Zenith Radio Corporation

Zenith Electronics Corporation

Christopher M Engel

George J Tzakis

Gopal K Srivastava

Daniel L Reneau

Khosro M Rabii

A luminance signal transient improver and non-linear peaking arrangement processes a digital luminance signal by generating a first difference signal and a second difference signal and developing therefrom a threshold control signal, a high frequency peaking signal and a low frequency peaking signal. The high frequency peaking signal consists of the second difference signal as modified by a high pass filter and the threshold control signal consists of the second difference signal as modified by a threshold circuit. The first difference signal is passed through an absolute value circuit and a low frequency emphasis circuit and modified by the threshold control signal and added to the high frequency peaking signal. The combined result is subjected to non-linear filtering and added to the luminance signal to form a horizontally processed luminance signal. A comb filter develops a vertical detail component representing differences between successive lines of luminance and combines the vertical detail component with the luminance signal to form a vertically processed luminance signal which is combined with the horizontally processed luminance signal to develop a fully processed luminance signal.

Digital luminance signal transient improver and peaker

A black expander circuit for a digital video signal includes a pair of moving average filters, one sampling pixels on a line basis and another sampling the pixel samples on a field basis to develop a moving digital average. The moving digital average is added to a constant to form a breakpoint value and supplied to a comparator along with the digital video signal. The output of the comparator controls a mutiplexer. The digital video signal is multiplied by a factor, algebraically summed with the breakpoint value and supplied as one input to the multiplexer with the digital video signal being supplied as the other input. The output of the multiplexer comprises a digital video signal that has portions below the breakpoint value expanded.

Digital video black expander

A digital auto tracking system compares sampled operating data from a CRT with corresponding reference data and develops an error signal therefrom. The error signal is truncated to produce a desensitized three bit error signal. Three AND gates each have one input supplied with the three error bits, respectively, and three programmable velocity control bits are supplied to the other inputs by a microprocessor. A demultiplexer has a plurality of input taps that are coupled together so as to provide a minimum of zero and a maximum of seven clock pulses depending upon the outputs of the AND gates. The clock pulses sequence up/down counters in accordance with the derived error signal. The speed or velocity of change in response to the error signal is determined by the velocity control bits which may be microprocessor controlled for optimum block and white tracking of the particular cathode ray tube.

Velocity controlled CRT auto tracking system

A luminance peaking circuit includes a common and differential mode amplifier comprising a first differentially coupled pair of transistors coupled to a current source and functioning in a differential mode and a second differentially coupled pair of transistors functioning in a common mode. The bases of the second pair of transistors are connected together and to the base of one of the first pair of transistors. The inputs to the amplifier comprise a common mode signal and a differential mode signal and the outputs are matrixed to produce common mode signal components with opposite polarity differential mode components. The amplifier is characterized by a differential mode gain that is independent of common mode signal level and a common mode gain that is independent of differential signal level.

Non-linear peaking system

An automatic beam current limiting circuit for a color television receiver comprises means for individually monitoring the three cathode currents developed in response to the green, blue and red video drive signals. The video processing unit of the receiver is automatically adjusted in response to any one of the cathode currents exceeding a predetermined level for reducing the video drive signals to limit the excessive cathode current to the predetermined level. As a result, the individual cathode currents are limited to the predetermined level while the combined cathode currents are allowed to substantially exceed this level.

Automatic beam current limiter

A VIR Correction system is disclosed for use in a system such as a color television receiver. Television signals of the type under consideration include a plurality of video lines, each line having a standard color burst and video chrominance. On line 19 of each television field, a VIR signal is transmitted which includes a VIR color burst and a VIR chrominance reference. The correction system includes an amplitude comparator for sensing the difference in amplitude between the VIR color burst and the VIR chrominance reference, and for developing an amplitude error signal indicative of the sensed difference. A phase comparator develops a phase error signal on sensing a phase difference between the VIR color burst and the VIR chrominance reference. A phase controller receives at least the standard color burst portion of the television signal and responds to the phase error signal for correcting the phase of the standard color burst. A gain controller receives at least the video chrominance portion of the television signal and responds to the amplitude error signal for correcting the amplitude of the video chrominance.

VIR Correction system

A DC coupling reduction circuit for use in a television receiver having a DC restoration circuit comprises means for developing a dynamic adjustment signal by attenuating a video signal by a selected percentage, inverting the attenuated signal and low pass filtering the attenuated and inverted signal. The dynamic adjustment signal is combined with a viewer selected direct current black level reference signal to produce a combined signal which is coupled to the black clamp level determining input of the DC restoration circuit whereby the black level of the video signal is clamped at a potential which is a function of the video signal. Preferably, the cut-off point of the cathode ray tube of the television receiver is set at a level between the levels of the combined signals produced in response to a video signal representing a white image and a video signal representing a black image.

One-chip chroma/luma IC: D.C. coupling reduction circuit

A tint control circuit is described for use in a color television receiver. The circuit generates four currents having substantially equal D.C. components, and having respective 3.58 MH.sub.z subcarrier components of four different quadrature phases. The phase of each such current is preferably variable over a range of .+-.45 degrees. In a preferred embodiment, the four currents are coupled to a matrixing network for developing a pair of subcarrier output voltages whose phases differ by more than 90 degrees and whose D.C. components are substantially equal. As the phases of the four currents are varied, the phases of the subcarrier output voltages vary accordingly, but maintain their phase relationship to each other.

Tint control

A color demodulation and matrixing system is disclosed for use in a color television receiver. The matrixing portion of the system receives R-Y and B-Y color-difference signals which may be developed by conventional demodulators. Each color-difference signal is converted to a pair of currents of opposing polarities which are coupled to a current node, and a load is coupled to the node for developing a G-Y voltage across the load. The demodulation portion of the system receives the R-Y and B-Y color-difference signals, converts each of them to currents of opposing polarities, and applies them to loads in push-pull fashion to develop R-Y and B-Y output voltages.

Color demodulation and matrixing system

A dynamic enabling network is described for turning off and on a color correction network in a color television receiver. The enabling network receives and combines selected color-difference signals which are superimposed on a D.C. bias level so as to generate a first control signal whose amplitude is near a maximum when the color-difference signals are representative of fleshtone hues. A second control signal, also derived from the selected color-difference signals, is a D.C. signal whose amplitude is a function of the D.C. bias level associated with the selected color-difference signals. Both control signals are applied to a comparator for turning on the color correction circuit only when the difference in amplitude between the two control signals is indicative of hues within a selected range of fleshtones.

Dynamic enabling network for a color correction circuit

A control network and method for a color television receiver is described for enabling and disabling the limiting action of a conventional ACL (Automatic Color Limiter) circuit, for varying the threshold at which a color killer circuit inhibits reproduction of color images, or for effecting both functions simultaneously. In the preferred embodiment, the control network includes a two-position switch by which the viewer can either increase or decrease the value of a reference signal to thereby control the degree of amplification of a received color signal. An amplifier is responsive to a reduction in the amplitude of the reference signal for substantially disabling the limiting action of the ACL circuit and for causing the color killer to inhibit reproduction of color images when a relatively small amplitude color signal is received. When operation of the switch increases the amplitude of the reference signal, the amplifier responds by enabling the limiting action of the ACL circuit and causing the color killer to inhibit reproduction of color images when a relatively larger amplitude color signal is received.

Control for color killer and automatic color limiter

An integrated injection and demodulation system is described for developing three color-difference signals in a color television receiver. To employ three separate demodulators, one for each color-difference signal, on a single integrated circuit chip without increasing the number of externally generated oscillator injection signals required, the system utilizes two such injection signals whose phases and amplitudes are such that their vector differences are employed to demodulate along one axis, and one of the injection signals is used to demodulate along a second axis. In addition, a fraction of one of the injected signals is developed inside the chip and vectorily subtracted from the other injection signal for demodulation by the resultant signal along the third color-difference axis.

I.C. chroma injection and demodulation system

A buffer amplifier is described for use in an integrated circuit in which a siganl from a processing circuit is coupled by the buffer amplifier to an output pin on the integrated circuit. The buffer amplifier includes a pair of transistors, the first of which receives the output of the processing circuit and is preferably arranged in an emitter-follower configuration. A resistor internal to the integrated circuit is coupled between ground and the emitter of the first transistor. The second transistor, preferably a vertical PNP type transistor, is arranged in a circuit configuration to couple the output of the first transistor to the output pin and to sink any current flowing to the output pin from a circuit driven by the buffer amplifier.

Buffer amplifier

A regulation system includes a series regulator comprising a Darlington arrangement of transistors, a Zener diode shunt regulator, and a current sensor for controlling the series regulator in accordance with the Zener current. The regulation system is on an integrated circuit with the exception of the voltage dropping resistors.

Combination voltage regulating system

A color television receiver includes conventional circuitry for processing and detecting a received color television signal. Three chrominance-luminance matrices combine detected color difference and luminance signals forming color red, blue and green video signals. Emitter follower coupling stages apply the color video signals individually to each of three output amplifiers which in turn drive the cathode electrodes of a unitized gun CRT. Potentiometers couple the emitter electrodes of the output amplifiers to a source of operating potential providing a simultaneous signal gain and DC output voltage adjustment for each amplifier during CRT color temperature setup. A voltage divider controls the voltage applied to the common screen grid electrode of the CRT providing a master setup adjustment.

Growing community of inventors

Arlington Heights, IL, United States of America

Christopher M Engel