Blanking circuits for television receivers

Claim 2

In a television receiver of the type employing a kinescope having an electron beam and a circuit for deflecting said beam in one of two mutally perpendicular directions, said deflection circuit being of the type including a first, normally conductive active device and a second, normally non-conductive active device coupled in an oscillator configuration for producing a sweep wave form having a relatively long charge time determined by the conduction of said first active device and a relatively fast discharge time determined by the conduction of said second active device, said normally conductive first device being rendered nonconductive and said normally non-conductive second device being rendered conductive in response to a synchronizing signal applied during a retrace interval associated with said deflection circuit, in combination therewith apparatus for providing a blanking signal during said retrace interval, comprising: a. first means serially coupled in the current path of said second active device and responsive to its current flow during the conductive state thereof for providing a control signal indicative of the occurrence of said retrace interval, b. a third active device having an input electrode coupled to receive said control signal, a common electrode coupled to a point of reference potential and an output electrode, said third device being responsive to the application of said control signal to present a low impedance between its output and common electrodes during said retrace interval, and c. second means coupling the output electrode of said third active device to said kinescope to change the bias thereon and cause the electron beam of said kinescope to cut off during said interval.

Claim 3

A blanking circuit for a television receiver including an amplifier direct coupled to a kinescope producing an electron beam, said amplifier including a plurality of stages and said receiver including deflection wave form generating apparatus for producing a deflection wave form having a relatively long scanning interval determined by the conduction of an included first, normally conductive active device and a relatively short retrace interval determined by the conduction of an included second, normally non-conductive active device, with said first and second active devices being arranged in an oscillator configuration, the frequency of which is controlled by the charging rate of a timing capacitor coupled to discharge through the second of said active devices in response to the application of a synchronizing signal applied during said retrace interval to render said normally conductive first device non-conductive and to render said normally non-conductive second device conductive, comprising in combination: a. means serially coupled in the current path of said second active device and responsive to its current flow during the conductive state thereof for producing a pulse output during said retrace interval, and b. a transistor having base, collector and emitter electrodes, said emitter electrode being coupled to a source of reference potential, said collector electrode being coupled to said amplifier, and said base electrode being coupled to said means and responsive to the occurrence of said pulse to cause said transistor to saturate and thereby provide a low impedance between its collector and emitter electrodes, to alter both the bias on said amplifier and the bias on said kinescope in a direction to cut off the electron beam of said kinescope during said retrace interval.

Claim 4

A blanking circuit for a television receiver including an amplifier direct coupled to a kinescope producing an electron beam, said amplifier including a plurality of stages and said receiver including deflection wave form generating apparatus for producing a deflection wave form having a relatively long scanning interval determined by the conduction of an included first, normally conductive active device and a relatively short retrace interval determined by the conduction of an included second, normally non-conductive active device, with said first and second active devices being arranged in an oscillator configuration, the frequency of which is controlled by the charging rate of a timing capacitor coupled to discharge through the second of said active devices in response to the application of a synchronizing signal applied during said retrace interval to render said normally conductive first device non-conductive and to render said normally non-conductive second device conductive, comprising in combination: a. means serially coupled in the current path of said second active device and responsive to its current flow during the conductive state thereof for producing a pulse output during said retrace interval, and b. a transistor having base, collector and emitter electrodes, said emitter electrode being coupled to a source of reference potential, said collector electrode being coupled to said amplifier, and said base electrode being coupled to said means and responsive to the occurrence of said pulse to cause said transistor to saturate and thereby provide a low impedance between its collector and emitter electrodes, to alter both the bias on said amplifier and the bias on said kinescope in a direction to cut off the electron beam of said kinescope during said retrace interval.

Claim 5

The blanking circuit of claim 2 wherein the discharge current path for said timing capacitor is through said second active device and partly through the base to emitter electrode path of said transistor.

Claim 6

The blanking circuit according to claim 2 wherein said means serially coupled in series with said second active device includes a resistor.

Claim 7

The blanking circuit according to claim 2 wherein said active devices are vacuum tubes and said transistor is an NPN transistor.

Claim 8

The blanking circuit according to claim 2 wherein said retrace interval is the vertical retrace interval of an applied television signal.