Fundamental Modulation Limits for Minimum Switching Frequency Inband-Error-Free High-Efficiency Power Amplifiers
ABSTRACT This paper explores the modulation bandwidth limits for switching amplifiers, by analyzing the fundamental tracking capabilities of two-level switching signals. With this aim, this work synthesizes two-level switching signals by obtaining the distribution of switching events providing both minimum average switching frequency and inband-error-free encoding, targeting to minimize the amplifier switching losses when tracking a generic bandlimited signal. This analysis also provides a framework reference to characterize the deviation from such limit in modulations used in actual amplifiers.
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ABSTRACT: A time encoding machine is a real-time asynchronous mechanism for encoding amplitude information into a time sequence. We investigate the operating characteristics of a machine consisting of a feedback loop containing an adder, a linear filter, and a noninverting Schmitt trigger. We show that the amplitude information of a bandlimited signal can be perfectly recovered if the difference between any two consecutive values of the time sequence is bounded by the inverse of the Nyquist rate. We also show how to build a nonlinear inverse time decoding machine (TDM) that perfectly recovers the amplitude information from the time sequence. We demonstrate the close relationship between the recovery algorithms for time encoding and irregular sampling. We also show the close relationship between time encoding and a number of nonlinear modulation schemes including FM and asynchronous sigma-delta modulation. We analyze the sensitivity of the time encoding recovery algorithm and demonstrate how to construct a TDM that perfectly recovers the amplitude information from the time sequence and is trigger parameter insensitive. We derive bounds on the error in signal recovery introduced by the quantization of the time sequence. We compare these with the recovery error introduced by the quantization of the amplitude of the bandlimited signal when irregular sampling is employed. Under Nyquist-type rate conditions, quantization of a bandlimited signal in the time and amplitude domains are shown to be largely equivalent methods of information representation.Circuits and Systems I: Regular Papers, IEEE Transactions on 11/2004; · 2.24 Impact Factor
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ABSTRACT: An efficiency-enhanced power-amplifier system design is presented based on wide-bandwidth envelope tracking (WBET) with application to orthogonal frequency-division multiplexing wireless local area network systems. Envelope elimination and restoration (EER) and WBET are compared in terms of the time mismatch sensitivity between the base-band amplitude path and the RF path, and it is demonstrated that WBET is much less sensitive than EER to these effects. An adaptive time-alignment algorithm for the WBET system is developed and demonstrated. The analysis and algorithm are verified by experimental results. The measurement shows that the peak drain efficiency of the complete system was 30% at a 2.4-GHz orthogonal frequency-division multiplexing output power of 20 dBm.IEEE Transactions on Microwave Theory and Techniques 05/2005; · 2.23 Impact Factor
Conference Proceeding: Bandwidth limits in PWM switching amplifiers[show abstract] [hide abstract]
ABSTRACT: PWM buck switching power converters are good candidates for high efficiency power amplification of arbitrary band-limited signals. The correlation between the signal bandwidth and the switching frequency, in turn related to switching losses, imposes practical limits for high bandwidth applications. Stringent specifications appear in such applications as audio amplifiers (kHz signal bandwidths), and lately, in fast envelope tracking power amplifiers (MHz signal bandwidths) for the Envelope Elimination and Restoration technique in polar RF power amplification. Bandwidth limitations in PWM amplifiers are explored in this work by proposing design criteria for obtaining the switching frequency to signal bandwidth ratio (f<sub>s</sub>/f<sub>x</sub>) so as to guarantee a given aliasing error. To achieve that purpose, PWM spectra are reviewed for single tone, two-tone and multitone signals. Subsequently, by taking into account the analogy between PWM and FM spectra, bandwidths around the switching frequency are estimated by extending Carson's rule to an arbitrary error. This allows obtaining an extension of the Nyquist criterion for pulse-width modulation. System-level simulation results are reported to validate the analysis, showing that the conventional f<sub>s</sub>/f<sub>x</sub> factor used in the power converter design field might be too conservativeCircuits and Systems, 2006. ISCAS 2006. Proceedings. 2006 IEEE International Symposium on; 06/2006