A variable speed drive (VSD) having a rectifier, an inverter, an inverter modulator, an inverter controller, and a control loop, for controlling a motor load, wherein the control loop reduces an amount of power transferred to the inverter during a voltage sag. The control loop may include a reference generator, a filter, a regulator, and a ride-through corrective algorithm. A method for controlling a VSD to improve voltage sag ride-through by monitoring a voltage applied to the VSD, generating a control signal representative of losses in a motor load when a voltage sag is detected in the voltage applied to the VSD and applying less power to the load of the inverter.

Control loop and method for variable speed drive ride-through capability improvement

A signal substitution system is employed in audio processing circuitry to compensate for impulse noise and signal dropouts. Stored or delayed audio signal is substituted in the IF portion of the receiver circuitry ahead of the IF filters thereby precluding the noise impulses from exciting the filters into a ringing mode and significantly broadening what are otherwise very narrow signal disturbances. To insure that the substitution signal is in relative phase coherence with the substituted signal, the substitution signal is delayed an integral number, N, of cycles of the audio carrier. The number N is chosen to be small, resulting in the change in the modulating signal corresponding to the stored portion of the carrier being small. The affect on the baseband signal is that during instances where defects occurred the signal appears to have been sampled and held, but the duration is so short that they are not audibly distinguishable.

Noise reduction circuitry for audio signals

Brightness control apparatus for a video signal image reproducing system including a video signal processing channel, a source of reference voltage for establishing a desired level of image brightness, and a keyed comparator circuit. The comparator forms a closed control loop with the signal processing channel, and is keyed during periodic blanking intervals of the video signal to sense the magnitude of the reference voltage and a brightness representative blanking level of the video signal which may vary undesirably. The comparator provides an output control signal indicative of a voltage difference between the reference voltage and the blanking level. The control voltage is applied to the signal channel for translating the blanking level in a direction to minimize the voltage difference, so that a desired relationship between the reference voltage and the blanking level is preserved.

Brightness control circuit employing a closed control loop

A video signal processing circuit is disclosed which has a wave-forming circuit for setting the level of an input video signal to a predetermined first DC level, which is higher than the pedestal level of the input video signal, at least during the blanking period of the input video signal, and producing a wave-formed signal; a peak-hold circuit for detecting and holding the level of the darkest peak of the wave-formed signal and producing a peak-hold output signal; and a black level control circuit controlled by the peak-hold output signal for controlling the DC level of the input video signal so that the darkest level of the input video signal coincides with a predetermined second DC level

Video signal processing circuit

A system for calibration and closed loop feedback control of image signals from charge coupled imaging devices (CCDs) (16). During periodic calibration, sampling the output of dark reference cells on a CCD nets an initial D.C. restoration voltage (black) level. Next, a black reference strip is scanned and, an offset value is determined and an offset voltage is added to the D.C. restoration (black) level. During each scan line of regular scanning, dark cells are sampled and produce a voltage that is modified by the offset voltage that was determined during calibration.

Automatic d.c. offset control for image scanners.

A DC level control circuit wherein the DC level of an input signal is compared to a reference level and a DC bias potential is varied in accordance with said comparison, the varied bias potential being fed back to correspondingly vary the DC level input signal.

DC level control circuit

In an automatic phase control circuit having a predetermined lock-in range wherein the oscillating signal produced by the adjustable oscillator of the automatic phase control circuit is used in combination with an input signal to derive a signal whose phase is compared to a reference signal, the phase difference between the derived signal and the reference signal being used as a phase control signal for the oscillator so as to minimize this phase difference and thus lock the phase of the derived signal to that of the reference signal, a method of adjusting the oscillator in the event that the phase relation between the oscillating signal and the input signal is outside the lock-in range. During recurrent intervals, which vary with time base errors in the input signal, the number of cycles of the oscillating signal is counted. The count is examined to determine whether it is within a predetermind range of a predetermined count, and if outside this range, the oscillating frequency of the oscillator is adjusted in a direction to return the count to within this predetermined range. In a preferred embodiment, this automatic phase control circuit is used to eliminate time-base errors in at least the chrominance signal of a composite color video signal. In such an embodiment, the adjustable oscillator is used in a frequency-converter for converting the frequency of at least the chrominance signal from an input frequency to a different frequency, and it is the phase of the frequency-converted chrominance signal which is compared to the reference signal.

Time-base error correction

Apparatus for eliminating time base errors from a carrier-modulated information signal, such as a color video signal which is reproduced from a record medium. A circuit including a variable oscillator generates a carrier signal of controllable frequency and phase. An automatic frequency control circuit detects the time base frequency error in the carrier-modulated information signal and produces a frequency error signal proportional to the detected frequency error. An automatic phase control circuit detects a time base phase error in the carrier-modulated information signal and produces a phase error signal proportional to the detected phase error. A switching circuit selectively supplies either the frequency error signal or the phase error signal as a control signal to the variable oscillator so as to correspondingly control the frequency and phase of the generated carrier signal in a manner to eliminate such frequency and phase errors, the frequency and phase error signals being supplied to the variable oscillator during selected, mutually exclusive intervals. A frequency converter is provided with the controlled carrier signal and with the information signal so as to convert the carrier of the information signal with the generated, controlled carrier such that the frequency-converted information signal has a carrier of substantially constant frequency and phase.

Apparatus for eliminating time base errors from an information signal

In an apparatus for processing reproduced color video signals composed of a frequency-modulated luminance component and a frequency-converted chrominance component having its carrier frequency substantially below a standard frequency therefor; there are provided a drop-out compensating circuit responsive to a drop-out in the luminance component for inserting, in the interval of such drop-out, an earlier occurring portion of the luminance component, a frequency-converter receiving the chrominance component and a frequency-reconverting signal for restoring the carrier frequency to the standard frequency therefor, an automatic frequency control circuit (AFC) responsive to horizontal synchronizing signals separated from the luminance component after the drop-out compensation thereof so as to regulate the frequency-reconverting signal in the sense for removing time base errors from the reproduced color video signals, and a circuit which is responsive to a drop-out in the luminance component for maintaining the frequency of the frequency-reconverting signal at a previously determined value during the drop-out so that the automatic frequency control operation will not be adversely affected by the drop-out compensation.

Drop-out responsive color video reproducing apparatus

PURPOSE: To make a circuit suitable to IC implementation by realizing a digitally- constituted part to be added to a circuit which controls the period of an APC circuit by supplying a voltage to the variable frequency oscillator of the APC circuit. CONSTITUTION: A burst signal, extracted from the chrominance signal of a color video signal, is phase-compared 26 with a reference subcarrier signal and variable frequency oscillator 23 is controlled by the comparison error voltage to generate the frequency converting signal for the chrominance signal. The oscillation signal of this variable frequency oscillator 23 is extracted periodically for a fixed time and counted 44 and it is discriminated by this counting output whether the oscillation frequency of oscillator 23 is within a certain range or not; if it is without the range, the comparison error voltage is supplied to oscillator 23 after being applied with a voltage equivalent to the different direction COPYRIGHT: (C)1979,JPO&Japio

Yasunobu Kuniyoshi

Papers

DC level control circuit

Time-base error correction

Apparatus for eliminating time base errors from an information signal

Drop-out responsive color video reproducing apparatus

Processing circuit for color video signal