A new high-efficiency, linear power amplification design technique derived from nonlinear dynamical systems

This paper describes the design and simulation results of a new concept in power amplification called Syncrodyne power amplification. Here we describe the design procedure for our Series-3 power amplifier for GSM waveforms. The foundation of this design has its basis in a subset of nonlinear behavior called chaotic dynamics. Since the groundbreaking publication by Ott, Grebogi, and Yorke [1] on control of chaotic systems, a great deal of work has been done in communication using chaos [2] [3], weak signal detection [4], and synchronization [5], among many other things. We first reported on the formulation, simulation, and experimentation of the Syncrodyne amplification technique for a 2-MHz system [6], then proposed and simulated an 800-MHz design using a heterojunction bipolar transistor (HBT) [7]. Since then, we’ve developed a method to apply this technique for the power amplification of GSM waveforms. Figure 1 shows a block diagram of the Syncrodyne Power Amplifier. The general concept is that a small input signal induces a chaotic oscillator of sufficiently higher power to take on its behavior via synchronization. The breakthrough realization was that a chaotic oscillator can be synchronized to a non-chaotic oscillation, and thereby take on the behavior of an arbitrary waveform. A modified Colpitt’s oscillator designed by Cicarrelli [8] was used as the central oscillator. Although this oscillator was not designed to be chaotic, it is well documented that an oscillator of Colpitts topology can produce chaotic oscillations [9]. Figure 2 shows the frequency content of the output of the free running chaotic oscillator. It shows the broad spectral content that is indicative of chaotic behavior as well as a peak at fundamental frequency of 860 MHz . We show that the gain is directly related to the coupling characteristics of the chaotic system, governed by the unstable manifolds [10], while the high efficiency is a result of operating the transistor in strongly nonlinear region of operation, thereby maximizing the voltage and current swings. Figure 3 shows the frequency content of the amplifier output. To date, our simulation gives results of 16-dB gain, 50% PAE, with harmonics at least 30- dB down from the fundamental. We continue to push the performance limits and are currently developing the prototype device for applications in cellular handsets and base stations that demonstrate 70% PAE or better. REFERENCES [1] E. Ott, C. Grebogi, J. A. Yorke, Phys. Rev. Lett. 64, 1196 (1990). [2] S. Hayes, C. Grebogi, E. Ott, Phys. Rev. Lett. 70, 3031 (1993). [3] H. Dedieu, M.P. Kennedy, and M. Hasler, “Chaos shift keying; Modulation and demodulation of a chaotic carrier using self-synchronizing Chua’s circuit,” IEEE Transactions on Circuits and Systems I, vol. 40, pp. 634-642, 1993. [4] C. M. Glenn, S. Hayes, Weak Signal Detection by Small-Perturbation Control of Chaotic Orbits, 1996 IEEE-MTT Symposium Digest (June 1996). [5] L. M. Pecora and T. L. Carroll, Synchronization in Chaotic Systems, Phys. Rev. Lett. 64, 821 (1990). [6] C. M. Glenn, Synthesis of a Fully-Integrated Digital Signal Source for Communications from Chaotic Dynamics-based Oscillations, Doctoral Dissertation, The Johns Hopkins University, January 2003. [7] C. M. Glenn, High-Gain, High-Efficiency Power Amplification for PCS, International Symposium on Advanced Radio Technology Digest, March 2003. [8] S. Cicarelli, Development of a Digital Wireless Communication System for Security Sensor Applications, Defense Nuclear Agency (Jan 1998) [9] Francis Moon, Chaotic Vibrations, Wiley & Sons, New York, 1987. [10] Edward Ott, Chaos in Dynamical Systems, Cambridge Univ. Press, Canada, 1993.

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