Zenith Radio Corporation

Zenith Electronics Corporation

George J Tzakis

Christopher M Engel

Gopal K Srivastava

Fred D Johnson

Michael D Flasza

Daniel L Reneau

Stan Bart

Alain H d'Hautecourt

David H Meehan

Richard Avicola

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 integratable amplifier is disclosed for developing a high level output signal with reduced power dissipation. The amplifier includes a first circuit (108, 110) which responds to an input signal for developing first and second signal currents whose amplitudes increase and decrease, respectively, in response to an input signal transition of a given direction. A second circuit (32a) receives the first signal current for establishing a third signal current which mirrors the first signal current. The second and third signal currents are received by a third circuit (70a) for conversion thereof to an amplified output signal. To stabilize the gain of the amplifier, a negative feedback path (50a) is coupled between the input signal and the output signal.

Amplifier having reduced power dissipation and improved slew rate

A circuit is disclosed for establishing proper video output voltages in a color television receiver prior to setting the receiver's G2 voltage. In the preferred embodiment, the circuit includes three emitter follower stages, each coupled to the output of a video amplifier. The collectors of the emitter follower stages are coupled to a supply voltage through a common resistance. A two position switch is connected across the common resistance such that, during normal receiver operation, closure of the switch shunts the common resistance. When G2 set-up is to be effected, the switch is opened so that a predetermined voltage is dropped across the common resistance and the three emitter follower stages have similar, predetermined D.C. output voltages.

G2 Set-up circuit for a television receiver

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 television receiver includes an interface circuit enabling the production of on-screen displays of alpha-numeric type information in a selected color. The interface circuit is responsive to a blanking signal for reducing the red, green and blue video signals developed in response to a received NTSC color television signal below the blanking level of the television receiver. A digital signal representing selected alpha-numeric type information is coupled from a character generator to the interface circuit for increasing the potential at one or more of the electron guns of the receiver for producing a corresponding on-screen display in a selected color.

On screen color display

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 ramp generator is described for developing a ramp voltage for use in vertically deflecting the electron beam or beams of a television receiver. The ramp generator receives a vertical rate pulse developed by the receiver for developing a charging current during the occurrence of the vertical rate pulse. A discharging current is also generated, and both currents are applied to a capacitor for developing a ramp voltage which increases and then decreases in amplitude. A clamp circuit in the generator is enabled when the vertical pulse is received for clamping the ramp voltage on the capacitor to a predetermined peak voltage via low impedance path such that unwanted voltage components are substantially eliminated from the ramp voltage during the clamping action.

Vertical ramp generator for a television receiver

A D.C. tint control is described for use in a color television receiver. The tint control receives a pair of 3.8 megahertz currents which are preferably in phase quadrature with each other, and a D.C. control voltage whose value is variable by a viewer to change the tint of reproduced color images. The ting control includes a current-steering circuit responsive to the value of the control voltage for steering a controlled portion of each quadrature current to a load, the latter of which is coupled to a color demodulator. The resultant voltage across the load is a 3.58 megahertz signal whose phase is variable over a reproducible range of about ninety degrees.

D.C. Tint control

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 full-wave rectifier is disclosed for rectifying low level A.C. input signals. In the disclosed embodiment, the rectifier includes first and second differential amplifiers, each constructed of a pair of transistors. One transistor in each pair of transistors has a D.C. operating point offset from that of the other transistor so that the offset transistor conducts only on an excursion of a given polarity of a received A.C. input signal. Both output currents of the offset transistors are coupled to a load, across which a fully-rectified version of the A.C. input signal is developed.

Full-wave rectifier

A color television receiver chrominance channel has first and second chrominance amplifiers supplying chrominance demodulators. An automatic chrominance control (ACC) is operative upon the first chrominance amplifier to maintain a substantially constant signal level. An automatic chrominance level control including a symmetrical amplitude limiter having a nonlinear gain characteristic for chrominance signals above a predetermined amplitude threshold is interposed between the first and second chrominance amplifiers.

Automatic chroma level system

A television receiver includes a conventional tri-color cathode ray tube display system having horizontal and vertical scansion systems. Conventional signal receiving and processing circuitry recovers picture, sound and scansion synchronizing information. A high voltage shutdown circuit is responsive to excesses of either high voltage or CRT beam current. The former being detected by a resistance divider coupled between high voltage and ground while the latter is sensed by a resistor placed in series with the secondary winding of the horizontal deflection transformer. A PNP, NPN transistor pair configured to form a switch analogous to a silicon controlled rectifier responds to detected excesses of beam current or high voltage and loads down the operating supply to the horizontal scansion oscillator to terminate high voltage generation. The transistor pair accommodates a degenerating network to reject false triggering.

High voltage shutdown circuit responsive to excessive beam current and

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

Glenview, IL, United States of America

George J Tzakis