Rca Inc.

Lucas J Bazin

Dennis Michael Schneider

Joseph F Hacke

Gary Ray Peterson

Donald C Herrmann

Arthur J Banks

Charles L Olson

A circuit including emitter-coupled transistors improves the symmetry of an applied square wave. A limiter in the collector circuit limits the paraphase output voltage excursion. Changes in energizing voltage affect the current in the limiter and cause incremental changes in the output duty cycle. A compensator includes a voltage divider coupled between the output terminals for producing a control voltage related to the output signal amplitude. The control voltage controls a current source coupled to joined emitters for creating an offsetting current through the limiter.

Square-wave symmetry corrector

A balanced modulator or mixer is used for modulating components of a chrominance signal onto a subcarrier to generate double-sideband suppressed-carrier amplitude-modulated signals. The video component is applied to a phase splitter which produces two antiphase baseband video signals, which in turn are applied to modulator switches driven in antiphase at the carrier rate for producing the DSB SC signal at a common output terminal. For reducing residual carrier output resulting from unbalance of the video during black level, a sample-and-hold circuit is coupled to each output of the phase splitter and is gated during black level. A differential amplifier compares the sampled signals and reduces the unbalance in a feedback manner to eliminate residual subcarrier during black level.

Balanced modulator with feedback stabilization of carrier balance

A feedback amplifier is configured as a contrast compressor for video signals including a reference blanking level. A feedback resistance is divided into two resistors coupled at a juncture. Contrast compression is accomplished by a diode coupled to the juncture and to a voltage source which may be adjusted to vary the point of onset of compression. The diode current perturbs the operating point of the amplifier, thereby producing a condition in which the blanking level at the output is other than zero volts. This is undesirable as it may affect following circuits adversely or require further setup. A clamp is coupled to the inverting input terminal for offsetting the perturbation of the amplifier operating point caused by the diode current.

Adjustable contrast compressor

A synchronizing apparatus for compensating for cable length changes between a remote color television camera and a local control point is described. The color camera is of the type adapted to receive a 'gen-lock' type reference signal for synchronization. The apparatus is responsive to the 'gen-lock' signal and the signal from the television camera for generating a 'gen-lock' type signal phase advanced to compensate for cable delays.

Synchronizing apparatus for remote television apparatus

A remotely controlled chroma key soft edger is described for use with an analog switcher. The keying signal is a low passed filtered and differentially summed with substantially an unfiltered keying signal and the resultant high frequency components are summed with the low pass filtered signal. The gain of the peaking signal is remotely controlled to adjust the summed rise time of the keying signal.

Low-pass filter with remotely controllable rise time

A remotely controlled chroma keyer is provided which is responsive to the red, green and blue signals from a video source such as a color camera for providing color difference signals. A signal processing system using quadrant multipliers is used for summing and differencing these color difference signals which when applied to a non-additive mixer select a particular color. The color selection is determined by control voltages applied to the multipliers.

Chroma keying selector system

A cable equalizer is provided for automatically compensating a signal for cable attenuation as the length of the cable is varied. The circuit detects changes in a reference signal that is inserted in the signal being transmitted over the cable. Any deviation of the reference signal from its normal state at the receiving end of the cable causes the addition of a correction signal to the signal being transmitted so as to compensate the signal for the cable attenuation.

Automatic cable equalizer circuit

A plurality of comparators are used to compare first, second, and third input signals against a first and second predetermined signal level threshold. The outputs of the comparators are combined to ascertain the difference in signal amplitude between the first, second, and third input signals with respect to the first and second predetermined signal thresholds. If the amplitude deviation of the first, second, and third signals are within the threshold limits, a control signal adjusts the characteristics of the first and second signal channels to match the amplitude of the first and second signals to the amplitude of the third signal to make the three input signals equal. If the first, second, and third input signal deviation is without the threshold limits, the input signals are assumed correct, and no adjustment is made.

Signal comparator circuit

A sync regenerator is provided which regenerates synchronizing information signals having a varying amplitude and width by comparing the sync signals in a comparator circuit to which a source of reference potential is applied. The comparator output signal of fixed amplitude is pulse width detected and the value of the detector output voltage is coupled by a feedback circuit to the reference potential source to vary the reference potential so as to maintain the width of the comparator output signal constant. The regenerated sync output signal is of constant amplitude and constant width.

Constant pulse width sync regenerator

A plurality of comparators are used to compare the red, blue and green color signals of a color television camera against a first and second predetermined signal level threshold corresponding to selected values of grey scale. The outputs of the comparators are combined to ascertain the difference in signal amplitude between the red, blue and green signals with respect to the first and second predetermined signal thresholds which represent grey. If the amplitude deviation of the red, blue and green color signals is within the threshold limits, a control signal adjusts the gamma characteristics of the blue and red color channels to match the amplitude of the red and blue color signals to the amplitude of the green color signal to correct to grey. If the red, blue and green color signal deviation is without the threshold limits, the color signal is assumed correct and no adjustment is made. The system provides automatic and continuous correction of gamma characteristics of the video signals generated by the television camera during the telecasting of an actual program source.

Apparatus for automatic gamma control of television color signals

A video blanking circuit is provided which inserts a system blanking interval signal having controlled leading and trailing edges into a video signal. The blanking signal is combined with a clamped video signal in a first non-additive mixer which also provides a white clip level. The output of the first non-additive mixer is further coupled to a second non-additive mixer in which black level excursions are clipped so as to provide an output video signal having a proper system blanking interval into which synchronizing information may be added to complete the composite video waveform.

Video blanking circuit

A push-pull common emitter deflection output stage energized by a relatively low direct voltage includes zener diode drive coupling to its input circuit for reducing crossover distortion. A diode in series with a deflection winding disconnects the output stage from the winding during a portion of the retrace interval to allow the retrace pulse voltage to rise to a relatively high direct voltage supplied through a switched transistor only during the retrace interval to reduce power dissipation in the output stage. Current feedback from the deflection winding to a driver stage during trace and retrace intervals accurately determines the retrace duration.

High efficiency deflection circuit

An electronic signal mixer is provided for combining first and second signals by additively (or differentially) combining the first and second signals to provide a first output signal. The first and second signals are further combined in a multiplier circuit to provide an output signal which is a differential (or additive) combination of the first and second signals multiplied by a coefficient determined by a control voltage applied to the multiplier. The first combined signal and the product output of the multiplier are further combined to provide a resultant signal comprised of any proportionality of the first and second signals in accordance with the value of the control voltage.

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Vincentown, NJ, United States of America

Lucas J Bazin