Sept. 29, 1959 L. DIETCH 2,906,814 SIGNAL OPERATED AUTOMATIC COLOR KILLER SYSTEM Filed April 28, l955 2. Sheets-Sheet l AAW22 a a2 aa’ a2/2 ass 122A 2 ASAf MaaZ AVA272M 77AAF42 4. A (So a 72.7 3.39 M269 22 66 (ol) (4) (C) -- - - - Hí2.É.-aws7 (a) A38 INVENTOR. Aawaz A7cay Aza y "(222a. A772AMMAY Sept. 29, 1959 L, DIETCH 2,906,814 SIGNAL OPERATED AUTOMATIC COLOR KILLER SYSTEM Filed April 28, 1955 2 Sheets-Sheet 2 |- 2,906,814 United States Patent Office Patented Sept. 29, 1959 1. 2 the phase of the sync bursts with the phase of the locally produced wave to derive a correction voltage for con trolling the frequency and phase of the oscillator which 2,906,814 produces the reference wave at the receiver. It is SIGNAL OPERATED AUTOMATIC COLOR desirable that synchronization of the receiver's color KILLERSYSTEM reference oscillator have been effected before the chro minance channel is activated, in order to prevent the Leonard Dietch, Haddonfield, N.J., assignor to Radio production of spurious color information pending such Corporation of America, a corporation of Delaware synchronization. Application April 28, 1955, Serial No. 504,503 O It is, therefore, a primary object of the present inven tion to provide new and improved automatic color chan 4 Claims. (C. 178-5.4) nel disabling means. Another object of the invention is the provision of automatic color channel disabling means, the operation The present invention relates to circuitry for automati 15 of which is correlated with the action of the receiver cally switching between two modes of operation and, color. Synchronizing circuitry. more particularly, to new and improved apparatus for In general, the present invention comprises a color automatically disabling the chrominance circuits of a killer circuit (i.e. color channel disabling means) capa color television receiver upon the reception of black and ble of operating upon a chrominance signal channel white television signals. 20 of a color television receiver in one of two fashions. In accordance with the standards promulgated by the That is, a killer circuit can provide a first output potential Federal Communications Commission on December 17, for biasing “off” the chrominance channel during recep 1953 for the transmission and reception of color tele tion of a black and white signal, for example, and a vision information, luminance or brightness information second output potential for rendering the chrominance regarding elemental areas of the televised image is trans 25 channel operative during the reception of a color tele mitted by way of amplitude-modulation of a carrier vision signal. In accordance with the invention, the wave, while information regarding the hue and satura action of the color killer circuit is correlated with that tion of the image areas is conveyed by phase-and of the color AFC arrangement of the receiver, so that amplitude-modulation of a color subcarrier wave whose the chrominance channel is maintained in a disabled con frequency is spaced a fixed amount from the video 30 dition until the AFC circuit has effectively synchronized carrier wave frequency. In order to detect the color the local color reference oscillator with the received sub information, it is necessary to provide some form of carrier wave. As will become apparent, the present demodulating apparatus, which, according to proposed invention affords the advantage of improved noise im systems, may comprise synchronous demodulating circuits munity. which serve to compare the incoming color Subcarrier 35 Additional objects and advantages of the present inven wave with the output wave of a color reference oscillator, tion will become apparent to those skilled in the art from thereby furnishing simultaneously information regarding a study of the following detailed description of the the phase and amplitude of the received subcarrier Wave. accompanying drawing, in which: In view of the importance of cooperation between trans Fig. 1 illustrates, by way of a block diagram, a color mitter and receiver in such a system, the color reference 40 television receiver embodying the present invention; oscillator must be synchronized with extreme accuracy Fig. 2 is a schematic circuit diagram illustrative of so that it produces a wave of the same frequency and the invention; and phase as that developed at the transmitter. Such Fig. 3 shows certain voltage waveforms to be described synchronism is accomplished by the periodic transmis in connection with the apparatus of Fig. 2. sion of a “burst" of signal wave equal to the frequency Referring to the drawing and, particularly, to Fig. 1 of the color subcarrier wave. A detailed description of 45 thereof, there is shown a block diagram of a color tele the use of bursts for color synchronization may be found vision receiver in connection with which the present in in an article entitled, "NTSC Color-TV Synchronizing vention may be employed. An incoming carrier wave, Signal” which appeared in the February 1952 issue of amplitude-modulated by the composite color television Electronics, published by McGraw-Hill Publishing Com signal including luminance and chrominance components pany, Inc. The burst of subcarrier wave frequency is 50 and color sync bursts, is intercepted by an antenna 10 superimposed on the “back porch” of each horizontal and is applied to a tuner section 12 which includes radio blanking pulse. frequency amplification stages, a mixer or first detector In order that the receiving apparatus designed for wherein the modulated carrier wave is translated in color television image reproduction may also serve to frequency to an intermediate frequency and an intermedi reproduce high quality black and white pictures when 55 ate frequency amplifier. The amplified IF signals are receiving ordinary monochrome television signals, the applied via a lead 14 to a second or video detector 16 receiver may be arranged in such manner as to arrest or which provides at its output terminal 18 the detected disable the color demodulating circuits when monochrome composite color television signal. television signals are being received. Such disabling The composite signal thus recovered from the video of the chrominance channels (i.e., the color demodulating 60 detector 16 is amplified in a broad band video amplifier channel) of a color receiver during the reception of stage 20 and is applied simultaneously to several channels black and white image signals has been found necessary of the receiver, as follows: in order to prevent spurious color beat patterns from The signal is applied via a lead 22 to the deflection and appearing in the monochrome reproduction as a result high voltage circuits 24 comprising suitable means for gen of random demodulation of high frequency picture and 65 erating scanning sawtooth current waves of television line noise components appearing in the color channel. As and field frequencies for application to the electromagnetic mentioned, the color synchronizing bursts are employed deflection yoke 26. In a well-known manner, the fly at the receiver in synchronizing the locally produced back voltage pulses produced in the horizontal deflection reference subcarrier wave with the transmitter subcarrier circuit are rectified to produce a high, unidirectional pos wave. This synchronization may be brought about 70 itive potential for application via a lead 28 to the final through the agency of a color AFC circuit for comparing anode of the tricolor kinescope 30. Also produced by the 2,906,814 3 4 deflection circuits 24 and provided at the terminal 32 are subsidiary. It is also to be noted that, as described, the burst gating pulses derived from the horizontal flyback apparatus of Fig. 1 is capable of reproducing either color pulses and having a duration corresponding Substantially television images or monochrome images, depending upon to that of the color synchronizing burst referred to above. the presence or absence of a phase- and amplitude-modul The gating pulses may be produced, for example, through lated color subcarrier wave in the received signal. As the agency of a flyback winding on the horizontal deflec has been stated, color television signals of the standard tion output and high voltage transformer forming a part variety include the color synchronizing bursts, which of the horizontal deflection circuit. bursts are absent from a black and white signal. In order The luminance signal component of a composite re that the color signal processing channel including the ceived television signal is applied from the video amplifier chrominance amplifier 42 and demodulator circuitry 38 20 to a luminance amplifier and delay circuit represented may be operative for the detection of color information by the block 34 which provides at its output terminal 36 during the reception of a color television signal but in the luminance signal Ey for application to the demodula operative when monochrome television signals are being tor and matrix circuits 38. received, the additional apparatus of Fig. 1 is provided, in The composite color television signal is also applied 5 accordance with the present invention. The block 72 from the video amplifier via a lead 40 to a chrominance bearing the legend "color killer circuit' receives signals via bandpass amplifier 42 which serves to separate the sub the leads 74 and 76 from the phase detector 60 and phase carrier wave or chrominance signal information from the shifting circuit 66, respectively, and provides at its output composite signal and to amplify the same. The amplified lead 78, for application to the chrominance bandpassam chrominance signal is, in turn, applied via a lead 44 to 20 plifier 42, a control voltage capable of selectively render the demodulator and matrix circuits 38 which may be ing the amplifier 42 operative or inoperative. Such ac understood as performing a process of synchronous de tion of the color killer circuit 72 is based upon reception modulation upon the chrominance signal to derive there- .