A UHF CMOS Variable Gain LNA with Wideband Input Impedance Matching and GSM Interoperability

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1 JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.17, NO.4, AUGUST, 2017 ISSN(Print) ISSN(Online) A UHF CMOS Variable Gain LNA with Wideband Input Impedance Matching and GSM Interoperability Doo Hyung Woo 1, Ilku Nam 2, Ockgoo Lee 2, and Donggu Im 3 Abstract A UHF CMOS variable gain low-noise ampliier (LNA) is designed or mobile digital TV tuners. The proposed LNA adopts a eedback topology to cover a wide requency range rom 474 to 868 MHz, and it supports the notch ilter unction or the interoperability with the GSM terminal. In order to handle harmonic distortion by strong intererers, the gain o the proposed LNA is step-controlled while keeping almost the same input impedance. The proposed LNA is implemented in a 0.11 mm CMOS process and consumes 6 ma at a 1.5 V supply voltage. In the measurement, it shows the power gain o greater than 16 db, NF o less than 1.7 db, and IIP3 o greater than -1.7 dbm or the UHF band. (a) Index Terms CMOS, DVB-H/T, eedback, GSM interoperability (IOP), LNA, mobile TV tuner, variable gain Manuscript received Oct. 25, 2016; accepted Jun. 29, Dept. o Inormation, Communication & Electronics Engineering, The Catholic University o Korea, Gyeonggi-do 14662, Korea 2 Dept. o Electrical Engineering, also with PNU-LG Smart Control Center, Pusan National University, Busan , Korea 3 Division o Electronics Engineering, Chonbuk National University, Jollabuk-do , Korea dgim@jbnu.ac.kr I. INTRODUCTION DVB-H/T (Digital Video Broadcasting-Handheld/ Terrestrial) is the mobile TV standard in Europe [1-4]. DVB-H/T tuners have been used independently in mobile electronic devices or with GSM (Global System or Mobile Communications) chips in mobile terminals, as shown in Fig. 1. In the case o stand-alone usage, the (b) Fig. 1. (a) Stand-alone DVB-H/T tuner in mobile electronic devices, (b) DVB-H/T tuner with GSM transceiver in mobile terminals. DVB-H/T tuner has to cover the UHF band rom 474 to 868 MHz. When the DVB-H/T receiver operates with the GSM transceiver in mobile terminals, the upper limit o the input requency is reduced to 746 MHz or GSM interoperability. In order to support both stand-alone mode and interoperation mode with the GSM transceiver, the LNA should cover a wide requency range rom 474 to 868 MHz while having high out-o-band linearity to handle strong blockers without desensitization. There are two LNA design approaches or the DVB-H/T receiver,

2 500 DOO HYUNG WOO et al : A UHF CMOS VARIABLE GAIN LNA WITH WIDEBAND INPUT IMPEDANCE MATCHING AND including the multiple tuned narrowband LNAs and the wideband LNAs [5, 6]. In case o the multiple tuned narrowband LNAs, the tunable capacitors, such as varactor diodes and switched capacitor array, are inevitably employed to tune the narrowband input impedance matching over a wide requency range. This narrowband impedance matching is able to attenuate the strong transmitter (Tx) blockers o GSM 850 (824~949 MHz) and GSM 900 (890~915 MHz) through the transmission loss by relection and helps to support or GSM IOP. However, it is diicult to make constant gain, input impedance matching, and accurate gain step over a wide requency range. In addition, the additional tuning circuit is required or compensating process, voltage, and temperature (PVT) variations. In this paper, a eedback variable gain CMOS LNA with the notch ilter unction is proposed or DVB-H/T receiver with GSM IOP. Based on a single hardware, it supports both stand-alone mode with the operating requency range rom 474 to 868 MHz and TV-GSM interoperation mode with the operating requency range rom 474 to 746 MHz through the programmability. In addition, the gain o the proposed LNA is step-controlled while maintaining the input return loss (S 11 ) o less than - 10 db. Section II presents the circuit design o the proposed LNA. Section III reports the results o experiments on the designed LNA, and conclusions are given in Section IV. II. CIRCUIT DESIGN Fig. 2 shows the GSM intererence environment in the TV-GSM interoperation mode. Assuming the maximum output power o GSM Tx signal is about +33 dbm and the isolation between two antennas o the cellular and DVB-H/T is around 15 db, GSM Tx signal with a power o +18 dbm can be coupled to the antenna o DVB-H/T receiver. Because this strong Tx leakage signal desensitizes the receiver and directly degrades the receiver sensitivity, the band rejection ilter in ront o the receiver is inevitably required to attenuate the Tx leakage signal. The out-o-band rejection characteristic o the commercial band rejection ilter allows the incoming Tx leakage signal to be attenuated by 40 db and as a result, the power o the leakage signal is reduced to about -22 dbm. However, unortunately, the residue o 33 dbm GSM Tx signal GSM850 : 824 ~ 849 MHz GSM900 : 890 ~ 915 MHz Frequency 18 dbm Tx signal coupling DVB-H/T signal ( MHz) Frequency RF ilter Isolation (~ 15 db) GSM rejection ilter GSM Transmitter DVB-H/T Receiver Fig. 2. GSM intererence environment in the TV-GSM interoperation mode. the Tx leakage signal can still desensitize the receiver i the linearity o the ront-end is not suiciently high. I there is no additional rejection o the Tx leakage signal, during the automatic gain control (AGC) operation, the gain setting o the LNA is changed to the low gain mode even though the desired signal is very weak. This results in the degradation o the receiver sensitivity. According to MBRAI 2.0 speciications [1], the sensitivity degradation should be less than 1.5 db when the GSM Tx intererer is present. Thereore, the additional Tx blocker iltering should be supported by the LNA. Fig. 3(a) shows the proposed resistive shunt eedback LNA with a second-order notch ilter. Basically, it provides a wideband input impedance matching characteristic over the UHF band. The second-order LC notch ilter is designed by the combination o two irstorder LC ilters placed at the input and output o the LNA. It adopts two external inductors L 1 and L 2 and onchip digitally controlled switched capacitor array to keep high quality actor (Q-actor) o the ilter and achieve large attenuation o the GSM Tx leakage signal. The input and output LC ilter attenuates the GSM Tx leakage signal through the transmission loss by relection and gain reduction by load impedance control, respectively. When the on-chip switched capacitor array is in ully ostate, the band-stop requency o the notch ilter moves out o the operating requency and the LNA covers the entire UHF band rom 474 to 868 MHz. Fig. 3(b) shows the simpliied small-signal equivalent circuit o the proposed LNA with a second-order notch ilter. The transer unction o the proposed LNA is given as

3 JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.17, NO.4, AUGUST, R 4 L L L 2 C 2 Output Input Z m (s) C R L 1 C 1 Bias C 4 M 1 R 1 - M 1, M 2 : 800u/0.11u, - M 3 : 25u/0.11u, M 4 : 40u/0.11u - L L : 15nH - L 1, L 2 : 51nH M 2 V LG,cont C3 R 2 R 3 V LG,cont Low gain path - C 3, C 4, C : 6 pf - C 5, C 8 : 1 pf - R 1, R 4 : 14 kw - R : 600 W, R 2 : 10 W, R 3 : 210 W (a) M 3 M 4 Fig. 4. Chip photograph o the proposed LNA. V Gm -1/ Z out AV =» - V R + Z in s m {( Zm Rs ) Z1 1/ scgs Z } é ë + æ Z öù { Z Ro sll RL Z2 Z L } ú, ç Gm -1/ Z è øûú (1) where R s is the source impedance, G m (» g m1 ) is the short circuit transconductance o the cascode ampliier, Z m (s) is the impedance o the input matching network, Z 1 (s) is the impedance o the input notch ilter, Z (s) is the impedance o the eedback network, R o (» r o1 + r o2 + g m2 r o1 r o2 ) is the output impedance o the cascode ampliier, Z 2 (s) is the impedance o the output notch ilter, and Z L (s) is the input impedance o the ollowing circuit o the down-conversion mixer. In case o the input impedance o the proposed LNA, it is calculated as ollowing: Z i (b) Fig. 3. (a) Schematic o the proposed eedback variable gain LNA with notch ilter unction, (b) its simpliied small-signal equivalent circuit without the low gain path. The L 1, L 2, and L L are external components. Z + sl R Z Z L L 2 L». (2) + 1 G ( sl R Z Z ) m L L 2 L Fig. 5. Measured input return loss (S 11 ) o the proposed LNA when LC notch ilter is turned on and o, respectively. Most o the conventional eedback LNAs have implemented the variable gain unction by controlling only Z (s). However, rom (2), this causes the variation o the input impedance and S 11. In order to achieve a small variation o S 11 over wide gain control range, both eedback resistor R and load resistor R L are changed simultaneously in the proposed LNA [7]. III. EXPERIMENTAL RESULTS The proposed LNA was implemented in a 0.11-μm CMOS process. The chip photograph o the proposed LNA is shown in Fig. 4. The chip size is about 550 µm 450 µm. The current consumption o the designed LNA is 6 ma at a 1.5 V supply voltage. Fig. 5 shows the measured input return loss (S 11 ) o the proposed LNA when the LC notch ilter is turned on and o, respectively. As predicted, when the LC notch ilter is turned o, the LNA covers the entire UHF band rom 474 to 868 MHz. As shown in Fig. 5, when the LC notch ilter is enabled, the input impedance o the LNA is unmatched to the source impedance at GSM requency band and this relaxes the linearity requirement o the ront-end due to the additional rejection o GSM Tx

4 502 DOO HYUNG WOO et al : A UHF CMOS VARIABLE GAIN LNA WITH WIDEBAND INPUT IMPEDANCE MATCHING AND Fig. 6. Measured gain o the proposed LNA over various gain modes when LC notch ilter is turned o. Fig. 8. Measured input return loss (S11) o the proposed LNA over various gain modes when the LC notch ilter is turned o NF (db) Frequency (MHz) (a) 2 Fig. 7. Measured gain o the proposed LNA at high gain mode when LC notch ilter is turned on. IIP3 (dbm) signal. And as a result, the upper limit o the input requency is reduced to 746 MHz. Fig. 6 show the measured gain o the proposed LNA over various gain modes when the LC notch ilter is turned o. The designed LNA covers a 20 db gain range with a 10 db gain step. Fig. 7 shows the measured gain o the LNA at high gain mode when the LC notch ilter is activated. As shown in Fig. 8, S11 o the LNA is less than -10 db or all gain modes. It shows a small variation o S11 over the wide gain control range because both eedback and load resistance values are changed simultaneously according to the gain modes. Fig. 9 shows the measured NF and third-order input-reerred intercept point (IIP3) o the proposed LNA at high gain mode when the LC notch ilter is turned o. The NF and IIP3 o the designed LNA are less than 1.7 db and greater than -1.7 dbm over the entire UHF band, respectively Frequency (MHz) (b) Fig. 9. (a) Measured NF, (b) third-order input-reerred intercept point (IIP3) o the proposed LNA at high gain mode when the LC notch ilter is turned o. IV. CONCLUSIONS A UHF CMOS eedback variable gain LNA with wideband input impedance matching and GSM interoperability (IOP) is proposed or DVB-H/T receivers. Based on a single hardware, it supports both stand-alone mode with the operating requency range rom 474 to 868 MHz and TV-GSM interoperation mode with the operating requency range rom 474 to 746 MHz

5 JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.17, NO.4, AUGUST, through the programmability. In the TV-GSM interoperation mode, the second-order notch ilter embedded in the LNA attenuates the GSM Tx leakage signal through the transmission loss by relection and gain reduction by load impedance control. It relaxes the linearity requirement o the ront-end. ACKNOWLEDGEMENT This research was supported by Basic Science Research Program through the National Research Foundation o Korea (NRF) unded by the Ministry o Education (NRF-2015R1C1A1A ). REFERENCES [1] Mobile and Portable DVB-T/H Radio Access Part 1: Interace Speciication, EICTA, [2] I. Nam, C. Choi, O. Lee, and H. Moon, A ully dierential RC calibrator or accurate cut-o requency o a programmble channel selection ilter, J. o Semiconductor Technology and Science, vol. 16, no. 5, pp. 1 5, Oct [3] M.-C. Kuo, et al., A 1.2 V 114 mw dual-band direct-conversion DVB-H tuner in 0.13 mm CMOS, IEEE J. o Solid-State Circuits, vol. 44, no. 3, pp , Mar [4] I. Nam, et al., A wideband CMOS RF ront-end using ac-coupled current mirrored technique or multiband multistandard mobile TV tuners, IEEE Microwave and Wireless Component Lett., vol. 17, no 10, pp , Oct [5] D. Im and I. Nam, A widebnad digital TV receiver ront-end with noise and distrotion cancellation, IEEE Trans. Circuits Syst. I: Regular Papars, vol. 61, no. 2, pp , Feb [6] H. Kim, S. Kang, J.-H. Chang, J.-H. Choi, H. Chung, J. Heo, J.-D. Bae, W. Choo, and B.-H. Park, A multi-standard multi-band tuner or mobile TV SoC with GSM interoperability, IEEE Radio Integrated Circuits Symposium, Aneheim, CA, pp , May [7] I. Nam, Y.-J. Kim, and H.-W. Moon, Feedbacktype variable gain ampliier and method o controllong the same, US patent 7,633,337, Dec. 15, Doo Hyung Woo received the B.S. degree rom the Department o Electronics Engineering o Yonsei University in 1999 and the M.S. degree and Ph.D. rom the Department o Electrical Engineering and Computer Science o the Korea Advanced Institute o Science and Technology (KAIST) in 2001 and 2005, respectively. His main research interest was mixed signal circuit designs or inrared detectors while a Ph.D. candidate. He joined the LCD Business o Samsung Electronics Co. in 2005 as a Senior Engineer. Currently, he is an associate proessor at the Catholic University o Korea. Ilku Nam received the B.S. degree in EE rom Yonsei University, Korea, in 1999, and the M.S. and Ph.D. degrees in EECS rom the KAIST, Korea, in 2001 and 2005, respectively. From 2005 to 2007, he was a Senior Engineer with Samsung Electronics, Gyeonggi, Korea, where he was involved in the development o mobile digital TV tuner IC. In 2007, he joined the School o Electrical Engineering, Pusan National University, Busan, Korea, and is now a Proessor. Ockgoo Lee received the B.S. degree in electrical engineering rom Sungkyunkwan University, Korea, in 2001, the M.S. degree in electrical engineering rom the KAIST, Korea, in 2005, and the Ph.D. degree in electrical and computer engineering rom the Georgia Institute o Technology, USA, in Upon completion o the doctoral degree, he joined Qualcomm Inc., USA, as a Senior Engineer, where he was involved in the development o transmitters and integrated passive circuits on mobile applications. He is currently a aculty member with the Department o Electrical Engineering, Pusan National University, Korea. His research interests include high-requency integrated circuits and system design or wireless communications and biomedical applications.

6 504 DOO HYUNG WOO et al : A UHF CMOS VARIABLE GAIN LNA WITH WIDEBAND INPUT IMPEDANCE MATCHING AND Donggu Im received the B.S., M.S., and Ph.D. degrees in electrical engineering and computer science rom the Korea Advanced Institute o Science and Technology (KAIST), Daejeon, Korea, in 2004, 2006, and 2012, respectively. His doctoral research ocused on integrated RF ront-ends with antenna switch, power ampliier, directional coupler with transmitter leakage suppression, and tunable impedance matching circuit in silicon-on-insulator (SOI) CMOS. From 2006 to 2009, he was an Associate Research Engineer with LG Electronics, Seoul, Korea, where he was involved in the development o universal analog and digital TV receiver ICs. From 2012 to 2013, he was a Post-Doctoral Researcher with KAIST, where he was involved in the development o the irst RF SOI CMOS technology in Korea with SOI business team in National NanoFab Center (NNFC), Daejeon, Korea, and was responsible or the design o antenna switch, digitally tunable capacitor, power MOSFETs, and ESD devices. In 2013, he joined the Texas Analog Center o Excellence (TxACE), Department o Electrical Engineering, University o Texas at Dallas, as a Research Associate, where he developed ultra-low-power CMOS radios with adaptive impedance tuning circuits. In 2014, he joined the Division o Electronics Engineering, Chonbuk National University, Jeollabuk-do, Korea, and is now an Assistant Proessor. His research interests are CMOS analog/rf/mm-wave ICs and system design or wireless communications.