Frequency Agile Ferroelectric Filters, Power Dividers, and Couplers

Transcription

1 Workshop WMA Frequency Agile Ferroelectric Filters, Power Dividers, and Couplers International Microwave Symposium 2009 R. Weigel and E. Lourandakis

2 Outline Motivation Tunable Passive Components Ferroelectric Varactors Frequency Agile Filters Frequency Agile Power Dividers & Couplers Prototype Implementation & Results Reconfigurable Amplifier Concept Conclusion & Outlook 2

3 Motivation Motivation Increasing number of communication bands Additional wireless services, e.g. GPS, WiMAX Demand for reconfigurable front-end solutions 3

4 Ferroelectric Materials - BST Nonlinear response to E field variation Tunability of 60% at 20V Voltage and temperature dependence Piezoelectric behavior 4

5 Ferroelectric Thin-Film Varactors zero bias Metal-Insulator-Metal (MIM) Compact dimensions Q around 2 GHz Acoustic resonance ADS model available bias 20V 5

6 Ferroelectric Thin-Film Varactors Single C Bias=20V C cas =n x C RF modulates capacitance RF swing is reduced by cascaded varactors Large capacitances are needed Possible for MIM capacitor Cascaded C P in =20dBm, Bias=20V 6

7 Analytical Filter Design Lowpass Chebyshev lowpass filter Analytical formulas for zero locations 7

8 Frequency Agile Lowpass Assumed tunability of 60% for BST varactors Multiband tuning from GHz Changing C results in shifted zero locations 8

9 Analytical Filter Design Notch Filter Notch filter Analytical formulas for zero and pole locations zero pole 9

10 Frequency Agile Notch Filter Assumed tunability of 60% for BST varactors Multiband tuning from GHz Changing C results in shifted zeros and poles 10

11 Analytical Filter Design Combline Filter Tuning principle Compact filter dimensions Most suitable topology Asymmetric pole allocation 11

12 Modified Combline Filter Original Second attenuation pole is shifted from DC to lower stopband Symmetric pass- to stopband transition Modified 12

13 λ/4 Based Microwave Circuits Wilkinson divider Δφ=0 deg Branch-Line coupler Δφ=90 deg Well known 3dB couplers Based on λ/4 segments 13

14 Equivalent λ/4 Segments Distributed Lowpass Quarter-wavelength segment (1) Equivalent lowpass segment (2) Comparing (1) and (2) results in Scalable equivalent circuit Signifficant size reduction 14

15 Frequency Agile λ/4 Segments Tuning of C eq shifts resonance Scalable network Slightly detuned Z Perfect phase shift Multiband function Assumed tunability of 60% 15

16 Reduced Size Tunable Wilkinson Divider equivalent lowpass Wilkinson Modified Size reduction 50% Multiband tuning Assumed tunability 60% 16

17 Reduced Size Branch-Line Coupler Branch-Line Modified equivalent lowpass Size reduction 50% Perfect phase match C eq serves as shunt element for both segments 17

18 Reduced Size Tunable Branch-Line Coupler equivalent lowpass Size reduction 50% Perfect phase shift Multiband operation with tunability of 60% for C eq 18

19 Prototype Implementation & Assembly Wire inductance Wire assemblies suffer from parasitics Flip-Chip is favorable Reduced footprint 19

20 Tunable Lowpass (1) Biasing elements Biasing components Compact dimensions Tuning range of 30% 1.5-2GHz multiband High losses due to moderate Q and RF isolation 20

21 Tunable Lowpass (2) Biasing Good agreement Increased loss due to varactor imbalances and prototype assembly Two-tone 1.95GHz with Δf=5MHz and Bias=20V 21

22 Tunable Notch Filter (1) RF-choke Cascaded varactors simplify biasing Compact design Tuning GHz Multiband operation Low losses S 21 22

23 Tunable Notch Filter (2) RF-choke Good agreement between simulation and measurement Two-tone 1.95GHz with Δf=5MHz and Bias=20V 23

24 Tunable Combline Filter (1) Good agreement Compact dimensions IL < 3dB and RL > 20dB Tuning 1.8-2GHz 24

25 Tunable Combline Filter (2) Two-tone with Δf=5MHz and Bias=5V Output 3rd order intercept point OIP3=36.5dBm 25

26 Tunable Wilkinson Divider (1) 26

27 Tunable Wilkinson Divider (2) IL < 1.2dB, Isolation > 25dB Size reduction 50% Lowpass filtering S 21,S 31 Attenuation > 20dB at 2f 0 Tuning range GHz 27

28 Tunable Branch-Line Coupler (1) Size reduction 50% Lowpass filtering at all transmission paths Attenuation > 30dB at second harmonic V Bias =5V 28

29 Tunable Branch-Line Coupler (2) V Bias =9V V Bias =15V 29

30 Tunable Branch-Line Coupler (3) Tuning range GHz IL < 2.7dB, RL > 15dB Amplitude error < 0.4dB Phase error < 5deg 30

31 System Considerations Modulated Signals Arbitrary Modulated Signal Measured QPSK Trajectory Baseband EVM Measured WCDMA Channel 3GPP WCDMA signal Specified EVM 17,5% Specified ACLR 33dB 31

32 System Balanced Amplifier Operating at transmit band f=1.95 GHz Voltage waveforms at P in =0dBm P in =0dBm 32

33 System Reconfigurable Balanced Amplifier (1) Operating at transmit band f=1.95 GHz roll-off Size reduction 50% Lowpass filtering Increased loss Bias voltage 5V Strong nonlinearities due to BST-varactors 33

34 System Reconfigurable Balanced Amplifier (2) Operating at transmit band f=1.95 GHz P in =0dBm Distortion at voltage waveforms Performance still within specification Simulated EVM < 10% Simulated ACLR ~ 35dB 34

35 Tunable coupler with 3 cascaded varactors Operating at transmit band f=1.95 GHz 3 cascaded varactors P in =0dBm P in =0dBm 35

36 Verification Tunable Branch-Line Coupler P in =10dBm Agilent PSG P in =10dBm Agilent PSA 36

37 Conclusion Conclusion & Outlook Potential of ferroelectrics in tunable front-end Reliable modeling and characterization Candidates for tunable microwave circuits Frequency agile filters Reduced size tunable dividers and couplers Prototype implementation & results Overall good agreement to simulation Outlook Integration of tunable subsystems into front-end 37