Color subcarrier oscillators

Claim 2

A color subcarrier reference oscillator, comprising: a. a transistor having a base, emitter and collector electrode; b. a feedback circuit coupled between the emitter and base electrodes of said transistor for providing a feedback signal of a sufficient magnitude to cause said transistor to sustain self-oscillations, said feedback signal further causing said first transistor to cease conduction for a portion of the cycle of said self-oscillatory frequency; c. a piezoelectric crystal; d. a variable reactance device; and e. means coupling said crystal in a series path with said variable reactance device between said base electrode of said transistor and a point of reference potential, said crystal providing an inductive reactance and said variable reactance device providing a capacitive reactance for determining the frequency of said self-oscillations substantially independent of the input impedance of said transistor.

Claim 3

A color subcarrier reference oscillator, comprising: a. a transistor having a base, collector and emitter electrode; b. means coupled to said electrodes adapted to receive operating bias; c. a resistor coupled between said emitter electrode and a point of reference potential; d. a capacitance coupled between said base electrode and a point of reference potential, said capacitance having a magnitude selected to present a small capacitive reactance at said color subcarrier frequency when compared with that reactance due to the input impedance of said transistor at said base electrode, e. means for coupling an intermediate point of said resistor to an intermediate point of said capacitance to provide feedback to said transistor via said base electrode in a direction to sustain self-oscillation; f. a resonant circuit coupled between said base electrode and a point of reference potential said circuit including a crystal operated in a parallel resonant mode for providing mainly an inductive reactance and a variable reactance device in series therewith for providing mainly a capacitive reactance, said crystal and said variable reactance device determining said frequency of said self-oscillations to correspond substantially to that frequency of said color subcarrier relatively independent of the input impedance of said transistor.

Claim 4

A color subcarrier reference oscillator, comprising: a. a transistor having a base, collector and emitter electrode; b. means coupled to said electrodes adapted to receive operating bias; c. a resistor coupled between said emitter electrode and a point of reference potential; d. a capacitance coupled between said base electrode and a point of reference potential, said capacitance having a magnitude selected to present a small capacitive reactance at said color subcarrier frequency when compared with that reactance due to the input impedance of said transistor at said base electrode, e. means for coupling an intermediate point of said resistor to an intermediate point of said capacitance to provide feedback to said transistor via said base electrode in a direction to sustain self-oscillation; f. a resonant circuit coupled between said base electrode and a point of reference potential said circuit including a crystal operated in a parallel resonant mode for providing mainly an inductive reactance and a variable reactance device in series therewith for providing mainly a capacitive reactance, said crystal and said variable reactance device determining said frequency of said self-oscillations to correspond substantially to that frequency of said color subcarrier relatively independent of the input impedance of said transistor.

Claim 5

In a color television receiver including a sOurce of periodically recurring color synchronizing bursts of a given frequency and phase, burst synchronized apparatus comprising in combination: a. first and second transistors each having a base, collector and emitter electrode; b. a feedback network coupled between the emitter and base electrode of said first transistor for providing a feedback signal of a sufficient magnitude to cause said first transistor to sustain self-oscillations, said feedback signal further causing said first transistor to cease conduction for a portion of the cycle of said self-oscillatory frequency; c. a piezoelectric crystal; d. a variable reactance device; e. means coupling said crystal in a series circuit path with said variable reactance device between said base electrode of said first transistor and a point of reference potential for determining the frequency of said self-oscillations, said crystal providing an inductive reactance and said variable reactance device providing a capacitive reactance; f. means coupling the collector electrode of said first transistor to the base electrode of said second transistor; g. means for biasing said second transistor to operate in a class B mode; h. a parallel resonant tank circuit coupled between the collector of said second transistor and a source of potential, for converting current variations of said second transistor due to said class B mode into substantially sinusoidal signals; i. detector means responsive to said sinusoidal signals and said color bursts to provide a control voltage representative of phase differences therebetween; and j. means coupled between said detector means and said variable reactance device for applying said control voltage to said variable reactance device to alter said phase and frequency of said self-oscillations to correspond to that phase and frequency of said synchronizing bursts.

Claim 6

In a color television receiver including a sOurce of periodically recurring color synchronizing bursts of a given frequency and phase, burst synchronized apparatus comprising in combination: a. first and second transistors each having a base, collector and emitter electrode; b. a feedback network coupled between the emitter and base electrode of said first transistor for providing a feedback signal of a sufficient magnitude to cause said first transistor to sustain self-oscillations, said feedback signal further causing said first transistor to cease conduction for a portion of the cycle of said self-oscillatory frequency; c. a piezoelectric crystal; d. a variable reactance device; e. means coupling said crystal in a series circuit path with said variable reactance device between said base electrode of said first transistor and a point of reference potential for determining the frequency of said self-oscillations, said crystal providing an inductive reactance and said variable reactance device providing a capacitive reactance; f. means coupling the collector electrode of said first transistor to the base electrode of said second transistor; g. means for biasing said second transistor to operate in a class B mode; h. a parallel resonant tank circuit coupled between the collector of said second transistor and a source of potential, for converting current variations of said second transistor due to said class B mode into substantially sinusoidal signals; i. detector means responsive to said sinusoidal signals and said color bursts to provide a control voltage representative of phase differences therebetween; and j. means coupled between said detector means and said variable reactance device for applying said control voltage to said variable reactance device to alter said phase and frequency of said self-oscillations to correspond to that phase and frequency of said synchronizing bursts.

Claim 7

The burst synchronized apparatus according to claim 3 wherein said variable reactance device is a varactor diode.

Claim 8

The burst synchronized apparatus according to claim 4 wherein said means coupling said crystal in a circuit path with said varactor diode includes a resistor in series with said varactor diode of a magnitude selected to limit the voltage across said diode to always maintain said diode in a reverse-biased mode.

Claim 9

The burst synchronized apparatus according to claim 3 wherein said feedback network includes a capacitive divider comprising first and second capacitors coupled in series between the base electrode of said first transistor and a point of reference potential, means coupling the junction between said first and second capacitors to said emitter electrode of said first transistor, said first and second capacitors selected to have a combined reactance at said color synchronizing burst frequency substantially smaller than the normal reactance present at said base electrode due to normal operation of said first transistor.

Claim 10

In a color television receiver including a source of periodically recurring color synchronizing bursts of a given frequency and phase, a burst synchronized oscillator comprising in combination: a. a transistor having a base, emitter and collector electrode; b. a network coupled between the emitter and base electrode for providing feedback in a direction to sustain self-oscillations, said network including a capacitive divider having a reactance at said color synchronizing burst frequency substantially smaller than the normal reactance present at said base electrode due to normal transistor operation; c. a piezoelectric crystal; d. a variable reactance device; e. means coupling said piezoelectric crystal in a series path with said variable reactance device between said base electrode and a point of reference potential, for determining the frequency of said self-oscillation, said crystal providing an inductive reactance and said variable reactance device providing a capacitive reactance f. detector means Responsive to said self-oscillations and said color synchronizing bursts to provide a control voltage representative of phase differences therebetween; and g. means coupled between said detector means and said variable reactance device for applying said control voltage to said variable reactance device to alter said phase and frequency of said self oscillations to correspond to that phase and frequency of said synchronizing bursts, substantially independent of said transistor''s input impedance.

Claim 11

In a color television receiver including a source of periodically recurring color synchronizing bursts of a given frequency and phase, a burst synchronized oscillator comprising in combination: a. a transistor having a base, emitter and collector electrode; b. a network coupled between the emitter and base electrode for providing feedback in a direction to sustain self-oscillations, said network including a capacitive divider having a reactance at said color synchronizing burst frequency substantially smaller than the normal reactance present at said base electrode due to normal transistor operation; c. a piezoelectric crystal; d. a variable reactance device; e. means coupling said piezoelectric crystal in a series path with said variable reactance device between said base electrode and a point of reference potential, for determining the frequency of said self-oscillation, said crystal providing an inductive reactance and said variable reactance device providing a capacitive reactance f. detector means Responsive to said self-oscillations and said color synchronizing bursts to provide a control voltage representative of phase differences therebetween; and g. means coupled between said detector means and said variable reactance device for applying said control voltage to said variable reactance device to alter said phase and frequency of said self oscillations to correspond to that phase and frequency of said synchronizing bursts, substantially independent of said transistor''s input impedance.

Claim 12

In a color television receiver including a source of periodically recurring color synchronizing bursts of a given phase and frequency, burst synchronized apparatus, comprising in combination: a. first and second transistors each having a base, emitter and collector electrode; b. a capacitive divider including first and second capacitors coupled in series between the base electrode of said first transistor and a point of reference potential, the junction therebetween coupled to the emitter electrode of said first transistor, said first and second capacitors selected to provide feedback for said transistor to sustain oscillations, while further providing suitable feedback signal magnitude to cause said transistor to cease conduction for a portion of a cycle at said frequency of oscillations and to further provide a small capacitive reactance at said base electrode when compared with the reactance thereat due to normal transistor operation; c. a circuit path coupled between said base electrode of said first transistor and a point of reference potential including a piezoelectric crystal operating to provide an inductive reactance and a varactor diode for providing a capacitive reactance, said diode and crystal determining said frequency of oscillation substantially independent of said first transistor input impedance; d. a direct coupling path between the collector electrode of said first transistor and the base electrode of said second transistor; e. means coupling the emitter electrode of said second transistor to a point of reference potential to provide with said direct coupling path a bias serving to operate said second transistor in a class B mode; f. a parallel resonant circuit coupled between collector of said second transistor and a point of potential to convert current variations in said second transistor due to said class B mode to substantially sinusoidal waveshapes; g. detector means responsive to said sinusoidal waveshapes and said color synchronizing bursts for providing a control voltage proportional to phase and frequency differences therebetween; and h. means coupling said detector means to said varactor diode for applying said control voltage thereto to alter said frequency and phase of said first transistor oscillations in accordance with said phase and frequency differences.

Claim 13

In a color television receiver including a source of periodically recurring color synchronizing bursts of a given phase and frequency, burst synchronized apparatus, comprising in combination: a. first and second transistors each having a base, emitter and collector electrode; b. a capacitive divider including first and second capacitors coupled in series between the base electrode of said first transistor and a point of reference potential, the junction therebetween coupled to the emitter electrode of said first transistor, said first and second capacitors selected to provide feedback for said transistor to sustain oscillations, while further providing suitable feedback signal magnitude to cause said transistor to cease conduction for a portion of a cycle at said frequency of oscillations and to further provide a small capacitive reactance at said base electrode when compared with the reactance thereat due to normal transistor operation; c. a circuit path coupled between said base electrode of said first transistor and a point of reference potential including a piezoelectric crystal operating to provide an inductive reactance and a varactor diode for providing a capacitive reactance, said diode and crystal determining said frequency of oscillation substantially independent of said first transistor input impedance; d. a direct coupling path between the collector electrode of said first transistor and the base electrode of said second transistor; e. means coupling the emitter electrode of said second transistor to a point of reference potential to provide with said direct coupling path a bias serving to operate said second transistor in a class B mode; f. a parallel resonant circuit coupled between collector of said second transistor and a point of potential to convert current variations in said second transistor due to said class B mode to substantially sinusoidal waveshapes; g. detector means responsive to said sinusoidal waveshapes and said color synchronizing bursts for providing a control voltage proportional to phase and frequency differences therebetween; and h. means coupling said detector means to said varactor diode for applying said control voltage thereto to alter said frequency and phase of said first transistor oscillations in accordance with said phase and frequency differences.

Claim 14

In a color television receiver, a source of reference oscillations of substantially sinusoidal waveshape for use in the synchronous demodulation of a modulated subcarrier component of a received color television signal, comprising: a. a first transistor having base, collector and emitter electrodes; b. a first resonant circuit coupled between said base electrode of said first transistor and a point of reference potential, and selected to resonate at a specified frequency substantially equal to the nominal frequency of said subcarrier; c. a feedback circuit coupled between said emitter and base electrodes of said first transistor for providing a feedback signal of a sufficient magnitude to cause said first transistor to sustain oscillations at said specified frequency, said feedback signal further causing said transistor to cease conduction for a portion of each oscillation cycle, whereby the collector current of said first transistor is subject to nonsinusoidal variations at said specified frequency; d. output circuit means coupled to said collector electrode of said first transistor for developing voltage variationS at said specified frequency of nonsinusoidal waveshape in response to said collector current variations; e. a second transistor having an input electrode and an output electrode f. means, including a coupling between the collector electrode of said first transistor and the input electrode of said second transistor, for rendering said second transistor conducting during the portion of each oscillation cycle when said first transistor ceases conduction and for interrupting the conduction of said second transistor for at least a segment of the remaining portion of each oscillation cycle; and g. means, including a second resonant circuit tuned to a frequency substantially equal to said specified frequency and coupled to said output electrode of said second transistor, for developing said reference oscillations of substantially sinusoidal waveshape in response to the periodic interruptions of conduction of said second transistor.

Claim 15

In a color television receiver, a source of reference oscillations of substantially sinusoidal waveshape for use in the synchronous demodulation of a modulated subcarrier component of a received color television signal, comprising: a. a first transistor having base, collector and emitter electrodes; b. a first resonant circuit coupled between said base electrode of said first transistor and a point of reference potential, and selected to resonate at a specified frequency substantially equal to the nominal frequency of said subcarrier; c. a feedback circuit coupled between said emitter and base electrodes of said first transistor for providing a feedback signal of a sufficient magnitude to cause said first transistor to sustain oscillations at said specified frequency, said feedback signal further causing said transistor to cease conduction for a portion of each oscillation cycle, whereby the collector current of said first transistor is subject to nonsinusoidal variations at said specified frequency; d. output circuit means coupled to said collector electrode of said first transistor for developing voltage variationS at said specified frequency of nonsinusoidal waveshape in response to said collector current variations; e. a second transistor having an input electrode and an output electrode f. means, including a coupling between the collector electrode of said first transistor and the input electrode of said second transistor, for rendering said second transistor conducting during the portion of each oscillation cycle when said first transistor ceases conduction and for interrupting the conduction of said second transistor for at least a segment of the remaining portion of each oscillation cycle; and g. means, including a second resonant circuit tuned to a frequency substantially equal to said specified frequency and coupled to said output electrode of said second transistor, for developing said reference oscillations of substantially sinusoidal waveshape in response to the periodic interruptions of conduction of said second transistor.

Claim 16

Apparatus in accordance with claim 9 wherein said receiver includes means for synchronizing said oscillator with a burst component of said received color television signal, said synchronizing means developing a correction voltage in response to departures from synchronization: wherein said first resonant circuit includes a piezoelectrical crystal and a varactor diode for determining the tuning thereof; and wherein means are provided for causing the reactance exhibited by said diode in said first resonant circuit to vary in accordance with said correction voltage.

Claim 17

In a color television receiver, a source of reference oscillations of substantially sinusoidal waveshape for use in the synchronous demodulation of a modulated subcarrier component of a received color television signal, comprising: a. a first transistor having an input electrode and a pair of output electrodes; b. frequency selective feedback circuit means for providing a positive feedback signal between one of said output electrodes and said input electrode of a sufficient magnitude at a specified frequency substantially equal to the nominal frequency of said subcarrier to cause said first transistor to sustain oscillations at said specified frequency, said feedback signal further causing said transistor to cease conduction for a portion of each oscillation cycle, whereby the output current of said first transistor is subject to nonsinusoidal variations at said specified frequency; c. output circuit means coupled to one of said output electrodes of said first transistor for developing voltage variations at said specified frequency of nonsinusoidal waveshape in response to said output current variations; d. a second transistor having an input electrode and an output electrode; e. means, including a coupling between said output circuit means and electrode; input electrode of said second transistor, for rendering said second transistor conducting during the portion of each oscillation cycle when said first transistor ceases conduction and for interrupting the conduction of said second transistor for at least a segment of the remaining portion of each oscillation cycle; and f. means, including a second resonant circuit tuned to a frequency substantially equal to said specified frequency and coupled to said output electrode of said second transistor, for developing said reference oscillations of substantially sinusoidal waveshape in response to the periodic interruptions of conduction of said second transistor.

Claim 18

In a color television receiver, a source of reference oscillations of substantially sinusoidal waveshape for use in the synchronous demodulation of a modulated subcarrier component of a received color television signal, comprising: a. a first transistor having an input electrode and a pair of output electrodes; b. frequency selective feedback circuit means for providing a positive feedback signal between one of said output electrodes and said input electrode of a sufficient magnitude at a specified frequency substantially equal to the nominal frequency of said subcarrier to cause said first transistor to sustain oscillations at said specified frequency, said feedback signal further causing said transistor to cease conduction for a portion of each oscillation cycle, whereby the output current of said first transistor is subject to nonsinusoidal variations at said specified frequency; c. output circuit means coupled to one of said output electrodes of said first transistor for developing voltage variations at said specified frequency of nonsinusoidal waveshape in response to said output current variations; d. a second transistor having an input electrode and an output electrode; e. means, including a coupling between said output circuit means and electrode; input electrode of said second transistor, for rendering said second transistor conducting during the portion of each oscillation cycle when said first transistor ceases conduction and for interrupting the conduction of said second transistor for at least a segment of the remaining portion of each oscillation cycle; and f. means, including a second resonant circuit tuned to a frequency substantially equal to said specified frequency and coupled to said output electrode of said second transistor, for developing said reference oscillations of substantially sinusoidal waveshape in response to the periodic interruptions of conduction of said second transistor.