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

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. As a result of this, an intensisty of a scanning can be in constant brightness independent of the scanning velocity and further, a burning of the fluorescent surface of the cathode ray tube can be prevented in case movement of a brightness spot is stopped.

Description

ite States Patent 1191 Hirayama 1 1 Jan. 30, 1973 541 CIRCUIT FOR CONTROLLING AN 3,004,187 10/1961 015011 ..315 22 INTENSITY ()F A SCANNING IN AN 3,325,803 6/1967 Carlock etal. ..31s 1s x 4 3,191,090 6/1965 Vittetal. ..31s 22 ELECTROMAGNETIC DEFLECTION TYPE CATHODE RAY TUBE [75] Inventor: Kazuhiro Hirayama, Tokyo, Japan [73] Assignee: lwatsu Electric Company Limited,

Tokyo, Japan [22] Filed: June 16, 1970 [Zl] Appl. No.: 46,611

[30] Foreign Application Priority Data June 16, i969 Japan ..44/46833 Aug. 1, 1969 Japan ..44/6038l [52] U.S.Cl ..315/30,3l5/22 [51] Int. Cl. ..ll01j 29/52 [58] Field of Search ..3 15/30, 27 TD, 18,22 R, 22

[56] References Cited UNITED STATES PATENTS 3,502,937 3/1970 Bader et al. ..3l5/3O Primary Examiner-Carl D. Quarforth Assistant Examiner-J. M. Potenza AttorneyRobert E. Burns and Emmanuel J. Lobato [57] 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. As a result of this, an intensisty of a scanning can be in constant brightness independent of the scanning velocity and further, a burning of the fluorescent surface of the cathode ray tube can be prevented in case movement of a brightness spot is stopped.

4 Claims, 8 Drawing Figures 2 VLX LX DETECTING TVLX CIRCUIT 4 5 d 2 RX dh E RZTTYo N A VZL FUNCTION L GENERATOR- 3 W CIRCUIT L VLY DETECTING a CIRCUIT 'NTENS'TY TO INTENSITY MODULATION- MODULATION i AMPUFIER RY VL|4 can) OF @1 11 SIGNAL PATENTEUJAN 3 0 i973 SHEET 10F 5 DEFLECTION COIL J2 VLX L DETECTING VLX CIRCUIT 5 d 2 T RX O E RT I O III A E FUNCTION L G NERATOR 3 W cIRcuIT E L VLY DETECTING -63 CIRCUIT 'NTENSITY TO INTENSITY MODULATION MODULATION i AMPLIFIER RY VLI4 GRID OF CRT BLANK'NG/UNBLANKING SIGNAL PAIENTEIIJAIIBO I975 3,714,502

SHEET 2 OF 5 OPERATIONAL AMPLIFIER MM 8 l U OPERATIONAL AMPLIFIER PATENTEDJI'IHO I975 3,714,502

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

sum 5 BF 5 FROM VERTICAL DEF LECTI ON COI I.

DEF ELECTION COI L L I HORIZONTALI TO INTENSITY MODULATION GRID OF CRT CIRCUIT FOR CONTROLLING AN INTENSITY OF A SCANNING IN AN ELECTROMAGNETIC DEFLECTION TYPE CATHODE RAY TUBE 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.

In 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. Further, 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. However, in the cases of the above-mentioned two methods, 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.

Other features and advantage of the present invention will be apparent from the ensuing description with reference to the accompanying drawing to which, however, the scope of the invention is in no way limited.

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.

Referring to FIG. 1, in a detecting circuit of th 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. In the circuit connected like this, the voltages E and E at both terminals of the deflection coil are represented as follows:

Next, to perform the calculation of Eq. (3), we examine the relation of the values of resistors R R R and R in the operational amplifier 1 and the output voltage E0 is given by the following equation:

12.41; i Y R3 R.+R. 1 RQ (4) Putting R1=R3, then & M E. R. R1+R2 m (5) For Eq. (5) represents Eq. (3), the following relation must be satisfied.

R R R I R+ R (1.3+ R. 5 R3) Namely, when Eq. (6) is satisfied, then EoaL and by using R and the above-mentioned operational amplifier I, eliminating the voltage rising due to the DC resistor R in the deflection coil, and detection of dI /dt can be obtained correctly.

Referring to FIG. 2, horizontal deflection coil L, and vertical deflection coil Ly are grounded through resistors R and Ry, respectively. And 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. On the other hand, 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.

In general, in a CRT, the brightness of beam B has the following relation, assuming the brightening spot area is constant.

Pa)P/ s (7) where I is the 3rd plate current, V is the sweeping velocity of the beam and the value of P, depending on the fluorescent substance, lies between 0.7 and 0.9.

Furthermore, in an electromagnetic deflection type CRT for general TV is P3 I K where I is the cathode current of the CRT. This current is expressed by the following equation:

I, a Vd' /V0 In Eq. (9), V0 is the cut-off voltage of intensity modulation grid, Vd is the intensity modulation grid voltage taking V0 as a reference voltage.

On the other hand, 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. (13) is somewhat variable corresponding to the types of CRT, it remains always to be as a monotone increasing function. Therefore, as in the circuit shown in FIG. 4A, adjusting the values of resistors properly, an arbitrary monotonous increasing function approximate to the curve denoted in Eq. (13) or (14), as shown in FIG. 48, can be obtained.

In this invention, as above-explained, it is possible to maintain the brightness constant independent of the sweeping velocity by obtaining an output proportional to Vd which satisfies the relation in Eq. (13), as an unblanking level of the intensity modulation signal, and supplying this from the intensity modulator to the intensity modulation grid of the CRT and controlling the brightness of the brightening spot.

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.

In FIG. 5, assuming the deflection coil inductance is L, and its DC resistance R, the following explanation is given. The resistor R connected in series with the above L and R is provided for detecting the coil current. If deflection coil current is I, the voltages of both ends are E,, E and the output voltage of the differential operational amplifier is E0, then the following equations are obtained from Eq. (6).

when Eq. (15) is satisfied, we obtain EoaL dI/dt Thus, we can detect the current change rate dI/dt eliminated the voltage drop due to the DC resistance in the deflection coil. Namely, supplying the deflection current waveform as shown in FIG. 6(a) and the voltage waveform of the deflection coil as shown in FIG. 6(b) to the input circuits in FIG. 5, the resultant waveform of hatching parts of FIGS. 6(c) and (g) appears at the output terminal of the operational amplifier I. The positive side of the output wave in the abovementioned operational amplifier is shaped in the positive side slice circuit 9 (corresponding to the location A in FIG. 7) and the waveform appearing at its output terminal corresponds to FIG. 6( and furthermore, applied to an OR circuit 11. Quite similarly, the negative side of the output wave in the above-mentioned operational amplifier 1 is shaped in the negative side slice circuit (corresponding to the location B in FIG. 7) and the waveform appearing at its output terminal corresponds to FIG. 6( and furthermore, applied to an OR circuit 11.

Also, similarly, 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.

By the method described in FIG. 5, we can detect the deflection coil current change dI/dt correctly by using the differential type operational amplifier 1, but when the DC resistance in the deflection coil is negligible, we can perform the circuit construction by using simpler components as shown in FIG. 7. When the deflection voltage waveform (b) in FIG. 6 is applied to the input terminal (b) in FIG. 7, the waveform (a) in FIG. 6 appears at the junction point of the deflection coil L and the series resistor R. Waveforms (a) and (b) are applied to PNP transistors Q and 0, respectively, and emitter follower output waves (c) and (d) of transistors Q, and 0, are applied differentially to the base and emitter of transistor 0,, respectively. Namely, 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. Similarly, the negative change rate of the deflection coil current is detected by the circuit comprising transistors Q,,, 0, 0, 0, 0,, and 0, In this case, the phases of the waveforms (e) and (i) at the collectors of transistors Q and Q, are inverse, respectively. However, after passing through the phase inverse circuit 0, the phases at the points of (f) and (j) become concurrent. Again, similarly, 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,,. As the operation after capacitor C, is quite the same as in the case of FIG. 5, and therefore, will be omitted here. From the above-mentioned explanation, it is clear that the feature of the circuit shown in FIGS. 5 and 7 are by correctly detecting the current change rate dI/dt in the deflection coil and producing the unblanking pulse and keeping it under the condition so as being capable of producing a brightness spot on the fluorescent surface of CRT, and when the current change rate dI/dt become zero, it is possible to protect the damage on the fluorescent surface even when the spot is located at any point on the CRT fluorescent surface. Next, as condenser C, is charged with a low impedance and discharged with a comparatively high impedance, when the spot begins to move from the stop position, the signal changes as shown in FIG. 6(l from the blanking state to the unblanking state with a considerably short time lag and the gate for the Z signal is opened. Also, when the spot, from the state of moving, stops, as the discharge of C, is performed with a comparatively long time constant C,(R R,), the gate for the Z signal is opened for a period of time after the spot is stopped. This fact is well-fitted to the operation of such a CRT display apparatus due to the random positioning, especially, to satisfy the required conditions for such a program.

Modifications of the herein disclosed circuits will occur to those skilled in the art and various combinations of the circuits will be capable of use together for achieving the desired results of the invention. The

scope of the invention is to be interpreted accordingly as defined by the appended claims.

What I claim and desire to secure by Letters Patent l. 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.

2. 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 unblanking pulse, means receptive of the output of said means for generating an unblanking pulse applying it to the intensity modulation grid of said electromagnetic deflection type cathode ray tube.

3. A circuit for use in controlling the intensity of scanning in an electromagnetic deflection type cathode ray tube according to claim 2, 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.

4. 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 slicing said positive voltage, means connecting the difference output between said second and fourth amplifier to said second slice circuit means for slicing said negative voltage, an OR circuit, means connecting outputs of said first slice circuit and said second slice circuit to different input terminals of said OR circuit, a constant time hold circuit, said OR circuit passing said outputs of said first slice circuit and second slice circuit to said constant time hold circuit, said constant time hold circuit having a capacitor charged at a low impedance through said OR circuit and discharged at a comparatively high impedance, a pulse shaper, the output of said constant time hold circuit being shaped by said pulse shaper, an intensity modulation amplifier, means applying the output of said pulse shaper via said intensity modulation amplifier to an intensity modulating grid of said electromagnetic deflection type CRT.

Claims (4)

1. 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 VL proportional to the current change rate dI/dt in said deflection coil circuit, function generator means coupled to said VL generating means for generating a voltage Vd having a value which increases exponentially with respect to VL, 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.

1. 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 VL proportional to the current change rate dI/dt in said deflection coil circuit, function generator means coupled to said VL generating means for generating a voltage Vd having a value which increases exponentially with respect to VL, 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.

2. 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 VL proportional to a sweep current change rate dI/dt in a deflection coil of a CRT between terminals of said deflection coil, an operational amplifier, 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 R1 and R3, respectively, connected to terminals of said deflection coil and input terminals of said operational amplifier, a resister R2 connected between one input terminal of said operational amplifier and ground, a resistor R4 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'', R1, R2, R3 and R4: means for generating an unblanking pulse, means for applying the output of said operational amplifier to said means for generating an unblanking pulse, means receptive of the output of said means for generating an unblanking pulse applying it to the intensity modulation grid of said electromagnetic deflection type cathode ray tube.

3. A circuit for use in controlling the intensity of scanning in an electromagnetic deflection type cathode ray tube according to claim 2, 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.

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