APPLICATION OF RICHMAN, Patent Appeal No. 8281.

• Decision Date: 07 May 1970
• Docket Number: Patent Appeal No. 8281.
• Citation: 424 F.2d 1388
• Parties: Application of Donald RICHMAN.
• Court: U.S. Court of Customs and Patent Appeals (CCPA)

424 F.2d 1388 (1970)

Application of Donald RICHMAN.

Patent Appeal No. 8281.

United States Court of Customs and Patent Appeals.

May 7, 1970.

Laurence B. Dodds, Great Neck, N. Y., attorney of record, for appellant; Jesse C. Bowyer, Washington, D. C., of counsel.

Joseph Schimmel, Washington, D. C., for the Commissioner of Patents; Jere W. Sears, Washington, D. C., of counsel.

Before RICH, Acting Chief Judge, ALMOND, BALDWIN, and LANE, Judges and FORD, Judge, United States Customs Court, sitting by designation.

RICH, Acting Chief Judge.

This appeal is from the decision of the Patent Office Board of Appeals affirming the rejection of claims 1-3, 11, and 12 of appellant's reissue application serial No. 299,141, filed July 26, 1963,¹ for reissue of his patent No. 2,933,558, granted April 19, 1960, on an application filed December 23, 1957,² for "Noise-Immune Synchronizing-Signal Separator for Television Receivers."

Three issues are raised. One is whether the appealed application is defective for lack of a reissue oath complying with the requirements of 35 U.S.C. § 251. A second issue pertains to the rejection of claims 11 and 12 "as involving new matter." The third issue is whether claims 1-3, 11, and 12 are unpatentable over the prior art.

The Invention

The invention relates to a circuit for deriving synchronizing pulses from the composite signal received by a television receiver without the introduction of false pulses resulting from random electrical noise which may be present in the signal.

As background, the television video (picture) signal is produced in a television camera tube which employs an electron scanning-beam to read off variations of voltage amplitude corresponding to the portions of a picture image focused on a photo-sensitive surface. The image is reproduced in a receiver picture tube by causing another electron beam which is modulated and deflected in synchronism with the beam in the camera tube to impinge on a photophosphorescent surface.

The scanning is accomplished by moving the beam repeatedly in parallel lines extending from what we will term left to right across the scanned surface with the first line at the top of the surface and each succeeding line vertically displaced below the preceding line until a "field" covering the vertical extent of the surface has been traversed. The beam is returned to the left at an increased speed following completion of each line to begin the next line and is returned to the top at a similarly increased speed at the end of each field to position it for the start of the succeeding field.

The transmitted video signal includes the modulated picture signals representing light variations in the successive lines, blanking pulses between the modulated signals for blanking out the beam between succeeding lines, and line and field synchronizing pulses for establishing the time for starting each line and each field, respectively. In standard United States practice, the picture signal is negatively modulated, which means that decreases in its amplitude correspond to increases in light or whiteness of the image, the blanking pulses are at a greater amplitude corresponding to black in the picture, and the synchronizing pulses are superimposed on the blanking pulses to extend further into the black region.

In the receiver, a composite video signal having the above described components is derived from a modulated carrier signal received at the antenna. The derived signal is so imposed on the beam-modulated components of the picture tube that the beam increases in intensity with decreases in the modulated signal and is blanked out during the blanking pulses and the synchronizing pulses. In order to coordinate the scanning of the lines and fields by the electron beam of the receiver tube with the camera beam, the receiver is provided with a line-scanning generator and a field-scanning generator which are held in proper synchronism by application thereto of the line-scanning pulses and field-scanning pulses respectively. The present invention deals with the separation of the synchronizing pulses from the composite signal. That separation is attained in conjunction with production of an AGC (automatic gain control) signal for application to early stages of the receiver, including the radio-frequency and intermediate-frequency amplifiers, to adjust their gain or amplification and thus automatically maintain the strength of the composite video signal substantially uniform despite variations in the strength of the received signal due to fading and the like.

In appellant's receiver, the composite video signal is applied to the grid of an AGC rectifier tube of triode form. That tube is connected so as to develop in its anode circuit a negative bias voltage which is proportional to the strength of the applied signal and that bias voltage is applied to control the gain of the circuits in the receiver ahead of the output of the composite video signal itself. The AGC tube also develops in its cathode circuit a bias voltage of the same general character as the anode voltage but of opposite, or positive, polarity. That voltage varies in strength proportionally to the strength of the synchronizing signals and, consequently, to the strength of the signal picked up by the receiver antenna.

Concurrently, the composite video signal, with the synchronizing signals of positive polarity, is applied to the control grid of a synchronizing-signal separator tube through a high value resistor so that positive values of that signal tend to make this tube conductive. However, the aforementioned positive bias developed in the AGC tube circuit is applied to the cathode of the synchronizing-signal separator tube through a resistor network in the circuit of that cathode and the effect of that bias is to tend to make the separator tube nonconductive. The result is that the latter tube becomes conductive only during the peaks of the synchronizing signal. When the tube becomes conductive, it develops a synchronizing pulse in its output circuit and the pulses so developed are applied through a suitable circuit for application to the scanning generators.

Since the bias developed across the network in the cathode of the AGC tube is derived from the synchronizing signal, and varies dynamically with its magnitude, that bias and the synchronizing signal rise and fall together. Consequently, the separator tube conducts only on the peaks of the synchronizing signal whether it is weak or strong.

Up to this point, we have not considered the fact that the received composite video signal is frequently accompanied by strong electrical disturbances termed "noise," which often are of a form similar to, but stronger than, the synchronizing pulses themselves. These noise pulses occur at random times and, if mistaken for synchronizing pulses by the synchronizing circuits of the receiver, would cause the receiver to drop out of synchronism and possibly distort the image on the picture tube beyond recognition.

Appellant's receiver is provided with a circuit for eliminating that effect of noise signals. The circuit includes a diode connected between the input circuit to the grid of the synchronizing-signal separator tube and the cathode of that tube. It is biased against conduction by the bias potential produced across the resistor network in the cathode circuit of the separator tube. However, the characteristics and connection of the triode in the circuit are such that a stronger signal is required to make the diode conductive than is required to make the synchronizing signal separator tube conductive. That is, the diode becomes conductive only when the composite signal impressed on the grid circuit of the separator tube includes signals, such as noise, which are greater in amplitude than the synchronizing pulses. Since the diode is connected at one terminal to the cathode of the separator tube and thus is subjected like that tube to a bias potential which rises and falls with variations in the strength of the received signal as measured by the amplitude of the synchronizing signal, the threshold or signal level at which the diode becomes conductive likewise varies dynamically with the strength of the received signal while remaining above the amplitude of the synchronizing signals.

When a noise signal of high amplitude occurs in the composite video signal, the diode becomes conductive and passes a current through the resistors in the cathode circuit of the synchronizing-signal separator tube. That current increases the positive bias of the cathode of that tube, making it nonconductive so that the noise pulse applied to its grid circuit is not reproduced in its output circuit and is not impressed on the scanning generators. Thus, only the synchronizing pulses are passed by the separator tube and applied to the appropriate circuits to maintain the output of the scanning signal generators to the picture tube in step with the deflections of the scanning beam in the transmitter.

Claim 1 (duplicate of patent claim 1) and claim 11 (new in the reissue application) are representative and read as follows (paragraphing ours):

1. A highly noise-immune synchronizing-signal separator system for a television receiver comprising:

first means for supplying a negatively modulated television signal including picture-signal components and synchronizing pulses which tend to be accompanied by unwanted noise signals greater in amplitude than the synchronizing pulses;

second means coupled to said first means for developing a potential representative of and which varies dynamically with the amplitude of said synchronizing pulses;

synchronizing-signal separating means responsive to said first means and dynamically responsive to said potential for separating said synchronizing pulses above the maximum level of said picture-signal components regardless of variations in the amplitude of said synchronizing pulses; and

means coupled

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