* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Design Procedure for Compact Asymmetric SPDT Switches
Survey
Document related concepts
Regenerative circuit wikipedia , lookup
Cavity magnetron wikipedia , lookup
Night vision device wikipedia , lookup
Rectiverter wikipedia , lookup
Power dividers and directional couplers wikipedia , lookup
Josephson voltage standard wikipedia , lookup
Index of electronics articles wikipedia , lookup
RLC circuit wikipedia , lookup
Microwave oven wikipedia , lookup
Opto-isolator wikipedia , lookup
Integrated circuit wikipedia , lookup
Microwave transmission wikipedia , lookup
Transcript
78 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.9, NO.1, JANUARY 2014 Design Procedure for Compact Asymmetric SPDT Switches and Full X-Band Demonstrator Mirko Palomba*, Riccardo Cleriti, Sergio Colangeli and Ernesto Limiti Università degli Studi di Roma “Tor Vergata”, Via del Politecnico, 1, 00133, Rome (IT) Tel: +39-0672597343; E-mail: [email protected] Abstract – A design procedure for asymmetric SPDT switches is proposed and validated by a MMIC demonstrator covering the full X-Band, well suited to integration in T/R modules. The demonstrator exhibits 0.7 dB and 1.6 dB insertion loss along its TX and RX paths, respectively, and 21.5 dB isolation in TX mode. Chip size is as compact as 1 1 mm2. Index Terms – asymmetric SPDT, compact MMIC, SPDT switch design, X-band. I. INTRODUCTION In the past, the best way to separate transceivers’ TX and RX chains consisted in using ferrite circulators, thanks to their low insertion loss and high isolation. Unfortunately these bulky and heavy devices could not be integrated. Therefore, an increasing interest in replacing ferrite circulators with FET-based circulators or switches resulted, thus leading to small, lightweight systems. However, although active circulators represent a valid improvement, they are typically larger than simple switches; furthermore, in particular cases (e.g., T/R modules) signal circulation along TX or RX path is mutually exclusive, and therefore an SPDT switch solution is sufficient. Several satellite systems for Earth Observation operate around 9.6 GHz, and it is therefore interesting to investigate switches operating in the X-Band. Contributions in open literature use particular techniques to null parasitic effects. Resonating two shunt FETs [1] results in 0.6 dB insertion loss and 17 dB isolation at 10 GHz. The resulting circuit is 0.675 1.15 mm2 but the performance results to be narrowband since isolation rapidly degrades with frequency. Another available technique is presented in [2, 3] by resonating FET in series connection instead of shunt devices. This approach leads again to narrowband behavior, but multi-octave performance on a single series resonated FET are achievable by introducing a resistor on the resonating arm [4]. A study about single gate FET SPDTs can be found in [5], highlighting the possibilities underlying FET resonant techniques. In this case, 0.7 dB insertion loss and 28 dB isolation was reached by a 0.76 1.78 mm2 chip. Also in this case, the circuit exhibits a narrowband behavior. In fact, at 0.9 GHz from central frequency, isolation drops down to 20 dB. A deep study about the relationship between FET’s physical parameters and its quality factor is presented in [6]: according to this study, the best isolation for a single-throw-single-pole (SPST) switch, with 1 dB insertion loss, is 50.7 dB. A power switch with 10 W capability is reported in [7]: this circuit exhibits 1 dB insertion loss and 26 dB isolation for a 4.5 3.7 mm2 chip. The bandwidth is 2 GHz around 9.5 GHz. A very small circuit is described in [8], with only 0.3 0.5 mm2 chip size, by developing the dielectric overhang gate process to reduce the distance between source and drain electrodes of the multiple-gate HEMTs used for the switch. Good performance is registered at 900 MHz but they rapidly degrade to 1 dB insertion loss and 16 dB isolation at 2.7 GHz. A high-power SPDT switch with selectively anodized aluminum substrate is reported in [9], exhibiting 1.3 dB insertion loss and 20.3 dB isolation in a 1 GHz bandwidth around 9.5 GHz; chip size is in a 4.4 3.1 mm2. A quarter-wave PIN switch architecture used for T/R modules is presented in [10], providing better bandwidth performance IJMOT-2014-1-541 © 2014 IAMOT 79 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.9, NO.1, JANUARY 2014 and small chip area occupation. Circuit behavior is asymmetric in this case. In the present contribution, the latter architecture has been considered and analytically studied. A design procedure is then proposed to properly select devices and obtain target performance. A monolithic circuit demonstrator is provided to assess the methodology effectiveness. II. THEORETICAL ANALYSIS FET T/R switch reference architecture is visible in Fig.1. Z1 represents L1 and the FET on the same branch, while Y2 includes the second FET and L2. The quarter-wavelength transformer has 50 Ω characteristic impedance. Fig.1 can be rearranged as in Fig.2: Fig.2. Rearrangement of the T/R switch scheme. To gather S31, the product of 3 ABCD chain matrixes can be computed: 1 S31 1 Z 0 Z1 0 0 j 1 Z 0 j Z0 1 0 Y2 0 1 [4] j 2 ( Z 0 Z1 ) 2 Z 0 Y2 Z 0 Y2 Y1 3 Z 0 2 Z1 2 In the same way, S21 is: 0 1 Z1 S21 j 0 1 Z 0 Fig.1. FET T/R switch reference architecture. Terminating the switch ports (P1, P2 and P3) with Z0 (normalizing impedance, typically 50 Ohm) the network S-parameter description can be derived, resulting in: S11 Z0 ( Z1Y2 1) [1] 2 Z0 Y2 Z0 Y2 Y1 3 Z0 2 Z1 2 in which Y1 = 1/Z1, and S22 Z0 ( Z1Y2 1) 2 Z1 [2] 2 2 Z0 Y2 Z0 Y2 Y1 3 Z0 2 Z1 S33 Z0 ( Z1 2 Z 0 Z 2 ) [3] 3 Z0 Z 2 2 Z 2 Z1 2 Z0 2 Z0 Z1 j Z0 1 1 Y Y 0 2 [5] 0 1 0 j 2 Z 0 (1 Y2 Z 0 ) 2 Z 0 2 Y2 Z 0 Y2 Y1 3 Z 0 2 Z1 and S32: 0 j Z0 1 Z1 1 0 S32 j Y2 1 0 0 1 Z 0 j 2 Z0 2 2 Z 0 Y2 Z 0 Y2 Y1 3 Z 0 2 Z1 [6] By reciprocity, the complete S-matrix can be filled. Impedance Z1 in the previous expressions may or may not include L1: such series inductance can be used in some cases to compensate the effects of the FET parasitic capacitance at high frequencies; on the other hand, L2 is used to resonate the COFF of the second FET, so its value is fixed to IJMOT-2014-1-541 © 2014 IAMOT 80 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.9, NO.1, JANUARY 2014 L2 = 1/(COFF2∙ω02), ω0 being the central angular frequency. Derived expressions are independent on the particular model used to represent FETs in its ON and OFF states. To gather Z1 and Y2, a simplified FET model can be used for X-Band applications. In fact, a FET operating in its ohmic region can be modeled by a RON resistor only; in the other condition (pinch-off), it can be simply modeled by a COFF capacitor, as shown in Fig.3 (a). Parameters RON and COFF can be simply extracted by means of a very simple test circuit such as the one in Fig.3 (b). and the whole S-matrix is expressed as a function of RON1 and RON2, by which the FETs peripheries can be easily sized, for instance by means of design charts such as the ones depicted in Figs.45. For brevity, transmission parameters between ports 1-2, 1-3 (Fig.4-5) only are here shown (at 9.6 GHz). Using the so-obtained parameters RON and COFF allows to specify the previously derived equations. In particular, since the control voltage is unique, two cases need to be considered, namely with both FETs simultaneously ON or OFF. Fig.4. S21 design chart for FETs ON (top) and OFF (bottom) states. Fig.3. (a) Simplified FET’s model. (b) Reference circuit for RON and COFF extraction. Hence, all expressions computed above become functions of RON1, COFF1 and RON2, considering that COFF2 is resonated by L2. Finally, it is to note that the mathematical analysis can be further simplified by introducing two technology-dependent parameters, namely rON and cOFF, such that RON = rON/P and COFF = cOFF∙P, where P is the device periphery (N∙W). This yields: COFF cOFF rON RON [7] IJMOT-2014-1-541 © 2014 IAMOT 81 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.9, NO.1, JANUARY 2014 Fig.6. Layout of the demonstrator switch. Fig.5. S31 design chart for FETs ON (top) and OFF (bottom) states. III. FULL X-BAND DEMONSTRATOR To design a full X-Band demonstrator, OMMIC’s D01MH process has been selected, providing depletion metamorphic HEMTs with 0.13 µm gate length. For this technology, rON = 1.04 Ω∙mm and cOFF = 450 pF/mm. The resulting performance is plotted in Fig.7. Port match in non-reflective operation is 15 dB over the whole X-Band (8-12 GHz). Insertion losses are 0.7 dB and 1.6 dB in the branch 1-3 and 1-2, respectively. This suggests that path 1-3 be chosen for the RX mode; in such case, a better isolation is also obtained in TX mode between ports 2 and 3, namely 21.5 dB at 9.6 GHz, and over 20.5 dB over the whole X-Band. These results well agree at center frequency with the behavior predicted by the simplified analysis in Section II. By considering all the design charts, RON1 = 10 Ω and RON2 = 3 Ω were chosen, from which the FET peripheries can be determined (P = rON/RON). The final switch layout, with size 1 1 mm2, is depicted in Fig.6. A semi-lumped quarter-wave line has been used to reduce the circuit insertion loss. IJMOT-2014-1-541 © 2014 IAMOT 82 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.9, NO.1, JANUARY 2014 Fig. 7. Switch performance. [10] substrate”, Electronics Letters, Vol 46: pp. 16271629, Nov. 2010. R. Cory, D. Fryklund, “Solid State RF/Microwave Switch Technology: Part 2” MPD Microwave Product Digest, pp. 34-66, Jun. 2009. IV. CONCLUSIONS A design method for single control-voltage, compact, asymmetric switches has been proposed. A step-by-step procedure was outlined guiding the designer to obtain the best performance that a certain process technology can provide. A compact SPDT switch has been designed to demonstrate the methodology here discussed, exhibiting performance in close agreement with the theoretical analysis. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] W.V. McLevige, V. Sokolov “Microwave switching with parallel-resonated GaAs FETS”, IEEE Electron Device Letters, pp. 156-158, Aug. 1980. W. Ciccognani, M. Ferrari, E. Limiti, “Highisolation microstrip GaN HEMT single-fet switch”, International Journal on RF and Microwave Computer-Aided Engineering, Vol. 20, no. 4, pp. 391-398, 2010. V. Alleva, A. Bettidi, W. Ciccognani, M. De Dominicis, M. Ferrari, C. Lanzieri, E. Limiti, M. Peroni, “High-power monolithic AlGaN/GaN high electron mobility transistor switches”, International Journal of Microwave and Wireless Technologies, Vol. 1, Special Issue 04, pp. 339-345, 2009. A. Bentini, S. Colangeli, M. Ferrari, E. Limiti, “Broadband resistive-inductive compensated GaN-HEMT single-fet switch”, EuMC European Microwave Conference, pp. 1206-1209, 2010. W.V. McLevige, V. Sokolov “Resonated GaAs FET devices for microwave switching,” IEEE Transactions on Electon Devices, Vol 28, pp. 198204, Feb. 1981. A. Gopinath, J.B. Rankin “GaAs FET RF switches” IEEE Transactions on Electron Devices,: Vol 32 pp. 1272-1278, Jul. 1985. Y. Ayasli, R. Mozzi, L. Hanes, D. Reynolds, “An Xband 10 W monolithic transmit-receive GaAs FET switch” Microwave and Millimeter-Wave Monolithic Circuits Symposium, Vol 82, pp.42-46, Jun. 1982. K. Jang, J. Lee, S. Kim, K. Seo, “Compact RF Switch ICs Using Dielectric Overhang Gate Process and Stacked Inductor” Japanese Journal of Applied Physics, Vol 45, pp. 3401-3404, 2006. S.K. Yeo, Y.S. Kwon, “X-band high-power HEMT SPDT switch with selectively anodised aluminium IJMOT-2014-1-541 © 2014 IAMOT