KR820002357B1 - Automatic kinescope bias control circuit - Google Patents

Abstract

Apparatus for automatically controlling the bias of an image reproducing color kinescope in a system including a plurality of video driver states for supplying image representative video signals to respective intensity control electrodes of the electron guns of the kinescope. The output of each driver stage is coupled to an operating supply voltage via a load impedance. The electron gun currents (e.g., Cathode currents) are sensed during image blanking intervals of the video signal to provide respective control voltages representative of the electron gun blanking current levels.

Description

Automatic Kinescope Bias Control Circuit

1 is a circuit schematic diagram schematically showing a portion of a color television receiver using a device constructed in accordance with the present invention.

2 to 4 are circuit diagrams showing another embodiment of the present invention.

The present invention relates to an apparatus for automatically controlling the bias of an image reproduction kinescope in a video signal processing system such as a color television receiver or an equivalent system to indicate an appropriate cut-off blanking level for each electron gun of the kinescope. .

The color image reproduction kinescope included in the color television receiver includes a plurality of electron guns each activated by the red, green and blue color indicator signals derived from the received composite color television signal. Since the reproduced color image is determined by one or a combination of these signals, the optimal reproduction of the color image requires the accuracy of all drive levels at which the relative proportions of these color signals are from white to gray to black. . In this regard, the three electron guns must exhibit a very reduced conductivity or appear cut-off.

Optimal reproduction of color images and grayscale tracking of kinescopes have the opposite effect when the bias of the electron gun is out of pre-determined levels, causing undesirable kinescope cut-off errors. These cut-off errors appear as color tints on the displayed monochrome image and overset the color fidelity of the displayed color image. These cut-off errors are caused by the change function and temperature effects and instantaneous kinescope "flashover" including changes in the operating characteristics of the kinescope-related circuits.

Since it is desirable to calibrate all luminance levels by proportioning the color signals to the kinescope, color television receivers represent a device for inviting the kinescope and associated circuits in a known set up and operation mode of the receiver. In simple terms, a usage switch having "normal" and "used" states is operatively associated with the receiver signal processing circuit and the kinescope. In the "use" state, the video signals are separated from the kinescope and the vertical scan collapses. Each electron gun bias is adjusted to represent the desired blanking and cut-off current (eg, several micro amps) for each electron gun. This adjustment causes the kinescope to be properly blanked or cut-off in the absence of an applied video signal or in response to the black reference level of the video signal, and the color signals to be appropriately proportional to all luminance levels. The kinescope drive circuits associated with each electron gun are then adjusted to the desired gain (e.g., to compensate for the kinescope fluorescence effects) to drive the red, blue and green signals at an appropriate rate when the receiver is operating normally.

Kinescope cut-off adjustments are time-consuming and inconvenient and must be performed several times during the kinescope lifetime. Also, the kinescope cut-off and gain adjustment often interoperate, requiring continuous adjustment. Therefore, it is better to eliminate the need for this adjustment by allowing it to be automatically adjusted by the circuitry in the receiver.

Automatic kinescope bias control adjustments can generate kinescope bias control voltages and apply this voltage to the kinescope bias control circuit in such a way as to create minimal interaction between the video signal and the control voltage coupled to the kinescope. . In addition, automatic bias control adjustment can be applied to kinescopes (eg, magnetic inversion “in-line”) with control grids activated from a common source, as well as kinescopes with activated control grids connected to the cathodes of each electron gun. It should be applicable to "type kinescopes".

According to the present invention, an automatic kinescope bias control device that satisfies these criteria is provided in a system for processing an image display video signal having a periodical playback image period and a breaking period.

The system includes an image reproduction kinescope having a sensitivity control electrode and a video amplifier for supplying a video signal finally amplified from the output of the amplifier to the kinescope electrode. The output circuit of this amplifier includes a load impedance coupled between the amplifier output and the operating panel. The sensing circuit senses the magnitude of the current conducted to the kinescope electrode and is coupled to the sensing circuit and the signal transition circuit operating during the blanking period of the video signal receives a control voltage representing the bias of the kinescope electrode current from the desired level during the blanking period. Induce. This control voltage is coupled to the amplifier output circuit and is independent of the constant current and video signal flowing through the load impedance and changes the constant voltage of the amplifier output in a direction that minimizes the difference between the sensed kinescope electrode blanking current and the desired blanking current level. Let's do it.

According to one embodiment of the invention, the cathode blanking current is sensed by an optical coupling circuit comprising a light emitting diode in the cathode current path and a photosensitive diode optically coupled to the light emitting diode. The light emitting diode emits an amount of light proportional to the cathode blanking current, and the light is sensed by the light sensing diode to have a corresponding output signal from the indicated control voltage.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

Referring to FIG. 1, for example, a television signal processing circuit 10 including a video detector supplies a demodulator-matrix 12 with luminance (Y) and chroma (C) signal components to provide a similar video drive amplifier (FIG. Color video signals B, R and G (i.e., blue, red and green video display signals) are supplied to 20a), 20b and 20c. The amplified video output signals are respectively supplied from the respective amplifiers 20a, 20b and 20c to the respective sensitivity control cathode electrodes 42a, 42b of the color image reproduction kinescope 44 of the in-line gun, and It is supplied to 42c.

Since the amplifiers 20a, 20b, and 20c are identical, only the amplifier 20a and its associated circuits will be described in detail.

The video amplifier 20a includes a cascade array of a common emitter transistor 22 and a common base transistor 23. The emitter of transistor 22 is coupled to an operating reference power supply 30 that includes transistor 31 through resistor 24. The potential supply 30 supplies the operating reference potential for the video amplifiers 20b and 20c. The collector output of the common base transistor 23 is operated via the collector-emitter current path of the emitter follower transistor 28 and the load resistor 25 which supply a low impedance control voltage from the emitter electrode described below. Is bound to (B ⁺ ).

The common emitter transistor 22 and the base supply the video signal B from the demodulator-metrics 12, and the amplified signal of the signal C appears at the collector output of the transistor 23. This signal is a DC coupled to the B signal cathode 42a of the kinescope 44 via a diode 38 in the current sensing circuit 40a. In this example, the kinescope 44 is in the form of an in-line gun as a conventional active grid 45 associated with each electrode gun including the cathode electrodes 42a, 42b and 42c. The grid 45 is suitably biased from a fixed power supply of positive DC potential + V ₂ (eg, + 20V).

The current sensing circuit 40a is used as an optical coupling circuit and includes a light emitting diode (LED) optically coupled to the photosensitive diode 39 biased from a direct current source (in this case B ⁺ ). The diode 38 is in the cathode current Ik path between the cathode 42a and the collector output of the transistor 23. The output of the diode 39 is coupled to the bias) control circuit.

The bias control circuit 50a includes a pair of transistors 52 and 54 that are keyed and low voltage differentially connected, a filter circuit 62 and a full voltage emitter follower transistor 28. The base electrode of the transistor 54 is held at a fixed bias (e.g., + 210V) supplied from the reference electrode 53, and the bias supplied to the base electrode of the transistor 52 from the output of the sensing circuit 40a is In operation, it changes in accordance with the conduction of the diode 39, which changes according to the current conduction of the diode 38. The operating reference voltages for the differential transistors 52 and 54 are supplied from a voltage source comprising transistors 58 and resistors 55 arranged as shown. Transistor 58, transistor 52, and transistor 54 are keyed to conduct in response to a periodic bypass keying pulse supplied from source 60.

In this example, the keying pulses occur during each horizontal blanking period, at which time the video information does not appear in the video signal. During this time, differential amplifiers 52 and 54 sense the current flowing through diode 39 (this current is proportional to the cathode current I _K flowing through diode 38) and passes through diode 38. A control voltage is provided to the collector output of transistor 54 in proportion to the current. The current sensed corresponding to the cathode current I _K level appears during this blanking period and can therefore be referred to as the cathode blanking current. This control voltage is filtered by the parallel coupling of the resistor 61 and the filter capacitor 63 forming the circuit 62. The filtered control punch pressure appears at both ends of the capacitor 63 and is coupled to the base attraction force of the follower transistor 28. This control voltage appears on the emitter of transistor 28 (reduced by the base-emitter junction drop of transistor 28) and changes the constant current through load resistor 25 and the collector voltage of transistor 23. .

The video drive amplifiers 20b and 20c have associated sensing circuits 40b and 40c and bias control circuits 50b and 50c, respectively. These circuits are arranged and operate in the same manner as the control circuit 30a and the sense channel 40a associated with the amplifier 20a. Therefore, the following description of the operation of the automatic kinescope bias control circuit associated with the video amplifier 20a and the signal B also applies to the amplifiers 20b, 20c and the associated R and G cathode signals.

Under steady state, the system shown in FIG. 1 is designed to provide a given cathode ranking current. In particular, signal blanking in which signal processing is included in stage 10 and the signal processing circuits associated therewith is such that the kinescope 44 conducts a small amount of cathodes (e.g., about 5 ms) during each horizontal blanking period. Are arranged. This can be done, for example, by arranging the signal blanking circuit in stage 10 such that the blanking signals generated by these circuits do not completely block the input signal to the driver 20a during the horizontal blanking period. In this method, a small amount of current will be conducted by the video driver stage 20a during the horizontal blanking period and this small amount of current matches the cathode blanking current sensed by the circuit 40a and is visible in the reproduced image. Makes it ineffective. The normal collector voltage of the video output transistor 23 represents the operating voltage of the cathode 42a. During the horizontal blanking period, this collector voltage causes a given level of cathode blanking current to the grid voltage of the B signal electron gun of the kinescope 44.

The light emitting diode 38 in the sensing channel 40a senses the cathode blanking current and emits an amount of light proportional to the cathode blanking current. Light emission of the diode 38 is sensed by an optically coupled photosensitive diode 39 that is electrically isolated from the diode 38 and the cathode current path. The current induced in the diode 39 then is keyed to cause the current source transistor 58 to conduct during the blanking period already described, thus providing a given amount of base current to drive the differential transistor 52 to be conducted at this time. In this example, the differential amplifier circuit comprising transistors 52 and 54 is designed so that the current supplied from the source 58 under a steady state makes a given collector voltage of the transistor 54 during this state (the current decomposition method is Otherwise selected), it is arranged to distribute evenly between the emitters of transistors 52 and 54.

The filtered voltage of this collector voltage appears across the capacitor 63 at the junction of the capacitor 63 and the resistor 61. Resistor 61 causes the filtered voltage to appear at the average level after the initial minority keying cycle for a given cathode current level. This resistor also results in a controlled loop gain that includes circuit 50a. The time constants (eg, 100 ms) of the filter circuits 61 and 63 are selected such that the filtered voltage is held on the capacitor 63 for the period of the horizontal image period in this example. The filtered voltage also appears at the base of transistor 28 and the proportional voltage appears at the emitter of transistor 28. (Ie, the base voltage is less than the base-emitter junction voltage drop of transistor 28). The normal collector output voltage of transistor 23 corresponds to the emitter voltage of transistor 28 shown as discussed less than the voltage drop across load resistor 25.

If the cathode blanking current deviates from the normally expected level (e.g. due to long-term etching of the kinescope or a change in the operating characteristics of the kinescope 44), the collector voltage of the video output transistor 23 is uneven. It is controlled to change in the direction to compensate. In other words, the collector voltage of the transistor 23 is changed in a direction such that the difference corresponding to the normal and desirable blanking level of the cathode current Ik is to maintain the cathode-to-grid voltage.

For example, as the cathode blanking current increases, diode 38 conducts an additional current such that increased light emission is sensed by diode 39. The conduction of the diode 39 increases by a corresponding amount, thereby supplying an additional base current for driving the differential transistor 52. When the transistors 52 and 54 are brought into conduction during the keying (blanking) period, the collector voltage of the transistor 54 is increased above the normal collector voltage level by a differential operation.

Thus, the filtered voltage appearing at the base of the capacitor 63 and the transistor 28 increases by a proportional amount, causing the emitter voltage of the transistor 28 and the collector voltage of the output transistor 23 to increase in operation. This increased collector voltage is of magnitude and direction that reduces the cathode blanking current toward the normal level. This reduced cathode blanking current is achieved by correspondingly reducing the collector load constant current of transistor 23. The emitter current of transistor 23 remains unchanged because it is determined by the current supplied by source 30.

The above considerations also apply when the cathode blanking current decreases below the normal level in the " blacker-than-black " direction. In this case, the collector voltage of the transistor 23 is reduced by the compensation amount.

The control arrangement described applies a control voltage to the low impedance through the emitter of the transistor 28, so that the collector constant current of the transistor 23 and the voltage of the transistor 23 couple from the collector of the transistor 23 to the cathode 42a. It is very unusual because the controlled video signal and the control voltage do not interact with each other and are controlled in such a way as to preserve the desired normal blanking level of the cathode current (i.e., this control path is isolated from the cathode video signal path). Using an optically coupled sensing circuit 40a has the advantage that the circuit electrically insulates the cathode current path from the control circuit 50a. In addition, the sensing circuit 40a and the control circuit 50a (which may exclude the filter capacitor 63) may be formed as an integrated circuit. In practice, it is impossible to manufacture a high voltage transistor of the video driver 20a in an integrated circuit, but the recent integrated circuit technology believes that such a high-voltage transistor can be integrated in the near future. In this case, the entire video driver stage including the automatic bias control circuit can be formed in the form of a single monolithic integrated circuit.

The arrangement of FIG. 2 is the same as that of FIG. 1 except that the filter circuit 62 is changed.

In FIG. 2, a control voltage indicating the blanking level of the cathode current Ik shown at the transistor 54 and collector output is applied to the filter capacitor 63 via the keyed electronic switch 64. As shown in FIG. The keying pulse supplied to the switch 64 from the source 60 (FIG. 1) causes the switch 64 to be closed for each period if desired to sample the cathode blanking current, and the resistor 61 and the transistor. The charge storage capacitor 63 is opened at another time to separate it from the collector of 54. In this example, the keying pulse is applied to the switch 64 rather than the current source transistor 58 as shown in FIG. The special arrangement of this circuit 62, except for the negligible base current induced by the transistor 28, because the charge accumulated on the capacitor 63 is maintained without consumption during the sampling period, the arrangement of FIG. Corresponding to a sample and sustain circuit which provides a more accurate control voltage to the transistor 28 as compared to. This sample and hold circuit comprising a capacitor 63 and a switch 64 can be made according to the differential sample and hold circuit described in US Pat. No. 3,740,456, for example.

The arrangement of FIG. 3 is the same as that of FIG. 1 except that a different cathode current sensing arrangement is used.

Except as described below, the circuit of FIG. 3 is the same as FIG.

In FIG. 3, the cathode blanking current is sensed by the sense resistor 340 arranged in series from the cathode 42a to the collector of the transistor 23. The control circuit 350 includes a differential amplifier comprising a filter circuit 62 and a transistor 28 (as shown in FIG. 1), differentially connected high voltage transistors 352 and 354, and transistors 352 and 354. And a current source comprising a high voltage NDN transistor 358 coupled to a coupled emitter of < RTI ID = 0.0 > In this embodiment, forward keying pulses are used to key the current source transistor 358 during the previously described blanking period.

Base input electrodes of transistors 352 and 354 are coupled across the resistor 340 to sense the differential voltage present in resistor 340 in response to the level of the cathode blanking current.

The control voltage shown on the collector of transistor 352 during the keying period is filtered by capacitor 63 and coupled to the collector of transistor 23 through transistor 28.

As the cathode blanking current increases beyond the normal level and out of the normal level, the end of the resistor 340 far from the collector of the transistor 23 becomes more positive than normal.

During the keying period, the collector voltage of the transistor 352 increases by a proportional amount by the differential operation of the transistors 352 and 354, so that the cathode blanking current is directed toward the normal level as discussed with reference to FIG. In order to decrease, the collector voltage of the transistor 23 increases.

In the embodiment shown in FIG. 4, the output current from the sensing circuit 40a (i.e., the current from the diode 39 in FIG. 1) supplies the base current to the transistor 410 to control the current conduction state. . Transistor 410 attempts to conduct when current-wind transistor 58 is keyed to conduct as described with reference to FIG. 1, and filter circuit 62 coupled to the collector output of transistor 410 is shown in FIG. It is used for the same purpose as described for arrays. According to the magnitude of the sensed cathode blanking current, the filtered control voltage shown on the collector of the transistor 410 controls the current conduction state of the transistor 412 from the normal conduction level, thereby reducing the collector and voltage current of the video output transistor 23. It is used to control. Transistor 412 and its associated emitter resistor 418 represent a current source coupled between the collector output of transistor 23 and ground.

When the cathode blanking current deviates from the normal value in the forward direction, for example, the base current supplied to the transistor 410 from the output of the sensing circuit 40a is increased, thereby reducing the current conduction state and the collector voltage of the transistor 410. Increase and decrease respectively. In operation, the reduced collector voltage of transistor 410 increases and decreases the collector voltage and current conduction state of current source transistor 412, respectively. This operation causes the collector voltage and current of the amplifier transistor 23 to increase and decrease by a corresponding amount, respectively, so that the cathode blanking current decreases toward the normal blanking level.

Although the present invention has been described only for the specific embodiments, it can be variously changed within the scope of the present invention.

For example, the bias control voltage can be used to control the output operating voltage of the video driver in a system in which the driver applies amplified video signals to each individual control grid associated with each electron gun of the kinescope. In this case, it can be used to controllably indicate the operating voltages of the individual grid electrodes instead of the respective cathode voltages as in the embodiment describing the output driver voltage of the video driver.

The cathode current can be sensed for a different period of time than described, depending on the requirements of the special system.

For example, the cathode current can be sensed during the first fractional scan line after each vertical retrace period. Examples of this detection technique include "Permanent Color Purity" by I. A. Jensen (published by Bang & Orufsen, Denmark) and "Automatic Color Scheme in Color TV Receivers" by P. J. and Asch Jensen. Stabilization "(IEEE February 1977). With this technique, the video signal is separated and a local reference voltage is used during the measurement period to induce the cathode blanking current. The deviation of this cathode current from the expected level is sensed and compensated by the associated control circuit. At this time, since the kinescope detecting the cathode current is overscanned, there is no visible effect on the displayed image (that is, the kinescope electron beam is deflected to impinge the kinescope surface on the image region).

Claims (1)

An image display video signal processing application device in which an image period and a blanking period occur periodically, and a video reproduction kinescope device having a sensitivity control transfer and a video signal finally amplified from the output of the video amplifier to the kinescope transfer. A video signal processing apparatus comprising a video amplifier for a signal amplifier, an operating circuit and an output circuit for an amplifier coupled between the operating panel and the amplifier output and having a load impedance, the magnitude of the current conducted by the kinescope current. A device for detecting a signal, a device coupled to the device for generating a control voltage representing a current deviation of the current from a reference level during a blanking period, and supplying the control voltage to an output circuit to separate the amplifier from the video signal. By changing the constant current through the load impedance and constant voltage at the output, The desired probe of automatic kinescope control circuit, characterized in that the device to minimize the difference between the sensed current and the ranking probe current ranking.

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