Inter national J our nal of Electrical and Computer Engineering (IJECE) V ol. 8, No. 2, April 2018, pp. 926 932 ISSN: 2088-8708 926       I ns t it u t e  o f  A d v a nce d  Eng ine e r i ng  a nd  S cie nce   w     w     w       i                       l       c       m     A 60 GHz CMOS P o wer Amplifier f or W ir eless Communications T uan Anh V u VNU Uni v ersity of Engineering and T echnology , V ietnam Article Inf o Article history: Recei v ed September 7, 2017 Re vised December 28, 2017 Accepted: Jan 29, 2018 K eyw ord: Po wer Amplifier 60 GHz V -band W ireless Communication Millimeter -w a v e ABSTRA CT This paper presents a 60 GHz po wer amplifier (P A) suitable for wireless communications. The tw o-stage wideband P A is f abricated in 55 nm CMOS. Measurement results sho w that the P A obta ins a peak g ain of 16 dB o v er a -3 dB bandwidth from 57 GHz to 67 GHz. It archi v es an output 1 dB compression point (OP1dB) of 4 dBm and a peak po wer added ef ficienc y (P AE) of 12.6%. The P A consumes a total DC po wer of 38.3 mW from a 1.2 V supply v oltage while its core occupies a chip area of 0.45 mm 2 . Copyright c 2018 Institute of Advanced Engineering and Science . All rights r eserved. Corresponding A uthor: Name: T uan Anh V u Af filiation: VNU Uni v ersity of Engineering and T echnology Address: 144 Xuan Thuy Rd., Cau Giay Dist., Hanoi, V ietnam Phone: +84-4-3754-9338 Email: tanhvu@vnu.edu.vn 1. INTR ODUCTION W ireless communications using the millimeter -w a v e band ha v e been gro wing in the past fe w years due to its high data-rate transmiss ion capability . The demands for high data-rate short range wireless communication ha v e attracted a great deal of interest in the design of 60 GHz systems. As a result, the Federal Communications Commission (FCC) of the United States has of ficially appro v ed the spectrum utilization for 57 GHz to 64 GHz for commercial use. CMOS P A is among the most challenging b uilding blocks in implementing a 60 GHz system. The main purpose of a P A design is to pro vide suf ficiently high output po wer , while another important tar get is to achie v e high ef ficienc y . There are se v eral obstacles which mak e the implementations of a P A v ery dif ficult in CMOS technology . The use of submicron CMOS increases the dif ficulty of implementation due to technology limitations such as lo w breakdo wn v oltage and poor transconductance. The linearity and po wer ef ficienc y are lo wer than other technologies. Ho we v er , wit h the trend of lo wer po wer transmitters in the ne xt generation, implementation of CMOS P As with good ef ficiencies are becoming realistic despite steadily declining field-ef fect transistor (FET) breakdo wn v oltages. In this paper , we are going to present the designs and measurement results of a 60 GHz P A tar geted for wireless communications. The paper is or g anized as follo ws. Section 2 presents fundamentals of po wer amplifiers. Section 3 introduces the architecture of the proposed 60 GHz P A including a detailed description of the circuit topology . The measurement results are presented in section 4 and conclusions are gi v en in the last section. 2. PO WER AMPLIFIER B ASICS 2.1. P A Block Diagram The general design concept of a P A is gi v en in Fig. 1. The tw o port netw ork is applied in the design consisting of tw o matching netw orks that are used on both sides of the po wer transistor . Maximum g ain will be real- ized when the matching netw orks pro vide a conjug ate match between the source/load impedance and the transistor impedances [1]. Specifically , the matching netw orks transform the input and output impedances Z 0 to the source and J ournal Homepage: http://iaescor e .com/journals/inde x.php/IJECE       I ns t it u t e  o f  A d v a nce d  Eng ine e r i ng  a nd  S cie nce   w     w     w       i                       l       c       m     DOI:  10.11591/ijece.v8i2.pp926-932 Evaluation Warning : The document was created with Spire.PDF for Python.
IJECE ISSN: 2088-8708 927 T able 1. Conduction angles of the dif ferent current-mode P A classes Class Conductance Angle A 2 AB –2 B C 0– load impedances Z S and Z L , respecti v ely . Both input and output matching netw orks are designed for 50 e xternal load. Figure 1. Block diagram of a P A. 2.2. Classification of P As There are generally tw o types of P As: the current source mode P A and the switching mode P A. Dif ferent kinds of each mode of P As and their functional principles are introduced in detail in [2]. In the current source mode P A, the po wer de vice is re g arded as a current source, which is controlled by the input signal. The most important current source mode P As are class A, class B, class AB and class C. The y dif fer from each other in the operating point. Fig. 2 illustrates the dif ferent classes of the current source mode P A in the transfer characteristic of a FET de vice. The drain current I D e xhibits pinch-of f, when the channel is completely closed by the g ate-source v oltage V GS and reaches the saturation, in which further increase of g ate-source v oltage results in no further increase in drain current. The other v ery important concept to define the dif ferent classes of the current source mode P A is the conduction angle . The conduction angle depicts the proportion of the RF c ycle for which conduction occurs. The conduction angles of dif ferent classes are summarized in table 1. Figure 2. Operating points of dif ferent current-mode P As classes. 2.3. P A Efficiency Ef ficienc y is a measure of performance of a P A. The performance of a P A will be better if its ef ficienc y is higher , irrespecti v e of its definition. The P A is the most po wer -consuming block in a wireless transcei v er . Its po wer 60 GHz CMOS P ower Amplifier Evaluation Warning : The document was created with Spire.PDF for Python.
928 ISSN: 2088-8708 ef ficienc y has a direct impa ct on the battery life of mobile de vices. Se v eral definitions of ef ficienc y are commonly used with P As. Most widely used measures are the drain ef ficienc y and po wer added ef ficienc y . The drain ef ficienc y is defined as = P OUT P DC (1) where P OUT is the RF output po wer at operating frequenc y and P DC the DC po wer consumption of the P A output stage. It re v eals ho w ef ficient the P A is when it con v erts the po wer from DC to A C. The P AE is gi v en by P AE = P OUT P IN P DC (2) where P IN is the input po wer fed to the P A and P DC the total DC po wer consumption of the P A. The P AE gets close to if the g ain of the P A is suf ficient high so that the input po wer is ne gligible. 3. DESIGN OF 60 GHz PO WER AMPLIFIER The 60 GHz P A is designed using 55 nm CMOS process pro vided by Fuji tsu Ltd. Its back end consists of 11 copper layers and a top aluminum redistrib ution layer (RDL). The cross-vie w of a grounded coplanar w a v e-guide transmission line (GCPW -TL) is depicted in Fig. 3 [3]. The GCPW -TL with the characteristic impedance of 50 (the 5 0 GCPW -TL) is used for shunt and series stubs of the matching netw orks and for connecting to the input and output pads of the 60 GHz P A. Its signal line consists of the RDL layer with a width of 8 µm. Ground (GND) w alls composed of the 6th to 11th metal layers with a width of 9 µm are placed on the both side of the signal line at the distance of 11.5 µm. The 3rd to 5th metal layers are meshed and stitched together with vias to form the GND plane. Figure 3. The cross-vie w of the 50 GCPW -TL. The complete circuit of the proposed P A with all component v alues are gi v en in Fig. 4. It includes an input matching netw ork, an output matching netw ork, tw o common-source based amplifying stages and an inter - stage matching netw ork. F or bandwidth enhancement, multi-stage matchings using capacitors and GCPW -TLs are adopted. The series capacitors and GCPW -TLs form 4th-order and 2nd-order high-pass filters at the input and output of the P A, respecti v ely . The input is matched to 50 for measurement purpose while the load is optimized for maximizing output po wer using load-pull simulation. The inter -stage matching netw ork is based on the PI netw ork for wideband performance. A 128 resistor is added in series to the transistor’ s g ate of the first amplifying stage for stabilization. The minimum-loss cascade stabilizing resistor v alue is det ermined from the Smith chart by finding the constant resistance that is tangent to the appropriate stability circle [4]. All of the capacitors also act as coupling capacitors while the DC bias v oltages are applied through t he shunt GCPW -TLs. The bias v oltages are common to all amplifying stages. The connection between the MOSFETs, MOM capacitors and GCPW -TLs are made by the 10th and 11th metal layers. The lengths of the GCPW -TLs and the MOM capacitor v alues are determined by a nonmetric optimization process taki ng into account the models of MOSFETs, MOM capacitors and GCPW -TLs. The parasitic components are e xtracted using bond-based design which is a measurement-based design approach to a v oiding the dif ficulty associated with layout parasitics when ordinary layout parasitic e xtraction (LPE) tools used for chip design do not e xtract inductances [5]. The f ar end of each shunt stub is terminated by a wideband decoupling po wer line with v ery lo w characteristic impedance (the 0 TL) [6]. IJECE V ol. 8, No. 2, April 2018: 926 932 Evaluation Warning : The document was created with Spire.PDF for Python.
IJECE ISSN: 2088-8708 929 Figure 4. The proposed 60 GHz P A. 4. MEASUREMENT RESUL TS In order to v erify the performance of the 60 GHz P A, a chip prototype w as f abricated in 55 nm CMOS. Fig. 5 sho ws the die microphotograph of the P A. The P A occupies an area of 0.72 0.63 mm 2 including probe pads. The P A w as measured by means of on-chip probings using a probe station. The RF probe pads were designed for ground-signal-ground (GSG) probes with 750 µm pitch. The Anritsu 37397D VN A and V -band frequenc y e xtenders were used for measuring small-signal S-parameters. Figure 5. The die microphotograph of the 60 GHz P A. Fig. 6 sho ws the measured and simulated S-parameters of the 60 GHz P A. As can be seen in this figure, the measured results sho w good agreements with the simulated ones. Both input and output return loss indicate wideband performance when S 11 and S 22 remain belo w -10 dB o v er almost of the -3 dB bandwidth from 57 GHz to 67 GHz. The 60 GHz P A achie v es a peak g ain of 16 dB at 61 GHz. The re v erse isolation is lo wer than -20 dB (not sho wn in the figure). A high re v erse isolation guarantees high stability for the P A. Fig. 7 plots the output po wer v ersus the input po wer . A K e ysight E8244A signal generator and a V i v aT ech 60 GHz CMOS P ower Amplifier Evaluation Warning : The document was created with Spire.PDF for Python.
930 ISSN: 2088-8708 Figure 6. The measured and simulated S-parameter of the 60 GHz P A. VTXF A-06-12 signal module were used for generating input signal at 60 GHz while a VDI PM5-305V po wer sensor w as used to measure the output po wer . Due to the equipment limitation at V -band in our laboratory , the output po wer can only be measured up to -3 dBm of the input po wer . At 60 GHz, the designed P A obtains a OP1dB of approximately 4 dBm. Fig. 8 and Fig. 9 sho w the drain ef ficienc y and P AE v ersus the input po wers, respecti v ely . The designed P A archi v es a peak P AE of 12.6% at -3.5 dBm input po wer . The P A consumes a total po wer of 38.3 mW from a 1.2 V supply v oltage. T able 2 summarizes the performance of the proposed P A and compares it to other published ones operating in the similar frequenc y range. A popular figure-of-merit (F oM) used for comparison is defined as the g ain bandwidth product (GBWP) di vided by the DC po wer consumption ( P DC ). Figure 7. The measured and simulated output po wer v ersus the input po wer of the 60 GHz P A. 5. CONCLUSIONS In this paper , we ha v e presented the designs and measurement results of the 60 GHz P A tar geted for wireless communications. The proposed P A obta ins the peak g ain of 16 dB while the -3 dB bandwidth co v er the entire of the IJECE V ol. 8, No. 2, April 2018: 926 932 Evaluation Warning : The document was created with Spire.PDF for Python.
IJECE ISSN: 2088-8708 931 Figure 8. The measured and simulated drain ef ficienc y of the 60 GHz P A. Figure 9. The measured and simulated P AE of the 60 GHz P A. T able 2. Comparison with pre vious published P As operating in the 60 GHz frequenc y band P arameter RFIC’10 [7] APMC’12 [8] RFIT’15 [9] T -MTT’13 [10] MWCL ’15 [11] This w ork CMOS T echnology 65 nm 65 nm 65 nm 65 nm 65 nm 55 nm No. of Stages 3 2 3 4 3 2 Gain (dB) 30 12.1 20 20 20 16 -3 dB BW(GHz) 7 7 8 4.5 15 10 Peak P AE (%) 18 11.1 14 6.6 9 12.6 Die Area (mm 2 ) 0.06 0.61 0.56 2.25 0.7 0.45 OP1dB (dBm) 6.8 4.5 10.4 13.5 5 4 Po wer Cons. (mW) 65 45.8 93 480 60 38.3 GBWP/ P DC 3.41 0.62 0.86 0.09 2.5 1.65 60 GHz CMOS P ower Amplifier Evaluation Warning : The document was created with Spire.PDF for Python.
932 ISSN: 2088-8708 60 GHz frequenc y band. It e xhibits the OP1dB of 4 dBm and the peak P AE of 12.6%. The total po wer consumption of the P A is 38.3 mW while it occupies the chi p area of 0.45 mm 2 including probe pads. The performances of the designed P A are competiti v e to other state-of-the-art P As in CMOS. REFERENCES [1] G. Gonzalez, ”Micro w a v e T ransistor Amplifiers - Analysis and Design/Second Edition, Prentice Hall, Inc. , 1997. [2] S. C. Cripps, ”RF Po wer Amplifier for W ireless Communications”, Artech House, Inc. , 1999. [3] S. Hara, I. W atanabe, N. Sekine, A. Kasamatsu, K. Katayama, K. T akano, T . Y oshida, S. Amaka w a, and M. Fujishima, Compact 138-GHz Amplifier with 18-dB Peak Gain and 27-GHz 3-dB Bandwidth, 2015 IEEE Inter - national Symposium on Radio-Frequenc y Inte gration T echnology (RFIT 2015) , pp. 5557, August 2015. [4] R. Gilmore and L. Besser , Practica l RF Circuit Design for Modern W ireless Systems - V olume II: Acti v e Circuits and Systems, Artech House Inc. , 2003. [5] M. Fujishima, M. Moto yoshi, K. Katayama, K. T akano, N. Ono, and R. Fujimoto, 98 mW 10 Gbps W ireless T ranscei v er Chipset with D-band CMOS Circuits, IEEE Journal of Solid-State Circuits , v ol. 48, no. 10, pp. 22732284, October 2013. [6] S. Amaka w a, R. Goda, K. Katayama, K. T akano, T . Y oshida, and M. Fujishima, W ideband CMOS Decoupling Po wer Line for Millimeter -w a v e Applicationss, 2015 IEEE MTT -S International Micro w a v e Symposium (IMS 2015) , pp. 1-5, May 2015. [7] M. Boers, A 60 GHz T ransformer Coupled Amplifier in 65nm Digi tal CMOS, 2010 IEEE Radio Frequenc y Inte grated Circuits Symposium (RFIC 2010) , pp. 343346, May 2010. [8] R. Minami, K. Bunsen, K. Okada, and A. Matsuza w a, A 60 GHz Po wer Amplifier Using High Common-mode Rejection T echnique, 2012 Asia- P acific Micro w a v e Conference (APMC 2012) , pp. 1012, December 2012. [9] D. Li, L. Zhang, and Y . W ang, Design of 60-GHz Amplifiers Based on Ov er Neutralization and Optimized Inter -stage Matching Netw orks in 65-nm CMOS, 2015 IEEE International Symposium on Radio-Frequenc y Inte gration T echnology (RFIT 2015) , pp. 130132, August 2015. [10] S. Aloui, B. Leite, N. Demirel, R. Plana, D. Belot, and E. K erherv e, High-g ain and Linear 60-GHz Po wer Am- plifier with a Thin Digital 65-nm CMOS T echnology , IEEE T ransactions on Micro w a v e Theory and T echniques , v ol. 61, no. 6, pp. 24252437, June 2013. [11] H. Zhang and Q. Xue, 60 GHz CMOS W ideband Dif ferential Dri ving Amplifier Us ing Multi-Section Coupled Lines, IEEE Micro w a v e and W ireless Components Letters , v ol. 25, no. 9, pp. 600602, September 2015. BIOGRAPHY OF A UTHOR T uan Anh V u recei v ed the B.S de gree and M.Sc de gree in Electronics and T elecommunications T echnology from Uni v ersity of Engineering and T echnology , V ietnam National Uni v ersity in 2006 and 2009, respecti v ely . In 2013, he recei v ed Ph.D de gree in the field of analog/mix ed-signal RF nanoelectronics from Uni v ersity of Oslo, Norw ay . Since 2014, he has been a lecturer at F aculty of Electronics and T elecommunications, VNU Uni v ersity of Engineering and T echnology . Dr . T uan Anh V u w as with Department of Semiconductor Electronics and Inte gration Science, Hiroshima Uni v ersity as a postdoctoral researcher for one year . He is no w doing postdoc at Department of Electrical and Computer Engineering, Uni v ersity of California, Da vis . His research interests are analog RF inte grated circuit designs including po wer amplifiers, lo w noise amplifiers, mix ers, fre- quenc y multipliers, etc. IJECE V ol. 8, No. 2, April 2018: 926 932 Evaluation Warning : The document was created with Spire.PDF for Python.