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JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.17, NO.4, AUGUST, 2017 ISSN(Print) 1598-1657 https://doi.org/10.5573/JSTS.2017.17.4.499 ISSN(Online) 2233-4866
Manuscript received Oct. 25, 2016; accepted Jun. 29, 2017 1 Dept. of Information, Communication & Electronics Engineering, The Catholic University of Korea, Gyeonggi-do 14662, Korea 2 Dept. of Electrical Engineering, also with PNU-LG Smart Control Center, Pusan National University, Busan 609-735, Korea 3 Division of Electronics Engineering, Chonbuk National University, Jollabuk-do 561-756, Korea E-mail : [email protected]
A UHF CMOS Variable Gain LNA with Wideband Input Impedance Matching and GSM Interoperability
Doo Hyung Woo1, Ilku Nam2, Ockgoo Lee2, and Donggu Im3
Abstract—A UHF CMOS variable gain low-noise amplifier (LNA) is designed for mobile digital TV tuners. The proposed LNA adopts a feedback topology to cover a wide frequency range from 474 to 868 MHz, and it supports the notch filter function for the interoperability with the GSM terminal. In order to handle harmonic distortion by strong interferers, the gain of 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 of greater than 16 dB, NF of less than 1.7 dB, and IIP3 of greater than -1.7 dBm for the UHF band. Index Terms—CMOS, DVB-H/T, feedback, GSM interoperability (IOP), LNA, mobile TV tuner, variable gain
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 for Mobile Communications) chips in mobile terminals, as shown in Fig. 1. In the case of stand-alone usage, the
DVB-H/T tuner has to cover the UHF band from 474 to 868 MHz. When the DVB-H/T receiver operates with the GSM transceiver in mobile terminals, the upper limit of the input frequency is reduced to 746 MHz for GSM interoperability.
In order to support both stand-alone mode and interoperation mode with the GSM transceiver, the LNA should cover a wide frequency range from 474 to 868 MHz while having high out-of-band linearity to handle strong blockers without desensitization. There are two LNA design approaches for the DVB-H/T receiver,
(a)
(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.
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 of 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 frequency range. This narrowband impedance matching is able to attenuate the strong transmitter (Tx) blockers of GSM 850 (824~949 MHz) and GSM 900 (890~915 MHz) through the transmission loss by reflection and helps to support for GSM IOP. However, it is difficult to make constant gain, input impedance matching, and accurate gain step over a wide frequency range. In addition, the additional tuning circuit is required for compensating process, voltage, and temperature (PVT) variations.
In this paper, a feedback variable gain CMOS LNA with the notch filter function is proposed for DVB-H/T receiver with GSM IOP. Based on a single hardware, it supports both stand-alone mode with the operating frequency range from 474 to 868 MHz and TV-GSM interoperation mode with the operating frequency range from 474 to 746 MHz through the programmability. In addition, the gain of the proposed LNA is step-controlled while maintaining the input return loss (S11) of less than -10 dB. Section II presents the circuit design of the proposed LNA. Section III reports the results of experiments on the designed LNA, and conclusions are given in Section IV.
II. CIRCUIT DESIGN
Fig. 2 shows the GSM interference environment in the TV-GSM interoperation mode. Assuming the maximum output power of GSM Tx signal is about +33 dBm and the isolation between two antennas of the cellular and DVB-H/T is around 15 dB, GSM Tx signal with a power of +18 dBm can be coupled to the antenna of DVB-H/T receiver. Because this strong Tx leakage signal desensitizes the receiver and directly degrades the receiver sensitivity, the band rejection filter in front of the receiver is inevitably required to attenuate the Tx leakage signal. The out-of-band rejection characteristic of the commercial band rejection filter allows the incoming Tx leakage signal to be attenuated by 40 dB and as a result, the power of the leakage signal is reduced to about -22 dBm. However, unfortunately, the residue of
the Tx leakage signal can still desensitize the receiver if the linearity of the front-end is not sufficiently high. If there is no additional rejection of the Tx leakage signal, during the automatic gain control (AGC) operation, the gain setting of the LNA is changed to the low gain mode even though the desired signal is very weak. This results in the degradation of the receiver sensitivity. According to MBRAI 2.0 specifications [1], the sensitivity degradation should be less than 1.5 dB when the GSM Tx interferer is present. Therefore, the additional Tx blocker filtering should be supported by the LNA.
Fig. 3(a) shows the proposed resistive shunt feedback LNA with a second-order notch filter. Basically, it provides a wideband input impedance matching characteristic over the UHF band. The second-order LC notch filter is designed by the combination of two first-order LC filters placed at the input and output of the LNA. It adopts two external inductors L1 and L2 and on-chip digitally controlled switched capacitor array to keep high quality factor (Q-factor) of the filter and achieve large attenuation of the GSM Tx leakage signal. The input and output LC filter attenuates the GSM Tx leakage signal through the transmission loss by reflection and gain reduction by load impedance control, respectively. When the on-chip switched capacitor array is in fully off-state, the band-stop frequency of the notch filter moves out of the operating frequency and the LNA covers the entire UHF band from 474 to 868 MHz.
Fig. 3(b) shows the simplified small-signal equivalent circuit of the proposed LNA with a second-order notch filter. The transfer function of the proposed LNA is given as
GSM Tx signalGSM850 : 824 ~ 849 MHzGSM900 : 890 ~ 915 MHz
Frequency
GSM Transmitter
DVB-H/TReceiver
Frequency
33 dBm
18 dBm Tx signal coupling
Isolation (~ 15 dB)DVB-H/T signal
(474 – 746 MHz)
GSM rejection filter
RF filter
Fig. 2. GSM interference environment in the TV-GSM interoperation mode.
JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.17, NO.4, AUGUST, 2017 501
{ }
{ }
1
2
1/ ( )( )
( )
( ( ) ) || ( ) ||1 / || ( )
( )( ) || || || || ( ) || ( ) || ,
1 / ( )
m foutV
in s m
m s gs f
ff o L L L
m f
G Z sVA s
V R Z s
Z s R Z s sC Z s
Z sZ s R sL R Z s Z s
G Z s
-= » - ´
+
é +ëùæ ö
´ úç ÷ç ÷- úè øû
(1)
where Rs is the source impedance, Gm (» gm1) is the short circuit transconductance of the cascode amplifier, Zm(s) is the impedance of the input matching network, Z1(s) is the impedance of the input notch filter, Zf(s) is the impedance of the feedback network, Ro (» ro1 + ro2 + gm2ro1ro2) is the output impedance of the cascode amplifier, Z2(s) is the impedance of the output notch filter, and ZL(s) is the input impedance of the following circuit of the down-conversion mixer.
In case of the input impedance of the proposed LNA, it is calculated as following:
2
2
( ) || || ( ) || ( )( )
1 ( || || ( ) || ( ))f L L L
im L L L
Z s sL R Z s Z sZ s
G sL R Z s Z s+
»+
. (2)
Most of the conventional feedback LNAs have implemented the variable gain function by controlling only Zf(s). However, from (2), this causes the variation of the input impedance and S11. In order to achieve a small variation of S11 over wide gain control range, both feedback resistor Rf and load resistor RL 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 of the proposed LNA is shown in Fig. 4. The chip size is about 550 µm ´ 450 µm. The current consumption of the designed LNA is 6 mA at a 1.5 V supply voltage.
Fig. 5 shows the measured input return loss (S11) of the proposed LNA when the LC notch filter is turned on and off, respectively. As predicted, when the LC notch filter is turned off, the LNA covers the entire UHF band from 474 to 868 MHz. As shown in Fig. 5, when the LC notch filter is enabled, the input impedance of the LNA is unmatched to the source impedance at GSM frequency band and this relaxes the linearity requirement of the front-end due to the additional rejection of GSM Tx
Input
Bias
Zm(s)
LLL2
C2
Rf
Cf
L1
VLG,cont
VLG,cont C3
R2 R3
Output
Low gain path
C4
R4
R1C1
- C3, C4, Cf : 6 pF- C5, C8 : 1 pF- R1, R4 : 14 kW- Rf : 600 W, R2 : 10 W, R3 : 210 W
M1
M2
M3
M4
- M1, M2 : 800u/0.11u,- M3: 25u/0.11u, M4: 40u/0.11u- LL : 15nH- L1, L2 : 51nH
(a)
(b)
Fig. 3. (a) Schematic of the proposed feedback variable gain LNA with notch filter function, (b) its simplified small-signal equivalent circuit without the low gain path. The L1, L2, and LLare external components.
Fig. 4. Chip photograph of the proposed LNA.
Fig. 5. Measured input return loss (S11) of the proposed LNA when LC notch filter is turned on and off, respectively.
502 DOO HYUNG WOO et al : A UHF CMOS VARIABLE GAIN LNA WITH WIDEBAND INPUT IMPEDANCE MATCHING AND …
signal. And as a result, the upper limit of the input frequency is reduced to 746 MHz.
Fig. 6 show the measured gain of the proposed LNA over various gain modes when the LC notch filter is turned off. The designed LNA covers a 20 dB gain range with a 10 dB gain step. Fig. 7 shows the measured gain of the LNA at high gain mode when the LC notch filter is activated.
As shown in Fig. 8, S11 of the LNA is less than -10 dB for all gain modes. It shows a small variation of S11 over the wide gain control range because both feedback and load resistance values are changed simultaneously according to the gain modes. Fig. 9 shows the measured NF and third-order input-referred intercept point (IIP3) of the proposed LNA at high gain mode when the LC notch filter is turned off. The NF and IIP3 of the designed LNA are less than 1.7 dB and greater than -1.7 dBm over the entire UHF band, respectively.
IV. CONCLUSIONS
A UHF CMOS feedback variable gain LNA with wideband input impedance matching and GSM interoperability (IOP) is proposed for DVB-H/T receivers. Based on a single hardware, it supports both stand-alone mode with the operating frequency range from 474 to 868 MHz and TV-GSM interoperation mode with the operating frequency range from 474 to 746 MHz
Fig. 6. Measured gain of the proposed LNA over various gain modes when LC notch filter is turned off.
Fig. 7. Measured gain of the proposed LNA at high gain mode when LC notch filter is turned on.
Fig. 8. Measured input return loss (S11) of the proposed LNA over various gain modes when the LC notch filter is turned off.
400 500 600 700 800 9001.00
1.25
1.50
1.75
2.00
NF
(dB)
Frequency (MHz)
(a)
400 500 600 700 800 900-3
-2
-1
0
1
2
IIP3 (
dBm
)
Frequency (MHz)
(b)
Fig. 9. (a) Measured NF, (b) third-order input-referred intercept point (IIP3) of the proposed LNA at high gain mode when the LC notch filter is turned off.
JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.17, NO.4, AUGUST, 2017 503
through the programmability. In the TV-GSM interoperation mode, the second-order notch filter embedded in the LNA attenuates the GSM Tx leakage signal through the transmission loss by reflection and gain reduction by load impedance control. It relaxes the linearity requirement of the front-end.
ACKNOWLEDGEMENT
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2015R1C1A1A02037679).
REFERENCES
[1] Mobile and Portable DVB-T/H Radio Access–Part 1: Interface Specification, EICTA, 2007..
[2] I. Nam, C. Choi, O. Lee, and H. Moon, “A fully differential RC calibrator for accurate cut-off frequency of a programmble channel selection filter,” J. of Semiconductor Technology and Science, vol. 16, no. 5, pp. 1–5, Oct. 2016.
[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. of Solid-State Circuits, vol. 44, no. 3, pp. 740-750, Mar. 2009.
[4] I. Nam, et al., “A wideband CMOS RF front-end using ac-coupled current mirrored technique for multiband multistandard mobile TV tuners,” IEEE Microwave and Wireless Component Lett., vol. 17, no 10, pp. 739-741, Oct. 2007.
[5] D. Im and I. Nam, “A widebnad digital TV receiver front-end with noise and distrotion cancellation,” IEEE Trans. Circuits Syst. I: Regular Papars, vol. 61, no. 2, pp. 562-572, Feb. 2014.
[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 for mobile TV SoC with GSM interoperability,” IEEE Radio Integrated Circuits Symposium, Aneheim, CA, pp. 189-192, May 2010.
[7] I. Nam, Y.-J. Kim, and H.-W. Moon, “Feedback-type variable gain amplifier and method of controllong the same”, US patent 7,633,337, Dec. 15, 2009.
Doo Hyung Woo received the B.S. degree from the Department of Electronics Engineering of Yonsei University in 1999 and the M.S. degree and Ph.D. from the Depart- ment of Electrical Engineering and Computer Science of the Korea
Advanced Institute of Science and Technology (KAIST) in 2001 and 2005, respectively. His main research interest was mixed signal circuit designs for infrared detectors while a Ph.D. candidate. He joined the LCD Business of Samsung Electronics Co. in 2005 as a Senior Engineer. Currently, he is an associate professor at the Catholic University of Korea.
Ilku Nam received the B.S. degree in EE from Yonsei University, Korea, in 1999, and the M.S. and Ph.D. degrees in EECS from 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 of mobile digital TV tuner IC. In 2007, he joined the School of Electrical Engineering, Pusan National University, Busan, Korea, and is now a Professor.
Ockgoo Lee received the B.S. degree in electrical engineering from Sungkyunkwan University, Korea, in 2001, the M.S. degree in electrical engineering from the KAIST, Korea, in 2005, and the Ph.D. degree in electrical and computer engineering
from the Georgia Institute of Technology, USA, in 2009. Upon completion of the doctoral degree, he joined Qualcomm Inc., USA, as a Senior Engineer, where he was involved in the development of transmitters and integrated passive circuits on mobile applications. He is currently a faculty member with the Department of Electrical Engineering, Pusan National University, Korea. His research interests include high-frequency integrated circuits and system design for wireless communications and biomedical applications.
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 from the Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea, in 2004, 2006, and 2012, respectively. His doctoral
research focused on integrated RF front-ends with antenna switch, power amplifier, 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 of 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 of the first RF SOI CMOS technology in Korea with SOI business team in National NanoFab Center (NNFC), Daejeon, Korea, and was responsible for the design of antenna switch, digitally tunable capacitor, power MOSFETs, and ESD devices. In 2013, he joined the Texas Analog Center of Excellence (TxACE), Department of Electrical Engineering, University of 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 of Electronics Engineering, Chonbuk National University, Jeollabuk-do, Korea, and is now an Assistant Professor. His research interests are CMOS analog/RF/mm-wave ICs and system design for wireless communications.
