Showing papers on "Feedback loop published in 1969"

Direct-feedback coders: Design and performance with television signals

Abstract: Direct-feedback coding is a refinement on the well-known differential coding method. Two filters are used at the transmitter of a direct-feedback coder; one connected in series with the input and the other in the forward path of a feedback loop that contains the quantizer. The first filter preemphasizes the signal and determines the overload characteristic of the coder; the other filter shapes the quantization noise and sets the stability of the feedback. At the receiver a filter reconstitutes the signal spectrum and deemphasizes the noise. For television the preemphasis should he a short time-constant differentiator, the deemphasis a short time integrator, and the feedback filter a long time integrator. Conventional differential coders use a single filter in the feedback path both to provide preemphasis and to shape the feedback characteristic, so the design is a compromise. Compared with direct-feedback coding they usually have less feedback gain and a larger time constant in the preemphasis and deemphasis, consequently, the contouring noise is more visible and the streaking caused by transmission error is longer. Although only application to television is considered, the methods have wider use. General formulae are given for the output noise and optimum filter characteristics; they take into account signal spectra, frequency weighting for noise, sampling rate, quantization step size, and an overload parameter. Measurements on real coders, operating on TV signals, and digital simulations confirm the results.

Some results on the L p stability of linear time-varying systems

Abstract: This paper considers the L p stability of systems with a convolution operator in the forward loop and a time-varying gain in the feedback loop. A frequency-domain condition involving the frequency response of the forward loop and the Fourier coefficients of the time-varying gain of the feedback loop is presented. The paper also contains a somewhat more involved time-domain condition in terms of the open-loop weighting pattern.

A Generalization of Shift-Register Sequence Generators

Abstract: : The paper examines the questions of the existence and the design of feedback shift-register sequence generators (FSR) capable of producing sequences with periods longer than obtained by the classical linear or nonlinear feedback shift-register techniques. This capability is achieved by cyclically modifying the effective connections in the feedback loop. A description of the behavior of the classical n-stage FSR in terms of cyclic transformations on its state space X sub n is formulated and used to analyze the behavior of the proposed generalized n-stage feedback shift-register, the (m, n)-FSR. The latter is shown to be capable of producing sequences of maximal period m(2 raised to the n power) for any m and n by cyclic application of properly chosen transformations. (Author)

Time multiplexer with feedback

Abstract: Time-multiplexing networks for analog signals are subject to spurious transmissions such as leakage signals and switching transients. This disclosure proposes to solve these problems by the provision of a feedback path from the common portion of the network to each of the input branches, each feedback loop containing at least one active device. In addition to the above advantages, such a network realizes all of the usual advantages accruing from the application of feedback to an amplifier.

Analysis of Commutated Networks Employing Feedback Circuits

Abstract: A method of analysis has been developed for feedback systems employing commutated networks in the forward loop and linear transfer functions in the feedback loop. The method handles single-phase and polyphase commutated networks as well as coupled and uncoupled networks. Although commutated networks are linear from the superposition theory viewpoint, linear feedback theory is shown to be not applicable because of the harmonics present in the feedback loop. Techniques for simplifying the analysis of commutated networks by the use of equivalent block diagrams provide additional insights into commutated network operation.

Voltage measuring apparatus employing feedback gain control to obtain a predetermined output and a feedback loop to readout the gain value

Abstract: An unknown signal is directly measured by means of an electronic circuit having no mechanical moving parts. The root means square values of unknown AC signals over large ranges are readily determined by measuring the amplification of a compressor in the circuit with a DC voltage signal separated from the measured signal by means of simple filters.

Stability analysis of Apollo-Saturn V propulsion and structure feedback loop.

Abstract: Apollo-Saturn 5 propulsion and structure feedback loop, analyzing Pogo components and Nyquist plot application

Indirect electroheat regulation

Abstract: Electroheat regulation by means of on/off controllers is a commonly used regulation scheme. When the thermal process to be regulated has a large inherent time delay, or when it is not possible to have the temperature-sensing point at the output of the thermal process, another scheme, which consists of a feedback loop around a model, is suitable. This auxiliary process may be another thermal process or an electrical analogue of the main process. The main process is then controlled by open-loop control. It is shown that, by a suitable choice of the auxiliary-process parameters, better performance criteria can be obtained.

Derivative-Discontinuous Electroheat Control

Abstract: In electroheat processes such as induction furnaces, arc furnaces, radiant furnaces, plasma torches, fluidized beds, etc., that are usually discontinuously controlled (because of the large power ratings involved) a great deal of confusion has existed as to the effect of derivative signals in the primary feedback loop. This has resulted in empirical design rules for the derivative feedback in controllers for such processes. An analysis of the effect of derivative feedback upon the performance indices of such electroheat processes is presented. Methods of evaluating these indices for various combinations of command and derivative feedback are given, and the boundaries are clearly defined for the process instability that results from excessive derivative feedback. It is shown that the well-known cycling characteristic display is inadequate for conveying to the practicing engineer the effect of derivative feedback. Two new displays have been derived that clearly show the effect of command and derivative feedback upon the process performance. Finally, the optimum derivative feedback conditions are given for the typical electroheat process. Mathematical derivations have been avoided, and the presentation is intended for the professional engineer engaged in industrial electroheat control.

Stabilised electrical power supply equipment

Abstract: 1,155,814. Automatic control systems. STANDARD TELEPHONES & CABLES Ltd. April 10, 1968, No. 17376/68. Heading G3R. A regulated power supply of the type in which the magnitude of a D.C. output, e.g. voltage, current, or power, is maintained constant comprises a feedback loop the gain of which is controlled to provide maximum gain at the desired output level. As shown, a load 5 is supplied with constant current by the amplified, rectified and smoothed output from an amplitude comparator 2 which produces a series of pulses having a width related to the magnitude of an error signal derived from a feedback loop including a current sensing resistor 6, a reference source and a differential amplifier 7. The comparator 2 comprises two transistors connected as shown, the error signal being applied to the base of one transistor and a reference wave, e.g. of sawtooth form, being applied to the base of the other transistor, so that the comparator produces output pulses of duration equal to the period of time during which the instantaneous amplitude of the reference wave exceeds the magnitude of the error signal. The gain of the feedback loop may be made to vary non-linearly in response to charges in the magnitude of the output by including non-linear components in the differential amplifier 7. In the preferred embodiment, however, the gain of the feedback loop is varied by altering the conversion gain of the comparator 2, and this is effected by suitable shaping of the slope of the reference wave. For example, the wave may decay exponentially, or it may have a central portion of lesser slope than two adjacent portions. The way in which this sloping effects the desired gain control is described with reference to Fig. 2 (not shown).

Simulation of Controlled Sources Using Operational Amplifiers

Abstract: By using feedback around an infinite-gain controlled source four finite-gain controlled sources may be simulated. Cascading two of these yields other types of controlled sources. New configurations are obtained by compensating imperfect controlled sources and also by using a negative resistance in the feedback loop. By making use of the singular elements (nullator and norator), some alternative configurations are derived, raising interesting possibilities for network synthesis techniques which employ controlled sources. Finally, replacing infinite-gain controlled sources by operational amplifiers yields practical circuits.