Search tuning system for television receiver

Abstract

A search tuning type channel detector system for television receivers. When afc voltage of a tuner has attained a first predetermined voltage level, frequency sweeping direction for tuning is reversed and stopped thereby to tune the tuner at an optimum tuning frequency. Means are provided to allow the inversion as well as stoppage of the frequency sweeping only when afc voltage has attained a second predetermined voltage level, thereby to exclude possible erroneous operation due to noise or the like spurious signal components.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a channel selector apparatus suited to be used for an electronic tuner having a search function in a television receiver.

2. Description of the Prior Art

For the channel selector of television receivers, there have been hitherto known and widely used search type channel selectors and preset search type channel selection apparatus. In the former case, tuning voltage applied to the electronic tuner is swept or scanned to a , the siganla noise component superposed on the AFC voltage and assures that the tuner can receive the TV signal at a selected channel in a much stabilized state at the optimum tuning frequency. Further, because a filtering capacitor need not be connected to the input terminal for the AFC voltage, the frequency sweeping rate can be enhanced.

Claims

1. A search tuning system for a television receiver comprising:

a tuner having frequency which is increased monotonously in response to application of a tuning voltage of a magnitude increased which is changed monotonously in one direction and adapted to produce a first afc voltage at a first frequency and a fourth frequency higher than said first frequency upon reception of a television signal, said first afc voltage being different from an afc voltage in the quiescent state, said tuner being further adapted to produce a second afc voltage at a second frequency higher than said first frequency as well as at a third frequency which is higher than said second frequency and lower than said fourth frequency;

a sweep voltage generator circuit for supplying said tuning voltage to said tuner;

a sweep control circuit for supplying a control signal to said sweep voltage generator circuit thereby to control increasing, decreasing and holding of said tuning voltage;

a first voltage detector circuit for detecting when the afc voltage of said tuner has attained said first voltage thereby to produce a first detection signal to be supplied to said sweep control circuit;

wherein said sweep voltage generator circuit is controlled by said sweep control circuit unless said first detector circuit produces said first detection signal, whereby said tuning voltage applied to said tuner is caused to vary in said one direction thereby to sweep said tuning frequency, while upon reception of a television signal during said frequency sweeping, the sweeping of said tuning voltage is inverted in response to generation of said first detection signal from said first detector circuit, wherein said sweep control circuit responds to disappearance of said first detection signal in the course of said inverted sweeping thereby to hold the instantaneous tuning voltage and stop the sweeping of said tuning frequency;

said search tuning system further including a second voltage detector circuit for producing a second detection signal when the afc voltage of said tuner has attained said second afc voltage and supplying said second detection signal to said sweep control circuit, wherein, upon detection of said second detection signal through said second detector circuit in the course of said frequency sweeping in said one direction, said second detection signal is applied to said sweep control circuit which then controls said sweep voltage generator circuit thereby to invert such that the frequency sweeping direction is allowed to be inverted and hold the corresponding tuning voltage invariably the inverted sweeping is continued until application of said second detection signal, while upon production of said second detection signal from said second voltage detector circuit said second detection signal is supplied to said sweep control circuit to be stored therein for preparation of stopping said inverted frequency sweeping, which is then realized by holding invariably said tuning voltage from said sweep voltage generator circuit in response to application of said first detection signal produced from said first detection circuit when the afc voltage has attained said first afc voltage at said first frequency.

2. A search tuning system for a television receiver comprising:

a tuner having a tuning frequency increased monotonously in response to application of a tuning voltage of a magnitude increased which is changed monotonously in one direction and adapted to produce a first afc voltage at a first frequency and a fourth frequency higher than said first frequency upon reception of a television signal, said first afc voltage being different from an afc voltage in the quiescent state, said tuner being further adapted to produce a second afc voltage at a second frequency higher than said first frequency as well as at a third frequency which is higher than said second frequency and lower than said fourth frequency;

a sweep voltage generator circuit for supplying said tuning voltage to said tuner;

a sweep control circuit for supplying a control signal to said sweep voltage generator circuit thereby to control increasing, decreasing and clamping of said tuning voltage;

a first voltage detector circuit for detecting when the afc voltage of said tuner has attained said first voltage thereby to produce a first detection signal to be supplied to said sweep control circuit;

wherein said sweep voltage generator circuit is controlled by said sweep control circuit unless said first detector circuit produces said first detection signal, whereby said tuning voltage applied to said tuner is caused to vary in said one direction thereby to sweep said tuning frequency, while upon reception of a television signal during said frequency sweeping, the sweeping of said tuning voltage is inverted in response to disappearance of said first detection signal from said first detector circuit upon increasing of the afc voltage of said tuner beyond said first afc voltage at said fourth frequency in succession to generation of said first detection signal by said first detector circuit, wherein said sweep control circuit responds to disappearance of said first detection signal in succession to generation thereof in the course of said inverted sweeping thereby to hold the instantaneous tuning voltage and stop the sweeping of said tuning frequency;

said search tuning system further including a second voltage detector circuit for producing a second detection signal when afc voltage of said tuner becomes lower than said second afc voltage and supplying said second detection signal to said sweep control circuit, wherein, when the afc voltage has attained said second voltage at said second or third frequency, said second voltage detector produces said second detection signal which is then applied to said sweep control circuit which in turn controls said sweep voltage generator circuit thereby to invert such that the frequency sweeping direction is allowed to be inverted and hold the corresponding tuning voltage invariably the inverted sweeping is continued until application of a further second detection signal from said second voltage detector circuit, while upon production of said second detection signal from said second voltage detector circuit said second detection signal is supplied to said sweep control circuit to be stored therein for preparation of stopping said inverted frequency sweeping, which is then realized by holding invariably said tuning voltage from said sweep voltage generator circuit in response to application of said first detection signal produced from said first detection circuit when the afc voltage has attained said first afc voltage at said first frequency.

3. A search tuning system for a television receiver comprising:

a tuner having a tuning frequency increased monotonously in response to application of a tuning voltage of a magnitude increased which is changed monotonously in one direction and adapted to produce a first afc voltage at a first frequency and a fourth frequency higher than said first frequency upon reception of a television signal, said first afc voltage being different from an afc voltage in the quiescent state, said tuner being further adapted to produce a second afc voltage at a second frequency higher than said first frequency as well as at a third frequency which is higher than said second frequency and lower than said fourth frequency;

a sweep voltage generator circuit for supplying said tuning voltage to said tuner;

a sweep control circuit for supplying a control signal to said sweep voltage generator circuit thereby to control increasing, decreasing and holding of said tuning voltage;

a first voltage detector circuit for detecting when the afc voltage of said tuner has attained said first voltage thereby to produce a first detection signal to be supplied to said sweep control circuit;

wherein said sweep voltage generator circuit is controlled by said sweep control circuit unless said first detector circuit produces said first detection signal, whereby said tuning voltage applied to said tuner is caused to vary in said one direction thereby to sweep said tuning frequency, while upon reception of a television signal during said frequency sweeping, the sweeping of said tuning voltage is inverted in response to disappearance of said first detection signal from said first detector circuit upon increasing of afc voltage of said tuner beyond said first afc voltage at said fourth frequency in succession to generation of said first detection signal by said first detector circuit, wherein said sweep control circuit responds to disappearance of said first detection signal in succession to generation thereof in the course of said inverted sweeping thereby to hold the instantaneous tuning voltage and stop the sweeping of said tuning frequency;

said search tuning system further including a second voltage detector circuit for producing a second detection signal when the afc voltage of said tuner becomes lower than said second afc voltage and supplying said second detection signal to said sweep control circuit, wherein said sweep control circuit is adapted to control said sweep voltage generator circuit so as to effect the frequency sweeping continuously in said one direction until application of said second detection signal from said second detection circuit, while upon detection of the afc voltage having attained said second voltage at said second frequency, said second detector circuit supplies said second detection signal to said sweep control circuit to be stored therein for preparation of inversion of the frequency sweeping direction, which is then realized by said sweep voltage generator circuit in response to application of said first detection signal produced from said first detection circuit when the afc voltage has attained said first voltage at said fourth frequency, wherein, upon detection of said second detection signal through said second detector circuit at said third frequency, said second detection signal is applied to said sweep control circuit which then controls said sweep voltage generator circuit thereby to invert such that the frequency sweeping direction is allowed to be inverted and hold the corresponding tuning voltage invariably the inverted sweeping is continued until application of said second detection signal from said second voltage detector circuit, while upon production of said second detection signal from said second voltage detector circuit said second detection signal is supplied to said sweep control circuit to be stored therein for preparation of stopping said inverted frequency sweeping, which is then realized by holding invariably said tuning voltage from said sweep voltage generator circuit in response to application of said first detection signal produced from said first detection circuit when the afc voltage has attained said first afc voltage at said first frequency.

4. For use in a television receiver including a tuner having a tuning frequency which varies in proportion to the magnitude of an applied tuning voltage, and which produces an afc signal of a first voltage level both at a first tuning frequency and a fourth tuning frequency higher than said first tuning frequency upon reception of a television signal and produces an afc signal of a second voltage level at a second tuning frequency higher than said first tuning frequency as well as at a third tuning frequency which is higher than said second tuning frequency and lower than said fourth tuning frequency, a search tuning system comprising:

sweep voltage generator means for selectively applying to said tuner a tuning voltage of continuously-changing magnitude in one direction, continuously-changing magnitude in the direction opposite said one direction or a constant magnitude in response to receipt of first, second or third control signals, respectively;

first voltage detector means responsive to said afc signal for producing a first detection signal when said afc signal is at said first voltage level;

second voltage detector means responsive to said afc signal for producing a second detection signal when said afc signal is at said second voltage level; and

sweep control means responsive to said first and second voltage detector means for controlling said sweep voltage generator means to generate said first control signal until said first detection signal is generated subsequent to generation of said second detection signal, to generate said second control signal upon generation of said first detection signal subsequent to generation of said second detection signal and said first control signal, and to generate said third control signal upon generation of said first detection signal subsequent to generation of said second detection signal and said second control signal.

5. A search tuning system as defined in claim 4, wherein said sweep control means includes first means responsive to the output of said second voltage detector means for producing an output upon receipt of said second detection signal and second means normally producing said first control signal and responsive to said first detector means and the output produced by said first means for ceasing to produce said first control signal.

6. A search tuning system as defined in claim 5, wherein said sweep control means further includes third means responsive to the output of said second detector means and the lack of production of said first control signal by said second means for producing an output, and fourth means responsive to the output of said first detector means and the output of said third means for producing said third control signal.

7. A search tuning system as defined in claim 6, wherein said sweep control means further includes gate means for producing said second control signal in response to the logical sum of the outputs of said second and fourth means.

8. A search tuning system as defined in claims 6 or 7, wherein said first, second, third and fourth means include bistable devices.

9. A search tuning system as defined in claim 4, wherein said sweep control means includes means for storing the receipt of successive ones of said first and second detection signals and means responsive to said storing means for producing said first, second and third control signals.

10. A search tuning system as defined in claim 9, wherein said storing means includes a plurality of bistable devices connected in cascade.

11. A search tuning system for a television receiver comprising:

a tuner having a tuning frequency increased monotonously in response to application of a tuning voltage of a magnitude changed monotonously in one direction and adapted to produce an afc voltage signal assuming a first afc voltage at a first frequency and a fourth frequency higher than said first frequency upon reception of a television signal, said afc signal assuming a second afc voltage at a second frequency higher than said first frequency as well as at a third frequency which is higher than said second frequency and lower than said fourth frequency; a sweep voltage generator circuit for supplying said tuning voltage to said tuner; a sweep control circuit for supplying a control signal to said sweep voltage generator circuit thereby to control increasing, decreasing and clamping of said tuning voltage; and a first voltage detector circuit for detecting the fact that the afc voltage signal from said tuner has attained said first voltage thereby to produce a first detection signal to be supplied to said sweep control circuit; wherein said sweep voltage generator circuit is controlled by said sweep control circuit such that the sweeping of said tuning voltage is inverted in response to said first detection signal from said first detector circuit as said afc voltage signal passes beyond said first afc voltage at said fourth frequency, the inverted sweeping of said tuning voltage is stopped in response to said first detection signal from said first detector circuit as said afc voltage signal passes beyond said first afc voltage at said first frequency, and said tuning voltage is held in a state of said first afc voltage at said first frequency;

(a) said search tuning system further comprises a second detector circuit for detecting the fact that the afc voltage signal from said tuner has attained said second voltage thereby to produce a second detection signal to be supplied to said sweep control circuit; and

(b) said sweep control circuit includes:

means for inhibiting inversion of the tuning voltage sweeping direction until after generation of said second detection signal by said second voltage detector circuit at said second frequency and for detecting and storing said second detection signal when it is generated thereby making preparations for inversion of the tuning voltage sweeping direction, and

means for inhibiting, after the inversion of the tuning voltage sweeping direction at said fourth frequency, stoppage of the tuning voltage sweeping in the inverted direction until after regeneration of said second detection signal by said second voltage detector circuit at said third frequency and for detecting and storing said second detection signal when it is regenerated thereby making preparations for the stoppage of the tuning voltage sweeping.