cost, improving performance andflexibility, tolerating deviation in manufacturing, andintegrating the whole system to smaller volume andhaving more functionalities. Handset applications aregood example of these kinds of products. For example,handset phones should be operational at all continentseach having own frequency allocations and otherstandards, more functionalities should integrated to asmaller volume, several applications with different radiosneed to be included, and the price should be lowered. Toreach these goals, reconfigurable circuits andarchitectures are needed. Other applications with similarrequests include base stations, radio links between basestations and multifunctional radars. From the frequencypoint of view, applications cover roughly from 0.5 GHzto 100 GHz. RF MEMS is seen one of the enablingtechnologies to achieve large tunability, high linearity,low loss, wide frequency coverage, and low cost in massproduction.

II. RECONFIGURABLE FRONT-END ARCHITECTURES

Traditional multi-band front-ends have several radios,often one radio for each frequency band. An other optionis to use wideband components and antennas thuslowering the system cost. A drawback of the widebandsolution is that the performance of the system is usuallylower compared to an optimized solution because in theoptimized solution more gain can be achieved with lowernoise figure. A possible solution is to use reconfigurablecircuits like reconfigurable matching networks togetherwith amplifiers, antennas and other building blockswhich need tunability. Fig. 1 shows examples of atraditional and reconfigurable front-ends.

Antennas can also be made reconfigurable by havingelectrical beam steering and adaptive antenna elements.Fig. 2 presents schematically a possible reconfigurablefront end. The SPDT switch can be replaced with a

tunable filter or tunable diplexer if the receiver andtransmitter need to be used at the same time.

ANTENNA

MATCHING TUNABLENETWORK FILTER

LNA

POWE /ANTENNA ANTENNAA S/ENSOR TUNER

MATCHING MATCHINGNETWORK NETWORK

Fig. 1. a) Schematic of a traditional multi-band front-endwith multiple radios and a wideband antenna. b) Reconfigurablefront-end with reconfigurable building blocks.

Fig. 2.Reconfigurable front-end having reconfigurableRx/Tx chains and reconfigurable phased array antenna.

III. RECONFIGURABLE MATCHING NETWORKS

Operation frequencies of building blocks in radios arefixed and the performance of the building blocks areoften optimized with matching networks. By makingthese tunable, the whole RF front-end can be tuned.Reconfigurable matching networks and tuning circuitsare well suited for example for LNAs, PAs, antennas,oscillators, and filters [1-8]. Fig. 3 shows an example of a

1-4244-0749-4/07/$20.00 @2007 IEEE.

reconfigurable 20-60 GHz matching network for multi-band radio links and radars [4]. It has been realized withRF MEMS technology.

CMAM2X5 mm

(a)

x hANTENNA

MATCHINGNETWORK

(b)

0 10 20 30 40

Frequency (GHz)

I II 0.50

1

0.25o

10 Q Load-- Loss

Sil

0.0050 60

(c)

Fig. 3. a) Photograph of an 8-element 20-60 GHzreconfigurable matching network for power amplifiersb), and c) matching of a 10 Q load (PA output) to 50 Q(antenna input) with the matching network at multiple[4].

VI. CONCLUSION

Reconfigurability is seen one of the most importantways to improve current and future radio front-ends.Special session presentation focuses to architectures,circuits and technologies used in reconfigurable front-ends.

REFERENCES

[1] T. Vaha-Heikkila and G. M. Rebeiz, "A 4-18 GHzReconfigurable RF MEMS Matching Network For PowerAmplifier Applications," International Journal of RF andMicrowave Computer-Aided Engineering, vol. 14, no. 4,pp. 356-372, 2004.

[2] T. Vaha-Heikkila, K. Van Caekenberghe, J. Varis, J.Tuovinen, and G.M. Rebeiz, "RF MEMS impedancetuners for 6-24 GHz applications," International Journal ofRF and Microwave Computer-Aided Engineering, vol. 17,no. 3, pp. 265-278, 2006.

[3] T. Vaha-Heikkila, J. Varis, J. Tuovinen, and G.M. Rebeiz,"A 20-50 GHz RF MEMS Single-Stub Impedance Tuner,"IEEE Microwave and Wireless Components Letters, vol.15, no. 4, pp. 205-207, 2005.

[4] T. Vaha-Heikkila and G. M. Rebeiz, "A 20-50 GHzReconfigurable Matching Network for Power AmplifierApplications," IEEE MTT-S International MicrowaveSymposium digest, Forth Worth, TX, USA, pp. 717-721,2004.

[5] T. Vaha-Heikkila, J. Varis, J. Tuovinen, G. M.Rebeiz, "A V-Band Single-Stub RF MEMSImpedance Tuner", Proceedings of EuropeanMicrowave Conference 2004, Amsterdam,Netherlands, pp. 1301-1304, 2004.

[6] T. Vaha-Heikkila, J. Varis, J. Tuovinen, G. M.Rebeiz, "W-Band RF MEMS Double and Triple-Stub Impedance Tuners," 2005 IEEE MTT-SInternational Microwave Symposium digest, LongBeach, CA, USA, 2005, pp. 923-926.

[7] Q. Shen and N.S. Barker, "A reconfigurable RF MEMSdouble slug impedance tuner," Proceedings of the 35thEuropean Microwave Conference, Paris, France, 2005, pp.537-540.

[8] T. Vaha-Heikkila and M. Y1onen, "CMOSCompatible Switched MEMS Capacitors Up to 220GHz Applications," Proceedings of the 36thEuropean Microwave Conference 2006, Manchester,UK, 2006, pp. 1060-1063.