US3714502A - Circuit for controlling an intensity of a scanning in an electromagnetic deflection type cathode ray tube - Google Patents

Circuit for controlling an intensity of a scanning in an electromagnetic deflection type cathode ray tube Download PDF

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Publication number
US3714502A
US3714502A US00046611A US3714502DA US3714502A US 3714502 A US3714502 A US 3714502A US 00046611 A US00046611 A US 00046611A US 3714502D A US3714502D A US 3714502DA US 3714502 A US3714502 A US 3714502A
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United States
Prior art keywords
circuit
deflection coil
ray tube
cathode ray
intensity
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Expired - Lifetime
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US00046611A
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English (en)
Inventor
K Hirayama
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Iwatsu Electric Co Ltd
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Iwatsu Electric Co Ltd
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Priority claimed from JP4683369A external-priority patent/JPS492845B1/ja
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R13/00—Arrangements for displaying electric variables or waveforms
    • G01R13/20—Cathode-ray oscilloscopes
    • G01R13/22—Circuits therefor
    • G01R13/26—Circuits for controlling the intensity of the electron beam or the colour of the display
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
    • H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
    • H04N3/16—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by deflecting electron beam in cathode-ray tube, e.g. scanning corrections
    • H04N3/20—Prevention of damage to cathode-ray tubes in the event of failure of scanning

Definitions

  • ABSTRACT A circuit for controlling an intensity of a scanning in an electromagnetic deflection type cathode ray tube generates an unblanking pulse only when a current change exists in a deflection coil of the cathode ray tube.
  • the unblanking pulse is applied to an intensity modulation grid of the cathode ray tube thereby a fluorescent surface is maintained in an unblanking condition when the current change exists in a deflection coil and in a blanking condition when no current change exists in a deflection coil.
  • SHEET 30F 5 9 5 ICE L CIRCUIT If) (POSITIVE) SIDE (J') OR II SLIcE A CIRCUIT i N ATIv bf) 5 DIEEERENTIAL FROM vERTIcAL OPERATIONAL DEFLECTION cOIL AMPLIFIER (k) (U AND I5 I14 CONSTANT CRT TIME HOLD INTENSITY -TO CRT cIRcuIT MODULATION AMPLIFIER PULSE SHAPER INTENSITY MODULATION SIGNAL PATENTED JAN 3 0 I975 SHEET 4 BF 5 PATENTEUJAIISO 1915 3,714,502
  • the present invention relates to a circuit for controlling the brightness of a brightening spot displayed in an electromagnetic deflection type CRT by detecting the scanning velocity of an electron beam, thereby maintaining the brightening spot at a constant brightness independent of the scanning velocity and preventing a burning of a fluorescent surface of CRT in the event the spot is fixed to a certain position due to the cause of some unknown or undetectable cause.
  • the conventional electromagnetic deflection type CRT a displayed figure is maintained to a constant brightness by classifying the brightness signals to several kinds of levels corresponding to several sweeping velocities at a control section where an analog signal is supplied to a CRT deflection system and using them as brightness signals.
  • the conventional circuits used for protecting the tube from a burning are as follows. When the sweeping is not carried out in an oscillograph, a trigger signal has been used for extinguishing the brightness of a spot. Also, when the sweeping stops by turning of a power switch of an apparatus, such as a television receiver, the burning protection method of swinging the brightening spot, by using a blocking oscillator, has been used during the time between the stopping of the scanning and the anode voltage.
  • the means of controlling the brightness of the brightening spot has been selected independent of the change rate of the current (or voltage) in the CRT indicating device, so there have been some problems in protecting the fluorescent surface from damage by extinguishing the brightness of the brightening spot perfectly.
  • the object of the present invention is to provide a circuit for controlling the brightness of the brightening spot by detecting the sweep velocity of the analog signal applied without burdening the above-mentioned control section thereby keeping constant brightness independent of the sweep velocity.
  • Another object of the present invention is to provide a circuit which can protect the fluorescent surface from damage, controlling the brightness of the spot by direct detection of the current change rate in the deflection coil by producing an unblanking pulse from the positive change of the current change rate in the deflection coil and by producing an unblanking pulse from a negative change of the current change rate above-mentioned, thereby establishing a condition in which the brightening spot on a CRT fluorescent surface is produced only when the above-mentioned current change exists in the deflection coil, and effecting a blanking condition when the current change in said deflection coil is stopped, thereby extinguishing the brightness spot when the brightness spot is fixed due to any condition.
  • a further object of the present invention is to provided a circuit for controlling the brightening spot of a scanning system such that of an oscilloscope and television apparatus, especially in the graphic display apparatus due to the random positioning system.
  • FIG. I is a block diagram of the principle of the present invention.
  • FIG. 2 is a block diagram of one embodiment of the present invention
  • FIG. 3 is a detailed circuit diagram of FIG. 2,
  • FIGS. 4A and 4B are circuit diagrams showing one example of a function generator of FIG. 2,
  • FIG. 5 is a block diagram of another embodiment of the present invention.
  • FIG. 6 is an explanatory diagram showing waveforms at various portions in FIG. 5,
  • FIG. 7 is a circuit diagram of another example of the present invention.
  • resistor R is connected in series with a deflection coil composed of an inductance L and a DC resistance R and the other end of this resistor is grounded. Both ends of the deflection coil are connected, through resistor R and R respectively, to the two input terminals of the operational amplifier l, the junction point of resistor R, and an input terminal of the operational amplifier 1 is grounded through resistor R the output terminal of the operational amplifier 1 is, through resistor R connected to the junction point of resistor R and the other input terminal of the operational amplifier 1.
  • the voltages E and E at both terminals of the deflection coil are represented as follows:
  • V detecting circuit 2 and V detecting circuit 3 are connected to horizontal deflection coil L and vertical deflection coil L respectively, and detect the terminal voltage of each deflection coil L or Ly.
  • the above-mentioned V detecting circuit 2 and V detecting circuit 3 are connected to (V V operational circuit 4 and further, through the function generator 5, connected to the intensity modulation amplifier 6.
  • blanking and unblanking signals are connected from externally to the intensity modulation amplifier 6. And only when the unblanking pulse is applied, the output of the intensity modulation amplifier can be applied to the intensity modulation grid of the CRT.
  • FIG. 3 shows an actual example of (V V operational circuit 4. ln connection with this, the circuit comprising transistors 0,, Q Q Q and Q, is a type of differential amplifier. Now, the positive or negative signal V is applied to the input terminal of the above-mentioned differential amplifier. The emitter follower outputs of transistors Q, and Q, are combined and converted through diodes D and D into the signal of the same polarity. The output at the junction point of diodes D, and D is amplified by transistor Q and applied to the field effect transistor 0,. As it is possible to give square law detection characteristics between gate voltage and drain current of the field effect transistor 0,, so V proportional to the square of V is obtained as an output of field transistor It is possible to obtain the output V V i.e. VJ by adding both V and output V of the circuit which calculate V (this is the same as the V and therefore, it is not shown in the drawing) using output voltage V of Y-axis in the operational amplifier 7.
  • FIGS. 4A and 4B shows an example of the function generator.
  • the brightness of beam B has the following relation, assuming the brightening spot area is constant.
  • V0 is the cut-off voltage of intensity modulation grid
  • Vd is the intensity modulation grid voltage taking V0 as a reference voltage.
  • the deflection velocity of the beam is VsadI /dt (l0) where 1,, is the deflection coil current. Furthermore, putting V as the terminal voltage of the deflection coil, then dI /dta V (1 l) From Eqs. (7) (11), the relation of V and Vd which keeps the brightness of beam constant is obtained. For example, in the electromagnetic deflection for TV described herein, putting P 4/5 in Eq. (7), then a functional relation of Vda VL5I14 On the other hand, since 1. VLX2 VLY2 we have Vda( V W (14) Although the index 5/14 in Eq.
  • FIG. 5 shows another embodiment of the present invention. That is, the circuit referring to FIG. 5 is an example of the fluorescent surface burning protection circuit. Referring to FIG. 5, the explanation is given for the electromagnetic deflection CRT, however, the same explanation is applied to the case of the electrostatic deflection system.
  • the displacement of the brightening spot on the fluorescent surface of CRT depends on the flux change in the deflection coil, i.e. the deflection coil current change. Therefore, in order to prevent damage of the fluorescent substance of the CRT fluorescent surface, when the deflection coil current change is stopped, it may be well to change the condition of the CRT fluorescent surface into the blanking condition. In other words, it may be well to produce the unblanking signal only when the deflection coil current changes.
  • FIG. 5 is shown in the case of the horizontal defection coil. However, in the case of the vertical deflection coil, its operation principle is the same, then its explanation will be omitted.
  • FIG. 6 shows the waveform at several locations in FIG. 5.
  • the unblanking pulse due to the vertical coil current change is, together with the abovementioned unblanking pulse due to the horizontal deflection coil current, applied, through the OR circuit 11 to a constant time hold circuit 12.
  • the constant time hold circuit 12 is represented by a dotted line C in FIG. 7, and its capacitor C, is charged with low impedance through the OR circuit 11 in a charging condition, and discharged with a comparatively high impedance through comparatively high resistors R and R, in a discharging condition. Accordingly, the waveform at point (K) becomes as shown in FIG. 6(k). Slicing this waveform at some level and inversing its phase, its waveform becomes FIG. 6(1).
  • We can achieve the desired object by adding the logical product of this waveform as the intensity modulation signal to the intensity modulation circuit of CRT.
  • the voltage between the base and emitter of transistor O is the potential difference between waveforms (c) and (d), i.e. this is the potential difference of waveforms (a) and (b). In other words, this is the voltage proportional to the current change rate dI/dt.
  • Transistor Q detects this potential difference and the waveform at the collector of O is as shown in FIG. 6(e).
  • Transistor 0, shapes this waveform (e) and applies it to transistor 0,, and the waveform (f) in FIG. 6 appears at the output of the emitter follower transistor 0,
  • the above circuit which comprises transistors 0 Q,,, Q,,,, 0,, and 0, detects the positive change rate of the deflection coil current.
  • the negative change rate of the deflection coil current is detected by the circuit comprising transistors Q,,, 0, 0, 0, 0,, and 0,
  • the phases of the waveforms (e) and (i) at the collectors of transistors Q and Q are inverse, respectively.
  • the phases at the points of (f) and (j) become concurrent.
  • the unblanking pulse due to the vertical coil current change rate also, together with the above-mentioned unblanking pulse due to the horizontal coil current change rate, charge capacitor C, through diodes D and D,,.
  • charge capacitor C is quite the same as in the case of FIG. 5, and therefore, will be omitted here.
  • Circuitry for controlling the intensity of a brightening spot during scanning of an electromagnetic deflection type cathode ray tube comprising a deflection coil circuit for a cathode ray tube, means coupled to said deflection coil circuit for generating a voltage V proportional to the current change rate dI/dt in said deflection coil circuit, function generator means coupled to said V, generating means for generating a voltage Vd having a value which increases exponentially with respect to V and means coupled to said function generator means for applying a voltage Vd proportional to an intensity modulation grid of the cathode ray tube, thereby maintaining the brightening spot at a constant intensity during scanning of the cathode ray tube.
  • a circuit for use in controlling the intensity of scanning in an electromagnetic deflection type CRT, said CRT having a deflection coil and an intensity modulation grid said circuit comprising, means for detecting a voltage V proportional to a sweep current change rate dI/dt in a deflection coil of a CRT between terminals of said deflection coil, an operational amplifi-' er, said means for detecting said voltage comprising a resistor R connected to one terminal of said deflection coil having a DC resistance R' and ground resistors R and R respectively, connected to terminals of said deflection coil and input terminals of said operational amplifier, a resister R connected between one input terminal of said operational amplifier and ground, a resistor R connected between an output terminal of said operational amplifier and the other input terminal of said operational amplifier, and the following relation existing between the resistance values of said resistors R, R, R,, R R and R Where R R means for generating an unblanking pulse, means for applying the output of said operational amplifier to said means for generating an
  • a circuit for use in controlling the intensity of scanning in an electromagnetic deflection type cathode ray tube wherein said means for generating an unblanking pulse is composed of a first slice circuit means for slicing said positive voltage and a second circuit means for slicing said negative voltage connected in parallel, means connecting said first and second slice circuit means to said output of said operational amplifier, means connecting outputs of said first slice circuit and said second slice circuit each to a different input terminal of an OR circuit, an OR circuit receptive of said outputs of said first slice circuit means and second slice circuit means applying them to a constant time hold circuit, a constant time hold circuit provided with a capacitor charged at low impedance through said OR circuit and discharged at a comparatively high impedance, a pulse shaper receptive of the output of said constant time hold circuit and shaping it, an intensity modulation smplifier, means applying the output of said pulse shaper applied via said intensity modulation amplifier to the intensity modulating grid of said electromagnetic deflection type CRT.
  • a circuit for use in controlling the intensity of scanning in an electromagnetic deflection type CRT, said CRT having a deflection coil and an intensity modulation grid said circuit comprising, means for detecting a voltage V proportional to a sweep current change rate dI/dt in a deflection coil of a CRT between terminals of said deflection coil, said means for detecting said voltage comprising a resistor R connected to one terminal of said deflection coil and to ground, a first amplifier, a second amplifier, a third amplifier and a fourth amplifier, one terminal of said deflection coil being connected to the first and second amplifiers, the other terminal of said deflection coil being connected to the third and fourth amplifiers, said first and third amplifiers being provided for amplifying a positive voltage, said second and fourth amplifiers being provided for amplifying a negative voltage, first slice circuit means for slicing said positive voltage, second slice circuit means for slicing said negative voltage, means connecting a difference output between said first and third amplifiers to said first slice circuit means for s

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Details Of Television Scanning (AREA)
  • Transforming Electric Information Into Light Information (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
US00046611A 1969-06-16 1970-06-16 Circuit for controlling an intensity of a scanning in an electromagnetic deflection type cathode ray tube Expired - Lifetime US3714502A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP4683369A JPS492845B1 (enrdf_load_stackoverflow) 1969-06-16 1969-06-16
JP6038169 1969-08-01

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DE (1) DE2029805B2 (enrdf_load_stackoverflow)
GB (1) GB1311763A (enrdf_load_stackoverflow)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3831057A (en) * 1972-02-28 1974-08-20 Licentia Gmbh Circuit arrangement for generating a beam current in a cathode-ray tube
DE2558265A1 (de) * 1974-12-23 1976-07-01 United Technologies Corp Einrichtung zum schutz des leuchtschirms einer katodenstrahlroehre vor beschaedigung
EP0258849A3 (en) * 1986-09-02 1990-11-28 Tektronix, Inc. Xy display transition intensifier

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3004187A (en) * 1960-02-11 1961-10-10 Hughes Aircraft Co Cathode ray tube intensity control system
US3191090A (en) * 1962-07-17 1965-06-22 Hughes Aircraft Co Electron beam uniform intensity control circuit
US3325803A (en) * 1964-10-01 1967-06-13 Ibm Deflection control circuit
US3502937A (en) * 1968-11-12 1970-03-24 Minnesota Mining & Mfg Electron beam image intensity control

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3004187A (en) * 1960-02-11 1961-10-10 Hughes Aircraft Co Cathode ray tube intensity control system
US3191090A (en) * 1962-07-17 1965-06-22 Hughes Aircraft Co Electron beam uniform intensity control circuit
US3325803A (en) * 1964-10-01 1967-06-13 Ibm Deflection control circuit
US3502937A (en) * 1968-11-12 1970-03-24 Minnesota Mining & Mfg Electron beam image intensity control

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3831057A (en) * 1972-02-28 1974-08-20 Licentia Gmbh Circuit arrangement for generating a beam current in a cathode-ray tube
DE2558265A1 (de) * 1974-12-23 1976-07-01 United Technologies Corp Einrichtung zum schutz des leuchtschirms einer katodenstrahlroehre vor beschaedigung
EP0258849A3 (en) * 1986-09-02 1990-11-28 Tektronix, Inc. Xy display transition intensifier

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GB1311763A (en) 1973-03-28
DE2029805A1 (enrdf_load_stackoverflow) 1971-02-04
DE2029805B2 (de) 1972-02-24

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