Fundamental frequency

About: Fundamental frequency is a research topic. Over the lifetime, 8941 publications have been published within this topic receiving 131583 citations.

Design of Ultrawideband High-Efficiency Extended Continuous Class-F Power Amplifier

Abstract: Total bandwidth of existing wireless communication technologies covers a wide frequency range of over one octave. But most existing power amplifier configurations cannot meet this requirement while at the same time maintaining a high efficiency. Therefore, a new structure that can achieve multioctave bandwidth is proposed in this paper together with the design methodology. The difficulty in realizing a bandwidth larger than one octave lies in the overlapping of fundamental and harmonic frequencies. Regarding this problem, the continuous class-F mode is extended to allow a resistive second harmonic impedance, rather than the pure reactive one. With the relaxed design requirements and overlapping design space of fundamental and second harmonic frequencies, harmonic tuning and fundamental frequency matching networks can be designed separately. More importantly, broadband matching for fundamental frequencies can be implemented simply by considering only three fundamental frequency points using the multiple frequencies matching method. To verify the validity of the proposed methodology, a multioctave power amplifier was designed, fabricated, and measured. Measured results verify a wide bandwidth of 128.5% from 0.5 to 2.3 GHz. Over this frequency range, drain efficiency was larger than 60% with output power greater than 39.2 dBm and large signal gain larger than 11.7 dB.

Period-doubling systems as small-signal amplifiers.

Abstract: Near the onset of a period-doubling bifurcation, any dynamical system can be used to amplify perturbations near half the fundamental frequency: The closer the bifurcation point, the greater the amplification. An analytic expression for the frequency response curve is derived explicitly for the driven Duffing oscillator. Results of analog simulations are presented to check the main features of the theory. We propose that the superconducting Josephson parametric amplifier is an example of this amplification process.

A chirp-z transform-based synchronizer for power system measurements

Abstract: In the last few years, increased interest in power and voltage quality has forced international working groups to standardize testing and measurement techniques. IEC 61000-4-30, which defines the characteristics of instrumentation for the measurement of power quality, refers to IEC 61000-4-7 for the evaluation of harmonics and interharmonics. This standard, revised in 2002, requires a synchronous sampling of voltage or current signal, in order to limit errors and to ensure reproducible results even in the presence of nonstationary signals. Therefore, an accurate estimation of the fundamental frequency is required, even in the presence of disturbances. In this paper, an algorithm to detect the fundamental frequency is proposed; it is based on the chirp-z transform (CZT) spectral analysis and is able to observe all standards in force because of its accuracy and working characteristics. Theoretical aspects are discussed and various experimental tests are reported, comparing the proposed method with a similar well-known one based on interpolated fast Fourier transform (FFT) analysis. Finally, a complete characterization of the proposed system was performed, and its accuracy was evaluated by means of a calibrator.

Pulse Width Modulated Inverters for AC Motor Drives

Abstract: The use of pulse width modulation techniques applied to thyristor inverters to obtain variable frequency-variable voltage waveforms is reviewed. A number of basic modes of modulation are analyzed; harmonic content and principles of wave generation are investigated and compared to conventional forms of synthesis. The prime advantage of such systems is to preserve a near sine wave envelope rather than to eliminate specific harmonics. This allows a potentially wider range of speed control by keeping the harmonics in fixed but small proportions relative to the fundamental frequency. The principal harmonics which are presen-t are those induced by pulse modulation; these normally can be filtered by the inherent delays of the motor.

Spectral representation of a periodic nonstationary random process

Abstract: This paper deals with the periodic nonstationary process, the mean value and the correlation function of which are invariant under shift by a multiple of a certain period. The spectral representation is derived by making use of Loeve's harmonizability theorem on a second-order nonstationary process. The process is represented as a sum of infinite stationary processes among which covariances exist. Each stationary process has a nonoverlapping frequency band of equal width, the center of which corresponds to a harmonic of the fundamental frequency determined by the period. The correlation function, dependent on two points, is represented in terms of a matrix-valued spectral density that is hermitian and nonnegative definite. The representations in other possible forms are also given. Finally some properties, special processes, and examples produced by a certain stationary random sequence are discussed.