imec, Heverlee, Belgium 2 Vrije Universiteit Brussel, Brussels, Belgium

Transcription

1 A Dual-Frequency 0.7-to-1GHz Balance Network for Electrical Balance Duplexers Benjamin Hershberg 1, Barend van Liempd 1,2, Xiaoqiang Zhang 1, Piet Wambacq 1,2, Jan Craninckx 1 1 imec, Heverlee, Belgium 2 Vrije Universiteit Brussel, Brussels, Belgium 1of 33

2 Motivation Mobile RF frontends use SAW filters and RF switches to support FDD iphone 6s 19 FDD-LTE bands GHz Cost Area Performance 2of 33 2

3 Background: Electrical Balance Duplexer PA Antenna Z ANT Antenna Tuner FDD operation requires that: 1) EBD blocks PA signal at f TX 2) EBD blocks PA noise at f RX path 1 path 2 LNA Z BAL Mikhemar, ISSCC 2009 van Liempd, ISSCC of 33

4 Background: Electrical Balance Duplexer PA Antenna Z ANT Antenna Tuner FDD operation requires that: that: 1) EBD cancels blocks PA PA signal signal at f TX at f TX 2) 2) EBD cancels blocks PA PA noise noise at f RX at f RX path 1 LNA path 2 Z BAL 4of 33

5 Background: Electrical Balance Duplexer PA Antenna Z ANT Antenna Tuner FDD operation requires that: that: 1) EBD cancels blocks PA PA signal signal at f TX at f TX 2) 2) EBD cancels blocks PA PA noise noise at f RX at f RX path 1 LNA path 2 Z BAL this work balance network 5of 33

6 Key Challenge The antenna impedance is Frequency dependent Time dependent Z BAL must track these variations at both f TX and f RX 6of 33

7 Tuning Spec: region TX region TX region RX Z ANT (f TX ) Impedance-variation coverage region of Z BAL at f Z ANT (f TX RX ) 0 0 Z 0TX Antenna tuner can reduce the required size 7of 33

8 Tuning Spec: region TX region TX region RX Z ANT (f TX ) 0 0 Z 0TX Described by a pair of values: 1) the center impedance Z 0TX (Ω) 2) the perimeter of region TX (VSWR) Z ANT (f RX ) 8of 33

9 Tuning Spec: region RX region RX Z ANT (f TX ) 0 Z 0TX Drift Q BW -1 Z ANT (f RX ) Hypothetical antenna impedance (Z ANT ) across frequency 9of 33

10 Tuning Spec: region RX region RX Z ANT (f TX ) 0 Z 0TX Z ANT (f RX ) Described by: 1) max rate of impedance change allowed for Z ANT (% / MHz w.r.t. f ref ) 10 of 33

11 Tuning Specs: region TX & region RX The balance network can synthesize all impedances in region TX at f TX and simultaneously generate any impedance in region RX at f RX. 11 of 33

12 Dual-Frequency Tuning Concept High-level perspective 12 of 33

13 Dual-frequency tuning concept Core idea: Make certain tuning knobs only influence Z BAL at f 1 and not at f 2 Z TUNE Z BAL (f) f 1 f 2 High-Q Tunable Frontend Impedance Filter Z TUNE High-Q Tunable Backend Impedance 13 of 33

14 Dual-frequency tuning concept Core idea: Make certain tuning knobs only influence Z BAL at f 1 and not at f 2 Z TUNE Z BAL (f) f 1 f 2 High-Q Tunable Frontend Impedance Filter Z TUNE High-Q Tunable Backend Impedance Reduced Tuning Complexity Influences both Z BAL (f 1 ) and Z BAL (f 2 ) Only influences Z BAL (f 1 ) 14 of 33

15 Dual-frequency tuning concept Full Region RX Coverage For each Z BAL (f 2 ) set here......a wide range of Z BAL (f 1 ) s can be set here Z TUNE Z BAL (f) f 1 f 2 High-Q Tunable Frontend Impedance Filter Z TUNE High-Q Tunable Backend Impedance Reduced Tuning Complexity Influences both Z BAL (f 1 ) and Z BAL (f 2 ) Only influences Z BAL (f 1 ) 15 of 33

16 Circuit Implementation Practical application of theory 16 of 33

17 Circuit Implementation Z BAL Distributed implementation of conceptual blocks Efficient, flexible approach Uses only high-q reactive elements Maximizes frequency dependency Must still synthesize impedances in vicinity of 50Ω 17 of 33

18 Guaranteed low-pass filtering A stage circuit B Stages 1-5 resonance always > 1GHz. Guarantees low-pass characteristic in-band Stages 6-9 resonance can be < 1GHz Needed to fully cover all parts of region RX 18 of 33

19 Accumulated filtering across stages f TX Z BAL (f TX ) Z BAL (f RX ) Z BAL Z f RX C 1 L 1 St age 1 Stage 2 Stage 3 St age 4 Stage 5 Stage 6 St age 7 Stage 8 Stage 9 Due to filtering, Z BAL (f RX ) doesn t see the latter stages but Z BAL (f TX ) does. 19 of 33

20 Tunable capacitors A Digitally controlled banks 6 stacked SOI switches for power handling Additional drain-source capacitors for improved offstate voltage equalization 20 of 33 B

21 Custom Simulation Engine C 2 C 4 C 6 C 8 C 10 C 12 C 14 C 16 C 18 Z BAL L 2 L 3 L 4 L 5 L 6 L 7 L 8 L 9 L 10 C 1 L 1 C 3 C 5 C 7 C 9 C 11 C 13 C 15 C 17 C 19 What are the optimal component values? How do we validate for region TX, region RX? 21 of 33

22 Custom Simulation Engine Brute-force design and validation Typical design iteration 50 million balance network settings < 2 minutes Final validation 100 billion balance network settings approx. 2 days 22 of 33

23 Measurement Results 23 of 33

24 Chip Photo GSG Input Pad 8.28 mm 2 (3.6 mm x 2.3 mm) 24 of 33

25 Measured Tuning Capability Technology Chip Area Operating Range Region TX Region RX LTE Bands Validated 0.18μm RF SOI CMOS 8.28mm 2 (3.6mm x 2.3mm) 0.7 GHz 1.0 GHz 1.1:1 VSWR, 54+j5Ω 1.2%/MHz (w.r.t. 800MHz) 5, 6, 8, 12, 13, 14, 17, 18, 19, of 33

26 Single Frequency Tuning Range Z BAL range at 700 MHz Z BAL range at 800 MHz Z BAL range at 900 MHz Z BAL range at 1 GHz 26 of 33

27 region RX for Z BAL (f TX ) = Z 0TX f TX = 835 MHz f TX = 880 MHz f TX = 835 MHz f TX = 870 MHz f TX = 890 MHz f TX = 940 MHz Band 5 Band 6 Band 8 f TX = 709 MHz f TX = 738 MHz f TX = 782 MHz f TX = 750 MHz f TX = 793 MHz f TX = 763 MHz Band 12 Band 13 Band of 33

28 region RX for Z BAL (f TX ) = Z 0TX f TX = 710 MHz f TX = 740 MHz f TX = 822 MHz f TX = 867 MHz f TX = 837 MHz f TX = 882 MHz Band 17 Band 18 Band 19 f TX = 847 MHz f TX = 805 MHz Band of 33

29 Tuning Algorithm in Matlab 29 of 33

30 Tuning Efficiency Histogram Algorithm search efficiency # of Trials mean = 479 σ = 605 max = 4304 Outliers due to finite resolution of tunable capacitors. Easily fixed. Iterations until solution is found (per trial) 30 of 33

31 Conclusion First generic dual-frequency balance network Z ANT /Z BAL co-design specifications Region TX, Region RX Efficient tuning algorithm demonstrated for search space of 2 x of 33

32 32 of 33