Frequency response

About: Frequency response is a research topic. Over the lifetime, 25705 publications have been published within this topic receiving 332249 citations.

Design of Robust Digital Stabilizing Controller for Fourth-Order Boost DC–DC Converter: A Quantitative Feedback Theory Approach

Abstract: In this paper, we have proposed a quantitative feedback theory based robust digital voltage mode controller for a fourth-order boost dc-dc converter operating in continuous conduction mode. Discrete-time models of the converter are established for triangular trailing-edge modulation, which is then used in the compensator design. It is observed that an up-down glitch is present in the frequency response of control-to-output transfer functions of higher order dc-dc converters, and because of this, gain margin (GM) and phase margin (PM) alone are unable to give correct information about closed-loop stability. Therefore, in this paper, we have introduced a safety margin as an additional design specification, which along with GM and PM information reflects the actual stability of the higher order dc-dc converters. A simplification in loop-shaping approach is also proposed, which considerably reduces the time and effort involved in loop-shaping as compared to present trial-and-error-based approach and also results in a robust compensator of feasible order. Robustness of the designed controllers is analyzed in frequency and time domains through computer simulations and is then verified experimentally on a 28-V 30-W laboratory prototype converter. The experimental results are in line with the analytical design studies and demonstrate that the controller, which is directly designed through a discrete-time model, is more robust than an average model-based digitally redesigned controller.

A built-in self-test strategy for wireless communication systems

Abstract: Wireless communication is a rapidly expanding field and considerable research effort is underway. Electronic system manufacturers are actively trying to incorporate all of the RF, IF and baseband functions on the fewest possible ICs so as to reduce system size and cost, and to improve overall system performance. Unfortunately, without a coherent test strategy, any cost reduction gained by miniaturization will be offset by increased testing costs. In this work we propose a built-in self-test scheme for bandpass type systems such as those used in wireless communication devices. The scheme is centered around a high frequency oscillator based on bandpass delta-sigma modulation techniques and a digital extraction method. We will show through experiments that measures meaningful to the analog test engineer such as signal-to-noise ratio, frequency response and intermodulation distortion are obtainable with this method.

Time resolved optical array detectors and CCD cameras for frequency domain fluorometry and/or phosphorimetry

Abstract: An apparatus for cross-correlation frequency domain fluorometry-phosphorimetry comprises a source of electromatic radiation and means for amplitude modulating the radiation at the first frequency. The amplitude modulated radiation is directed at a sample, while an optical array detector measures the resulting luminescence of the sample. A signal is provided coherent with the amplitude modulated electromagnetic radiation signals, at a second frequency which is different from the first frequency. The apparatus has the capability for shutting off and turning on the coherent signal at the second frequency in a cycle which is at a third frequency that is different from the difference between the first and second frequencies. This produces a resultant signal at a frequency derived from the difference and the third frequency. The resultant signal, when turned on, modulates the gain of the detecting means or multiplies its output, depending upon the nature of the detecting means. The amount of luminescence measured by the optical array detector is read when the coherent signal is off in its cycle of the third frequency. A signal from the reader described above is then detected at a frequency of the resultant signal to determine phase shift and modulation changes of the luminescence.

Pendulum as Vibration Absorber for Flexible Structures: Experiments and Theory

Abstract: The dynamic response ofa beam-tip mass-pendulum system subjected to a sinusoidal excitation is investigated. A simple pendulum mounted to a tip mass of a beam is used as a vibration absorber. The nonlinear equations of motion are developed to investigate the autoparametric interaction between the first two modes of the system. The nonlinear terms appear due to the curvature of the beam and the coupling effect between the beam and pendulum. Complete energy transfer between modes is shown to occur when the beam frequency is twice the pendulum frequency. Experimental results are compared with a theoretical solution obtained using numerical integration. The experimental results are in qualitative agreement with the theory.