Microwave Traveling Wave Amplifiers and Distributed Oscillators ICs in Industry Standard Silicon CMOS Kalyan Bhattacharyya Supervisors: Drs. J. Mukherjee and M. Shojaei EE, IIT, Bombay

2 Contents l Introduction l Coplanar Waveguide (CPW) l Traveling Wave Amplifier (TWA) l TWA Based Distributed Oscillator (DO) l Conclusion

3 Why CMOS? Low Cost l 50 GHz cut-off frequency for 0.18µm technology l Maturity of process technology l Higher thermal conductivity l Mechanical stability of substrate l Ease of high level integration

4 Introduction l Traveling Wave Amplifier (TWA) is for constant gain over a broad frequency range (applic. in high speed networks) Designs use the parasitic capacitances of the active devices that typically limit the high-frequency performance coplanar waveguides (CPW) as on-chip inductors A Distributed Oscillator operates in the forward gain mode of a TWA, our designs use only n-FETs, CPWs and a loop we called ‘folded CPW’

5 Amplifier with Spiral Inductors l Replace large area inductors with coplanar waveguides l Reduce and use parasitic capacitances in amplifier

6 CMOS on silicon presents some challenges for RF design: l Lossy substrate and low impedance transmission lines l Low electron mobility in Si l High gate resistance l Low output impedance at the drain l Low transconductance in Si FETs Design Challenges

7 Distribution of Gain Producing Cells l Formation of Gate and Drain Artificial Transmission Lines l RF signal travels down the gate line l Each n-FET transfers signal to drain line through its transconductance l Signals add in drain line in forward propagating direction Basic TWA with CPW as Inductors

8 Coplanar Waveguide L=0.5 mm T line T OX Silicon substrate W S

9 Layout of Coplanar Waveguide Measured Loss = 0.32dB at 10GHz Kalyan Bhattacharyya et al, IEEE Microwave and Wireless Components Letters, Jan, 2004

10 Gain Cells of the ICs and One Element of Artificial Transmission Line

11 Bandwidth of TWA in 0.18micron CMOS L-H Lu et al; IEEE Microwave and Wireless Components Letters, Nov,

12 TWA Based Oscillator Design: OSC-1 l Feedback connection from TWA output to input [1][2] l The length of feedback connection is critical l Measured Oscillation Frequency: 12 GHz l Output Level: 5.77 dBm, n-FET width: 60 micron l Phase Noise: MHz offset Kalyan Bhattacharyya et al; IEEE RAWCON 2004 and WAMICON 2005

13 TWA-based Distributed OSC-1 Layout Size: 1.5x0.642 sq. mm (including the measuring pads)

14 Coplanar test structure ‘folded CPW’

15 Measured Loss of ‘folded CPW’ Loss: dB at 10 GHz before pad deembedding

16 Measured Reflections of ‘folded CPW’ S 11 = dB and S 22 = -24 dB at 12GHz

17 Measured power spectrum of Osc-1 Fundamental is at 12.00GHz, +5.77dBm Second harmonic at 23.92GHz, -34 dBm l Bias: 1.8V / 60mA

18 Measured phase noise of Osc-1 PN = dBc/Hz at 1 MHz offset from the 12GHz carrier l Figure of Merit [9] = dBc/Hz

19 Operating Frequency (GHz) Power level (dBm) Bias Voltage, V Technology and Reference µm CMOS, [1] µm BiCMOS, [5] µm BiCMOS, [5] µm CMOS, This work Comparison of Power Level of Si DO

20 VCO-Like Simulation for OSC-1 with C c l Coupling capacitor allows the independent control of the dc voltage in the gate and drain lines l VCO operation by tuning the parasitic gate and drain capacitances (‘inherent varactors’ [5]) of the n-FETs Single n-FET gain cell with n-FET width of 30 micron V DS = 1.8V, V GS = 1.2V, Freq = GHz, Power = 5.1dBm V DS (V)V GS (V)Frequency Change (MHz) Power Change (dBm) 2.0V1.2V60 MHz+1 dBm 1.8V1.060 MHz-1.3 dBm

21 Cascode Cells DO: OSC-2 l Simulated Oscillation Frequency: GHz, with 4-stages of cascode gain cells Kalyan Bhattacharyya et al, IEEE RAWCON’04 and WAMICON’05 l A New circuit for DO Design l Higher Output Level expected for OSC-2 than OSC-1, when both 5 –stages

22 Static Frequency Changing by Varying L Changed Values of Inductive CPWs from: L D1 = L G1 = L D2 = L G2 =L/2, L D3 = L G3 =L OSC-2 Freq: (GHz) OSC-1 Freq: (GHz) L D1 =3L/ L D1 =L L G1 =3L/ L G1 =L L D1 =L G1 =3L/ L D1 = L G1 =L L D2 =3L/ L D2 =L L G2 =3L/ L G2 =L L D2 =L G2 =3L/ L D2 = L G2 =L L D3 =3L/ L D3 =2L L G3 =3L/ L G3 =2L L D3 =L G3 =3L/ L D3 = L G3 =2L

23 Conclusions l Coplanar Waveguides and folded CPW used for Distributed Oscillators in industry-standard CMOS l OSC-1, high Power Level of +5.77dBm at 12 GHz for Silicon DO  Phase noise of –115.16dBc/Hz at 1 MHz l A new distributed oscillator is proposed (RAWCON 2004) where each gain cell uses an n-FET cascode l Frequency variation of DOs by non-uniform transmission lines changing one or two L values l VCO-Like simulation using MOS VARACTORs at IIT, Bombay

24 REFERENCES [1] B. Kleveland, “CMOS interconnects beyond 10 GHz,” PhD thesis, Stanford University, August [2] Behzad Razavi, “Design of Integrated Circuits for Optical communications,” McGraw Hill, New York, [3] Kalyan Bhattacharyya and Ted Szymanski, “Performance of a 12GHz Monolithic Microwave Distributed Oscillator in 1.2V 0.18µm CMOS with a New Simple Design Technique for Frequency Changing,” IEEE Wireless and Microwave Technology Conference, WAMICON’2005, Clearwater, Florida, USA, April 7 and 8, 2005, pp [4] H. Wu and A. Hajimiri, “Silicon-Based Voltage-Controlled Oscillators,” IEEE Journal of Solid- State Circuits, vol. 36, No. 3, pp , March [5] Kalyan Bhattacharyya’s MASc Thesis, Department of Electrical and Computer Engineering, McMaster University, Hamilton, Ontario, Canada, June [6] Yuhua Cheng, M. Jamal Deen and C-H. Chen, “MOSFET Modeling for RF IC Design,” IEEE Transaction on Electron Devices, vol. 52, No. 7, July [7] Kalyan Bhattacharyya and M. Jamal Deen, “Microwave CMOS traveling wave amplifiers – performance and temperature effects,” IEEE Microwave and Wireless Components Letters, vol. 14, No. 1, pp , January [8] Kalyan Bhattacharyya and Ted Szymanski, “1.2V CMOS 1-10GHz Traveling Wave Amplifiers Using Coplanar Waveguides as On-Chip Inductors,” IEEE Radio and Wireless Conference (RAWCON), Atlanta, Georgia, USA, pp , September 19-22, [9] T. Y. Kim, A. Adams, N. Weste, “High performance SOI and bulk CMOS 5GHz VCOs,” IEEE Radio Frequency Integrated Circuits (RFIC) Symposium, pp. 93 – 96, 8-10 June 2003.

25 Thank You