Robert Boschgmbh

Wolfram Klemmer

Reinhard Kirschenstein

Harald Eschelbach

After sawtooth wave deflection signals are corrected in a summing circuit for position, magnitude, shape, they are keyed by a blanking circuit, within a blanking interval of the video signal, for briefly inserting a low-voltage reference potential. This is done before the corrected deflection signals are capacitively coupled to high voltage amplifying circuits supplying an electrostatic deflection plate of a camera tube. The high voltage amplifiers are equipped with a clamping circuit timed to clamp the high voltage output to a high voltage reference potential during substantially the same intervals in which the low voltage wave is keyed for insertion of the low voltage reference potential. The vertical deflection signals are keyed at low voltage and clamped at high voltage at the vertical scanning frequency. The horizontal deflection signals may be keyed and clamped either at the horizontal scanning frequency or, for saving of expense and equipment, at the vertical scanning frequency. It is particularly convenient for the clamping to take place at the beginning of the blanking interval of the video signal within which keying and clamping pulses are applied to the switching circuits involved in the keying and clamping.

Method of and apparatus for performing low-voltage correction of

A gamma stage of a television camera is automatically provided with regulation removing effect of variations in temperature, supply voltage and the like by means of two series of control pulses added to the video signal in blanking intervals of the signal before processing by the gamma stage. One series of pulses inserted in the horizontal blanking intervals, is compared after passing through the circuit with a reference value in a gated comparison amplifier providing a constant voltage output for the duration of a horizontal scanning interval, which is utilized to correct the d.c. offset of the video signal before it enters the gamma stage. Another set of control pulses inserted in the vertical blanking intervals is supplied to a gated comparison amplifier to produce an output signal that remains constant for a vertical scanning interval, which is used to provide a multiplicative correction to the output of the gamma stage for controlling the amplification of the circuit as a whole. The output of the multiplicative correction stage proceeds to the usual circuit for d.c. level clamping in the horizontal blanking intervals to produce the output available for further processing, which is also utilized by the comparison amplifiers for regulation purposes.

Method and circuit for nonlinear transmission-processing of a video

A video signal as it comes from a camera is inverted and clamped to an adjustable voltage for the black level and then proceeds at an amplified level to a differential amplifier that applies a signal to the gate of an N-channel FET. The voltage source provides a positive voltage through a load resistor and the drain-source path of the FET in series, while the drain electrodes is fed back through the differential amplifier in phase opposition to the incoming video, causing the drain current to vary in the same way as the video signal voltage. The applied voltage and the load resistor are such as to operate the FET in its saturation region, with the result that the gate voltage which is the voltage at the output of the differential amplifier, has the desired square root curve characteristic for correcting the gradation distortion of the picture tube. If a P-channel FET is used, the polarity of the voltage supply is reversed and the video is applied to the differential amplifier non-invertedly and clamped low rather than high. A potentiometer adjusts the clamping level to obtain the desired value of the gradation slope (gamma).

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Langen, Germany

Wolfram Klemmer