DEFLECTION APPARATUS HAVING RASTER POSITIONING CIRCUITRY

CROSS REFERENCE TO RELATED APPLICATIONS This application is related to concurrently filed applications entitled "Method for adjusting video display apparatus" with Attorney's docket number PU050086 and "Method for adjusting convergence in a television receiver" with Attorney's docket number PU050150, all by the same inventor.

FIELD OF THE INVENTION The present invention generally relates to deflection systems used in devices such as television signal receivers and/or monitors, and more particularly, to a deflection apparatus having raster positioning circuitry for enabling deflection functions including a centering function.

BACKGROUND OF THE INVENTION

Deflection systems utilized in devices such as television signal receivers or monitors often include circuitry that allows for the adjustment of the raster on the face of a kinescope tube. In particular, such adjustments are useful for correcting picture offsets in devices due to local magnetic field changes. For example, when a device such as a television signal receiver is physically moved, the magnetic field around the tube(s) may change and thereby cause the picture to rotate or become off-centered.

To correct this condition, the aforementioned adjustments including a centering function may be performed to restore the picture to its proper alignment.

The centering function may for example be accomplished by causing a direct current

(DC) of selected polarity and magnitude to flow through one or more deflection windings. The need for this centering function may increase as overscan of the kinescope tube is reduced, that is, as the raster width approaches the width of the kinescope tube face.

While circuitry for enabling a centering function is generally known in the art, such designs may be deficient for various reasons. For example, designs such as the one shown in U.S. Patent No. 6,621 ,240 may utilize a reversing switch to control a centering function. With such designs, if a slight imbalance in positive and negative currents is present in the deflection windings, picture centering may be impossible and an offset in picture position (i.e., picture jump) may occur upon switching. Moreover, electrical transients that can cause component overstress and failure may occur as a result of the switching. This may require the use of more expensive components, and therefore increase product cost. Accordingly, there is a need for a deflection apparatus having raster positioning circuitry which avoids the foregoing and/or other problems. The specification of the present invention describes herein two exemplary embodiments for such a deflection apparatus.

SUMMARY OF THE INVENTION In accordance with an aspect of the present invention, an apparatus for enabling a deflection function is disclosed. According to an exemplary embodiment, the apparatus comprises a first rectifier for conducting a first current having a first polarity. A first transistor is coupled in series with the first rectifier for conducting the first current. A second rectifier conducts a second current having a second polarity. A second transistor is coupled in series with the second rectifier for conducting the second current. Control circuitry controls the conduction of the first transistor and the second transistor to control a ratio of a magnitude of the first current to a magnitude of the second current.

In accordance with another aspect of the present invention, a television signal receiver is disclosed. According to an exemplary embodiment, the television signal receiver comprises first rectifying means for conducting a first current having a first polarity. First switching means is coupled in series with the first rectifying means for conducting the first current. Second rectifying means conducts a second current having a second polarity. Second switching means is coupled in series with the second rectifying means for conducting the second current. Control means controls

the conduction of the first switching means and the second switching means to control a ratio of a magnitude of the first current to a magnitude of the second current.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: FIG. 1 is a deflection apparatus having raster positioning circuitry according to an exemplary embodiment of the present invention;

FIG. 2 shows currents in resistor R2 and horizontal deflection windings LY of FIG. 1 according to an exemplary embodiment of the present invention; and

FIG. 3 is a deflection apparatus having raster positioning circuitry according to another exemplary embodiment of the present invention.

The exemplifications set out herein illustrate preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and more particularly to FlG. 1 , a deflection apparatus having raster positioning circuitry according to an exemplary embodiment of the present invention is shown. The deflection apparatus of FIG. 1 comprises Darlington switches 100 and 200, power rectifier 300, optocoupler 400, centering control circuit 500, horizontal drive circuit 600, horizontal deflection windings LY, and various other circuit elements. According to an exemplary embodiment, the deflection apparatus of FIG. 1 may be included as a component of a television signal receiver, or other device that performs and/or enables deflection functions.

Darlington switch 100 comprises transistors Q101 and Q102, resistor R101 , and diode D101. Darlington switch 200 comprises transistors Q201 and Q202,

resistor R202, and diode D201. Power rectifier 300 comprises diodes D301 to D304, zener diode D305, and capacitor C301. Optocoupler 400 comprises transistor Q401, amplifier 401, light emitting diode (LED) D401, and resistor R401. Centering control circuit 500 comprises transistor Q501 , pulse width one shot 501 , delay one shot 502, and digital-to-analog converter (D/A) 503. Horizontal drive circuit 600 comprises transistor Q601, diode D601, retrace capacitor C601, power supply 601, driver 602, flyback transformer TOW1 , linearity inductor LJJN, and S shaping capacitor C_S. Other circuit elements of FIG. 1 include resistors R1 to R4, diodes D1 and D2, capacitors C40 and C41 , and inductor L_SHUNT. Preferred values for the foregoing circuit elements are shown in FIG. 1.

Horizontal drive circuit 600 is energized by power supply 601 that generates a supply voltage B+. Driver 602 is responsive to an input signal, H SYNC, provided at a horizontal deflection frequency (e.g., 31.468 KHz for 2H scan) and generates a drive control signal to control the switching of transistor Q601. The collector of transistor Q601 is coupled to flyback transformer TOW1 , diode D601 and retrace capacitor C601. The collector of transistor Q601 is additionally coupled to horizontal deflection windings LY to form a retrace resonant circuit. Horizontal deflection windings LY are coupled in series with linearity inductor LJJN and S shaping capacitor C_S. Horizontal drive circuit 600 is capable of producing a deflection current through horizontal deflection windings LY in a known manner.

Centering control circuit 500 is operative to control a horizontal centering function of the deflection apparatus of FIG. 1. According to an exemplary embodiment, delay one shot 502 receives the H SYNC signal and applies thereto a phase delay between approximately zero and approximately one half of the horizontal scan cycle responsive to a digital centering control signal that is converted to an analog format via D/A 503. Pulse width one shot 501 produces a pulse having a length equal to approximately one half of the horizontal scan cycle responsive to the output signal provided from delay one shot 502. This pulse lights LED D401 and turns on transistor Q401 of optocoupler 400, which may for example be embodied as

a Sharp™ model PC91 OLONSZ optocoupler or an equivalent coupling element. Through transistor Q401 and diodes D1 and D2, turn on bias current may be diverted away from Darlington switches 100 and 200, thereby turning them off for one half of the horizontal scan cycle when LED D401 is lit. Conversely, when LED D401 is not lit (and transistor Q401 is turned off), Darlington switches 100 and 200 are fully conductive throughout the horizontal scan cycle because of turn on bias current through either resistor R3 or R4, respectively.

As indicated in FIG. 1 , Darlington switches 100 and 200 are coupled in inverse series and thereby control the current through inductor L_SHUNT and horizontal deflection windings LY. Darlington switch 100 includes transistors Q101 and Q102 which conduct a first current having a first polarity. Diode D201 of

Darlington switch 200 acts as a rectifier coupled in series with transistors Q101 and

Q102 of Darlington switch 100 and also conducts this first current. Similarly, Darlington switch 200 includes transistor Q201 and Q202 which conduct a second current having a second polarity opposite to -the first polarity. Diode D101 of

Darlington switch 100 acts as a rectifier coupled in series with transistors Q201 and

Q202 of Darlington switch 200 and also conducts this second current. Power rectifier 300 is operative to provide 5 volts DC power to optocoupler 400. Capacitors C40 and C41 perform a dual function of limiting voltage across Darlington switches

100 and 200, and limiting current to power rectifier 300.

According to principles of the present invention, it is the ratio of the magnitude of the first current conducted by Darlington switch 100 to the magnitude of the second current conducted by Darlington switch 200 that controls the horizontal centering function of the deflection apparatus of FIG. 1. In particular, by controlling the amount of delay applied to the H SYNC signal by delay one shot 502, the turn off pulse for Darlington switches 100 and 200 can be timed to block the first current, the second current, or a proportional combination of the first and second currents provided to inductor L_SHUNT. The net current present in inductor L_SHUNT has a DC component that also flows to horizontal deflection windings LY. This DC current

controls the horizontal centering function performed by horizontal deflection windings LY, and may exhibit various amplitudes positive or negative, or zero when the first and second currents respectively provided by Darlington switches 100 and 200 are equal.

Referring to FIG. 2, graphs illustrating currents in resistor R2 and horizontal deflection windings LY of FIG. 1 according to an exemplary embodiment of the present invention are shown. In particular, the upper graph of FIG. 2 shows currents in resistor R2, and the lower graph of FIG. 2 shows currents in horizontal deflection windings LY. FIG. 2 represents a circuit function test result where pulse width one shot 501 is triggered with a frequency slightly different from the horizontal frequency. Different conditions of delay one shot 502 are simulated in successive cycles so that the full range of picture centering can be evaluated. In FIG. 2, the horizontal scan cycle is 27 μS consisting of 22 μS of scan and 5 μS of retrace. A nominal deflection current of +/- 6 amps peak-to-peak is supplied to the parallel combination of horizontal deflection windings LY and inductor L_SHUNT. Transistor Q401 is turned on for 13 μS every 27.5 μS. The frequency difference between the output signal of transistor Q401 and the horizontal scan rate causes the phase of the 13 μS turn on time of transistor Q401 to sweep through the horizontal scan cycle every 1.5 mS. In FIG. 2, the variation that can be seen in the positive peaks of the current in horizontal deflection windings LY is due to a variation in the average current provided by Darlington switches 100 and 200 and causes the resulting picture to vibrate left and right. If the phase of the output signal of transistor Q401 is held constant with respect to the horizontal scan cycle, a level in the variation cycle can be selected to achieve desired centering. The large peaks seen in the resistor R2 current are caused by inductive switching transients and do not contribute significant energy to the average current.

Referring now to FIG. 3, a deflection apparatus including raster positioning circuitry according to another exemplary embodiment of the present invention is shown. The deflection apparatus of FIG. 3 comprises horizontal drive circuit 101 ,

horizontal deflection winding L350, potentiometer R451 , Darlington switches Q453 and Q454, and various other circuit elements. According to an exemplary embodiment, the deflection apparatus of FIG. 3 may be included as a component of a television signal receiver, or other device that performs deflection functions.

Horizontal drive circuit 101 and horizontal deflection winding L350 of FIG. 3 may be substantially identical to horizontal drive circuit 600 and horizontal deflection windings LY of FIG. 1 , respectively. Potentiometer R451 includes an adjustable tap 20 that is moveable between a first end 451a and a second end 451 b of potentiometer R451. Darlington switch Q453 comprises transistors Q453a and Q453b, resistors R601 and R602, and diode D60. Darlington switch Q454 comprises transistors Q454a and Q454b, resistors R603 and R604, and diode D61. Other circuit elements of FIG. 3 include resistors R450, R453, R457 and R458, capacitors C470 and C471 , and inductor L452. Preferred values for the foregoing circuit elements are shown in FIG. 3.

As indicated in FIG. 3, Darlington switches Q453 and Q454 are connected in inverse series and thereby control the current through inductor L452 and horizontal deflection winding L350. Darlington switch Q453 includes transistors Q453a and Q453b which conduct a first current having a first polarity. Diode D61 of Darlington switch Q454 acts as a rectifier coupled in series with transistors Q453a and Q453b of Darlington switch Q453 and also conducts this first current. Similarly, Darlington switch Q454 includes transistor Q454a and Q454b which conduct a second current having a second polarity opposite to the first polarity. Diode D60 of Darlington switch Q453 acts as a rectifier coupled in series with transistors Q454a and Q454b of Darlington switch Q454 and also conducts this second current.

According to principles of the present invention, it is the ratio of the magnitude of the first current conducted by Darlington switch Q453 to the magnitude of the second current conducted by Darlington switch Q454 that controls the horizontal centering function of the deflection apparatus of FIG. 3. In particular, during a given

horizontal scan cycle, the current in inductor L452 and horizontal deflection winding L350 flows in a first direction and then in an opposing second direction, thereby completing one AC cycle. In the first direction, current flows through Darlington switch Q453 and diode D61. In the second opposing direction, current flows through Darlington switch Q454 and diode D60. The conduction duty cycle of Darlington switch Q453 is controlled by a positive voltage developed during a first portion of the horizontal scan cycle between first end 451a of potentiometer R451 and adjustable tap 20. The conduction duty cycle of Darlington switch Q454 is controlled by a positive voltage developed during a second portion of the horizontal scan cycle between second end 451b of potentiometer R451 and adjustable tap 20. In this manner, one or the other of Darlington switches Q453 and Q454 is turned off when tap 20 approaches either first end 451a or second end 451b because no voltage is developed when the resistance between tap 20 and first end 451a or second end 451b approaches zero.

When one of the Darlington switches Q453 and Q454 is turned off, a net DC current flows into inductor L452 and horizontal deflection winding L350 and thereby causes off center deflection of the raster. When tap 20 is in the center position (i.e., centered between first end 451a and second end 451b of potentiometer R451), equal drive is supplied to both Darlington switches Q453 and Q454 and equal and opposite DC currents that cancel one another are produced in inductor L452 and horizontal deflection winding L350. Accordingly, picture centering occurs when tap 20 is in the center position. As tap 20 is moved between the center position and first end 451a or second end 451b of potentiometer R451 , the net DC current in inductor L452 and horizontal deflection winding L350 in one direction gradually increases while the net DC current in the opposing direction gradually decreases. This allows adjustment of a continuous series of centering positions.

As described herein, the present invention provides a deflection apparatus having raster positioning circuitry for enabling deflection functions including a centering function. While this invention has been described as having a preferred

design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.