Oscillator
Oscillator Basics and Low-Noise Techniques for Microwave Oscillators and VCOs
Ulrich L. Rohde∗ (ulr@synergymwave.com) Chairman, Synergy Microwave Corporation
GaAs 2000 – Paris, France 2-6 October 2000
Abstract Microwave oscillator design is based on the principle of generating a negative resistance to compensate for the losses of the resonator. Several circuit combinations, including one- and twoport oscillators, are possible. In this discussion, we will first evaluate the conditions of oscillation for the Colpitts and Clapp-Gouriet oscillator. We will then evaluate a 19-GHz SiGe-based oscillator by assuming values, backed up by available S parameters and dc I-V curves, that we assigned to the nonlinear BFP520 model. So far it has been difficult to obtain complete documentation on modeling for the SiGe transistors, but our approximation appears to be justified. Next, we will evaluate a ceramic-resonator-based oscillator and show its performance. Going up to higher frequencies, we will introduce a 47-GHz lumped-resonator oscillator and a VCO at the same frequency that uses GaAsFETs as varactors. In all cases, we will give a thorough treatment of the circuits and their performance. Introduction This presentation will give an overview of both bipolar and GaAsFET-based oscillators, including ceramic-resonator oscillators (CROs). Its purpose is to show not only the linear/nonlinear mathematics, but also how the actual design should be considered, as well as commentary on the results. Many of the predictions can only be obtained by using appropriate software; for this purpose, we have used a harmonic-balance simulator by Ansoft. We also will show some practical circuits, both from the circuit design as well as the actual chip design. In the assumptions we have taken, we have avoided shortcuts so that the approach remains general in nature. It further needs to be pointed out that throughout this discussion, we will assume that each oscillator is followed by an
Ulrich L. Rohde∗ (ulr@synergymwave.com) Chairman, Synergy Microwave Corporation
GaAs 2000 – Paris, France 2-6 October 2000
Abstract Microwave oscillator design is based on the principle of generating a negative resistance to compensate for the losses of the resonator. Several circuit combinations, including one- and twoport oscillators, are possible. In this discussion, we will first evaluate the conditions of oscillation for the Colpitts and Clapp-Gouriet oscillator. We will then evaluate a 19-GHz SiGe-based oscillator by assuming values, backed up by available S parameters and dc I-V curves, that we assigned to the nonlinear BFP520 model. So far it has been difficult to obtain complete documentation on modeling for the SiGe transistors, but our approximation appears to be justified. Next, we will evaluate a ceramic-resonator-based oscillator and show its performance. Going up to higher frequencies, we will introduce a 47-GHz lumped-resonator oscillator and a VCO at the same frequency that uses GaAsFETs as varactors. In all cases, we will give a thorough treatment of the circuits and their performance. Introduction This presentation will give an overview of both bipolar and GaAsFET-based oscillators, including ceramic-resonator oscillators (CROs). Its purpose is to show not only the linear/nonlinear mathematics, but also how the actual design should be considered, as well as commentary on the results. Many of the predictions can only be obtained by using appropriate software; for this purpose, we have used a harmonic-balance simulator by Ansoft. We also will show some practical circuits, both from the circuit design as well as the actual chip design. In the assumptions we have taken, we have avoided shortcuts so that the approach remains general in nature. It further needs to be pointed out that throughout this discussion, we will assume that each oscillator is followed by an
References: 1. Aron Kain, Final Report for Bias Dependence Noise Modeling of Heterojunction Bipolar Transistors, USAF SBIR Phase II (PIIN), F33615-95-C-1707, November 1997. Issued by USAF/AFMC/ASC, Wright Laboratory WL/AAKE BLD 7, 2530 C ST, Wright-Patterson AFB, OH 45433-7607. 2. Robert A. Pucel and Ulrich L. Rohde, "An Accurate Expression for the Noise Resistance Rn of a Bipolar Transistor for Use with the Hawkins Noise Model," IEEE Microwave and Guided Wave Letters, Vol. 3, No. 2, February 1993, pp. 35-37. 3. Robert A. Pucel, W. Struble, Robert Hallgren and Ulrich L. Rohde, "A General Noise Deembedding Procedure for Packaged Two-Port Linear Active Devices," IEEE Transactions on Microwave Theory and Techniques, Vol. 40, No. 11, November 1993, pp. 2013-2024. 4. C. N. Rheinfelder et alia, "47-GHz SiGe MMIC Oscillator," 1999 IEEE MTT-S Digest, pp. 58. 5. V. Rizzoli, F. Mastri, and C. Cecchefti, "Computer-Aided Noise Analysis of MESFET and HEMT Mixers," IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-37, September 1989, pp. 1401-1410. 6. V. Rizzoli and A. Lippadni, "Computer-Aided Noise Analysis of Linear Multiport Networks of Arbitrary Topology," IEEE Transactions on Microwave Theory and Techniques, Vol. MTT33, December 1985, pp. 1507-1512. 7. V. Rizzoli, F. Mastri, and D. Masotti, "General-Purpose Noise Analysis of Forced Nonlinear Microwave Circuits," published in Military Microwave, 1992. 8. Ulrich L. Rohde, "Improved Noise Modeling of GaAs FETs," Microwave Journal, November 1991, pp. 87-101 (Part I) and December 1991, pp. 87-95 (Part II). 9. Ulrich L. Rohde, Chao-Ren Chang, and Jason Gerber, "Design and Optimization of LowNoise Oscillators Using Nonlinear CAD Tools," 1994 IEEE International Frequency Control Symposium, pp. 548-554. 10. Ulrich L. Rohde, "Oscillator Design for Lowest Phase Noise," Microwave Engineering Europe, May 1994, pp. 31-40. 11. Ulrich L. Rohde, Microwave and Wireless Synthesizers: Theory and Design (New York: John Wiley & Sons, 1997, ISBN 0-471-52019-5), Section 5-3 (Low-Noise Microwave Synthesizers) and Appendix B (A General-Purpose Nonlinear Approach to the Computation of Sideband Phase Noise in Free-Running Microwave and RF Oscillators). 12. Ulrich L. Rohde and David P. Newkirk, RF/Microwave Circuit Design for Wireless Applications, by John Wiley & Sons, April 2000, ISBN 0471298182. 13. F. X. Sinnesbichler et alia, "A 50-GHz SiGe HBT Push-Push Oscillator," 1999 IEEE MTT-S Digest, pp. 9-12. - 32 - 14. M. C. E. Yagoub and H. Baudrand, "Nonlinear Oscillator Design for Maximum Power," 1994 IEEE International Frequency Control Symposium, pp. 555-558. 15. M. Prigent et alia, "An Efficient Design Method of Microwave Oscillator Circuits for Minimum Phase Noise," IEEE Trans. Microwave Theory Tech., Vol. MTT-47, No. 7, July 1999, pp. 1123-1125. 16. M. Prigent and J. Obregon, "Phase Noise in FET Oscillators by low Frequency Loading and Feedback Circuitry Optimization," IEEE Trans. Microwave Theory Tech., Vol. MTT-35, Mar. 1987, pp. 127-129. 17. E. Vaury et alia, "A New Method for the Design of Ultra Low Noise Oscillators," in Int. Frequency Control Symp., Besançon, France, Apr. 1999. 18. Ulrich L. Rohde and Guenther Klage, “ Analyze VCOs and Fractional-N Synthesizers,” Microwaves & RF, August 2000, Pg. 57 - 33 -