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2 A Multi-band CMOS Low Noise Amplifier for Multi-standard Wireless eceivers Chyuen-Wei An,, Yuanjin Zhen, Chun-Huat Hen Institute of Microelectronics, Sinapore, National University of Sinapore, Sinapore Abstract A novel multi-band low noise amplifier (LNA) that allows simultaneous reception of sinals from several wireless standards is desined and implemented usin a.8-µm CMOS technoloy. The circuit topoloy consists of a 3-stae wideband LNA and notch filters. The desined LNA can provide concurrent three bands over.93~.8 GHz with measured ain (S) of ~4 db, input reflection ratio (S) of -3~-7 db, noise fiure (NF) of 4.4~4.78 db, and 3 rd order input intercept point (IIP3) of -.3~-.4dBm respectively. In addition, a minimum 8 db of interband ain suppression is achieved. This work has achieved a better fiure of merit (FOM) than other related works, in terms of ain, noise fiure and power consumption trade-offs. I. INTODUCTION ecent developments in wireless communication have resulted in many widely adopted wireless standards, with each caterin to different needs dependin on their data rates, operatin rane, bandwidth requirement and carrier frequency. Althouh multi-band transceivers have been introduced, they mainly focus on band switchin which forbid the concurrent operation of various standards []. It is desirable to provide true multi-band transceiver where various wireless standards can operate simultaneously to extend its functionalities []. One of the key buildin blocks for multi-band transceiver is the low noise amplifier (LNA). There are three ways of implementin a multi-band LNA. The simplest way is to use a separate LNA for each standard, resultin in larer die area, hiher cost and power. The second alternative is to desin a wideband LNA [3], [4]. Althouh it offers the benefits of smaller area and power, the sensitivity suffers severely with lare out-of-band unwanted blocker due to the non-linearity of the transistor. The last method is the concurrent dual-band LNA [] that offers better trade-off between area, power and sensitivity. In this paper, the idea of concurrent LNA is adopted and extended beyond dual-band. A new circuit topoloy suitable for the multi-band implementation over a wide frequency band is also proposed. The list of standards for the multi-band LNA in this work is shown in Table I. The standards are rouped into bands based on their carrier frequencies to determine the number of notches required and their correspondin inter-band notch frequencies. In Section II, the circuit of the multi-band LNA is first discussed, followed by analysis on the ain, noise and impedance matchin of the desin in Section III. The experimental results are reported in Section IV. The conclusion is iven in Section V. Frequency Band TABLE I FEQUENCY BANDS Wireless Standard II. CICUIT DESIGN Frequency Spectrum (MHz) GSM 93 ~ 96 DCS-8 8 ~ 8 DECT 88 ~ 897 PCS-9 93 ~ 96 WCDMA ~ 7 WLAN (8.b/) 4 ~ 483 Bluetooth (8.FH) 4 ~ WLAN (8.a) ~ 8 Notch filter can be embedded in a wideband LNA circuit to achieve multi-band operation [], [6]. The wideband LNA is employed to provide desired ain over a wide frequency spectrum. The notch filters are then used to achieve inter-band ain suppression to reject lare unwanted out-of-band blockers. The wideband LNA is desined to provide a relatively flat ain from.93~.8 GHz and the chosen topoloy is shown in Fi.. The LNA consists of three cascaded staes. The first two staes are common source amplifiers with shunt feedback throuh a source follower [3], whereas the last stae is an inductively deenerated common source amplifier with an input LC ladder network [4]. Each stae of the cascade serves a different purpose. The first stae with moderate ain is introduced to improve the overall system noise fiure without severely affectin the sensitivity. The notch filters are only embedded in the last two staes to remove the lare unwanted out-of-band blockers so that the noisy active Q enhancement circuit would not impact the overall noise fiure. The inductors and capacitors used for the resonant networks have been well characterized from previous fabrication. The overall ain is distributed amon the three staes after careful trade-off between the sensitivity and noise fiure requirement. For the first stae, low noise fiure and ood input impedance matchin can be achieved simultaneously as the optimization of the noise fiure and the impedance matchin are separately controlled by transistors M and M [3]. For the last stae, cascode transistor M 6 is employed to improve the reverse isolation. In addition, an embedded LC ladder network is placed at its input for band shapin purposes by havin steeper roll-off at both the lower and upper cut-off frequencies [4] /7 $. 7 IEEE. 8

3 Fi.. Schematic of multi-band multi-mode LNA (a wideband LNA with notch filters connected to nodes X and Y). The notch filter in Fi. is connected to node X in Fi.. It is used to create a notch at the frequency between the first bands []. At resonance (formed by C 7, L and varactor V ), the filter provides a low impedance path to round and thus reduces the sinal amplitude at the output of the second stae. This creates a notch in the ain. A sinle-ended PMOS Q enhancement circuit (M 8, M 9 and I s4 ) introduces neative resistance to cancel the on-chip resistive losses of L. The notch filter in Fi. 3 is connected to node Y in Fi. and forms a notch at the frequency between band and 3. The idea is similar to [6] but uses only one Q enhancement network. The series LC network is formed by C 8, L, C s of M, C, and varactors V and V 3. M provides the neative resistance needed to improve the quality factor of the on-chip inductor. boostin is employed to introduce an additional zero (s = - /L 9 ) to extend the bandwidth. L 9 also enerates an unwanted spurious resonance with C out, which has to be kept out-of-band [4]. Within III. CICUIT ANALYSIS Fi.. Schematic of notch filter connected to node X. A. Gain Analysis The ain of the first stae is shown as follows: ( sl G = + D )[ s ( ) ] m L C s + s m + m L C s m. () s C ( L + L ) + s( C + L ) + s The ain equation of the second stae can be obtained by replacin () with a different set of parameters. The inductor L introduced an additional zero (s = - D /L ) to help improve the amplifier bandwidth. It is worth notin that () reduces to the ain equation in [3] at low frequencies. The ain of the last stae is as follows [4]: s D m G sl + 9 m m 7 ext 3 = () scs W ( s) + sc out + s L9Cout + m 7 ext where W (s) is the impedance of the embedded LC ladder network, C out = C db6 +C d7 and ext = Ω. Similar inductor Fi. 3. Schematic of notch filter connected to node Y. 83

4 the network W (s), L 6 and C determine the lower cut-off frequency whereas L and C 6 determine the upper cut-off frequency [7]. B. Input Matchin The real part of the input impedance of the first stae amplifier is iven by: Z in = m m { G ω L[ C ( G ω [ C ) s s C C s s ( G )]}. (3) ( G )] At low frequencies, (3) reduces to the impedance shown in [3]. L and m are chosen to match the source resistance of Ω within the desired band without affectin the ain (G ) and noise. C. Noise Analysis As the first stae limits the overall achievable noise fiure, it is analyzed in detail as follows [3]: F = m D γ γ + 4m 4( ) S + m D m Is Sγ Is D S ( + m ) D where γ, γ, γ Is are the noise factors of M, M and M Is (where M Is is the transistor representin the current source I s ). Based on (4), the overall noise can be reduced by maximizin m, and minimizin mis. The chosen shunt feedback confiuration allows the separate optimization of noise performance and impedance matchin, throuh m and m respectively. The detailed noise analysis of the third stae can be found in [4]. Since its noise component is further suppressed by the ain of the first two staes, its noise performance can be trade-off with the desired ain, sensitivity and band shapin of the third stae. IV. MEASUEMENT ESULTS The proposed circuit was implemented usin Chartered s.8-µm CMOS technoloy and it operates under a.8-v supply. The simulated and measured ain (S) and input reflection coefficient (S) of the LNA are shown in Fi. 4. The measured ain in band (93~96 MHz), band (.8~.483 GHz), and band 3 (.~.8 GHz) are 7~9 db, 6~4 db, and ~3 db respectively. The measured and the simulated S for band aree well with each other. As for band and band 3, the measured S is 4 db less than the simulated fiure. This may be due to the discrepancy between the predicted and the actual quality factor of the inductors at these frequency bands, which reduces the overall achievable ain. A minimum 8 db of inter-band ain suppression is obtained. The lower inter-band ain suppression is due to the low Q factor of the active notch filters. S values of -3~-7 db, coverin frequencies from 9 MHz to 6 GHz, are achieved and it matches well with the simulation. The measured noise fiure shown in Fi. is about 4.4~4.78 db within the bands and is about db hiher than the simulated fiure. The lower LNA (4) 84 Fi. 4. Measured and simulated ain (S) and input reflection coefficient (S). Noise Fiure [db] Measured Simulated Frequency [GHz] Fi.. Measured and simulated noise fiure. ain obtained and the inductor Q factor could be responsible for this increase in the measured noise fiure. The resultin thirdorder input intercept point (IIP3) and -db compression point usin two tone test (94 and 9 MHz) are shown in Fi. 6. The IIP3 of -.8 dbm and -db compression point of -3.7 dbm are obtained. The die photo, shown in Fi. 7, occupied.7. mm (excludin pads). The performance parameters for different carrier frequencies and its comparison with other works are summarized in Table II. Our desin has achieved much hiher ain than the other desins at the cost of hiher power. The amplifier stae has been over-desined for hih ain with lare transconductance (hih current) in this work. The current can be further reduced by either usin a larer output resistance or a larer transistor sizin to keep the same ain. For fair comparison, a fiure of merit (FOM) introduced in [8] is adopted and the calculated value is also tabulated in Table II: S FOM =. () ( NF ) Power[ mw ] Based on the calculated FOM, our LNA performs better than all other related works for the two hiher frequency bands (> GHz) except for []. For band (< GHz), our work also out performs [3], the only other amplifier that covers the similar band in the comparison. It should be pointed out that althouh [] achieves the best performance due to its narrow band tune amplifier architecture, the architecture is not easily extendable to multi-band operation over a wider frequency spectrum. On the

5 4 Output Power Input Power Fi. 6. Measured two-tone test at 94 MHz (Band ). Fi. 7. Die Photo other hand, our LNA can provide out-of-band unwanted blocker suppression for improved sensitivity compared to the simple wideband architecture in [3] and [4]. The lower IIP3 performance is due to the hiher achievable ain of the LNA, which has been over-desined. Thus, IIP3 can be improved on by reducin the ain. The.3-µm technoloy employed by [], which allows hiher operatin voltae, also results in better linearity performance, while [3] has achieved better linearity at the expense of hih power consumption. Also, [] has achieved a better noise fiure due to the use of the common source with inductor deeneration confiuration. However, it is only suitable for narrowband desins. The proposed method in this paper can be easily extended to create more bands V. CONCLUSION A multi-band multi-mode LNA suitable for concurrent application has been proposed. It employs a 3-stae wideband LNA with notch filters. The concept has been successfully demonstrated over three bands coverin a wide frequency spectrum for various wireless standards in.8-µm CMOS technoloy. A ain of ~4 db, noise fiure of 4.4~4.78 db and IIP3 of -.3~-.4 dbm are achieved for all three bands in this desin with a minimum inter-band ain suppression of 8 db. EFEENCES [] S. Wu, and B. azavi, A 9-MHz/.8-GHz CMOS receiver for dual-band applications, IEEE Journal of Solid-State Circuits, vol. 33, pp. 78-8, December 998. [] H. Hashemi, and A. Hajimiri, Concurrent multiband low-noise amplifiers theory, desin, and applications, IEEE Transactions On Microwave Theory and Techniques, vol., no., pp. 88-3, January. [3] S. Andersson, C. Svensson, and O. Drue, Wideband LNA for a multistandard wireless receiver in.8 µm CMOS, Proceedins of the 9th European Solid-State Circuits Conference 3 (ESSCIC '3), pp. 6-68, September 3. [4] A. Bevilacqua, and A. M. Niknejad, An ultrawideband CMOS low-noise amplifier for 3.-.6GHz wireless receivers, IEEE Journal of Solid-State Circuits, vol. 39, no., pp. 9-68, December 4. []. A. Baki and M. N. El-Gamal, A.V multiiahertz CMOS tunable imae reject notch filter, The 4th International Conference on Microelectronics (ICM), pp , December. [6] S. J. Won, Y. J. Zhen, X. J. Tu and Y. Xu, A novel.4ghz CMOS interated LNA/notch filter with 6dB of imae rejection, Proceedins of the th IEEE International Symposium on Interated Circuits, Devices & Systems 4, F4_89D, Sinapore. [7] A. Ismail and A. A. Abidi, A 3--GHz low-noise amplifier with wideband LC-ladder matchin network, IEEE Journal of Solid- State Circuits, vol. 39, no., pp , December 4. [8] G. Gramena, M. Paparo, P. G. Erratico and P. De Vita, A sub-- db NF±.3-kV ESD-Protected 9-MHz CMOS LNA, IEEE Journal of Solid-State Circuits, vol. 36, no. 7, pp. -7, July. TABLE II PEFOMANCE SUMMAY AND COMPAISON WITH PEVIOUSLY PUBLISHED LNAS S ef. CMOS Process Frequency max NF min S max IIP3 Power FOM [db] [db] [db] [dbm] [mw] [/mw].4 GHz [].3-µm. GHz [3].8-µm ~7 GHz µm 3.~ standard GHz [4] 9.8-µm twinwell 3.~ GHz This Work.8-µm 94 MHz GHz GHz