DE2044909A1 - Display device and method for scanning it - Google Patents

Description

Patent attorneys DIpL-In ₉ . R.BEETZMI) DlpMng. K. LAMPRBCHT w | ngRBE

gBEETljr • ^{M0nch # a22} rS »., _TO dbrfctr. 10 2 04 A 9

81-16.O8ip 9/10/1970

HITACHI, LTD., 5-1,1-chome, Marunouchi Chiyoda-ku, Tokyo (Japan)

Display device and method for their

Scanning

The invention relates to a display device with a light transmitting arrangement and a method for scanning this arrangement

The known light emitting devices composed of a plurality of light emitting elements which are arranged in a matrix, use Liohtemissionsdioden (ab shortened LED) as Liohtsendeelenente · As · usual Vorfah ren for scanning such an arrangement for "ine indicator based on the principle that" Ine Liohteaissionsdlode, which is located at the bottom of a (horizontal) scanning cell and a (vertical) scanning column that are being scanned, emits Lioht * With such a scanning method, a Liohteaiseione-

81. (POS. 23052) -Hd-r (7)

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2QAA909

diode only briefly while the associated scanning line and scanning column are scanned. In a large array consisting of a large number of columns and rows, the lighting time of a light emitting diode is therefore only a small fraction of the total scanning time of the array, resulting in a display of insufficient luminance. In an arrangement of light-emitting diodes with 50 rows and 50 columns, for example, the lighting duration of a single diode is only I / 25OO of the display frame time since the light emitting diodes do not persist. To with a 50 χ 50 arrangement To achieve a luminance equal to that of a conventional cathode ray tube of 50 feet · Lambert (hereinafter abbreviated to f * L), the luminance would have to be of each light emitting diode 50 · 2500 = 125,000 f »L. Such a luminance can be achieved with the known Liohtemissiondioden are not produced, in particular not in low voltage, low current operation.

To overcome this problem, there is insufficient luminance because of the above-mentioned point scanning already a method for line or column scanning (i.e. for scanning one column or row at a time) in which the light information for an entire column or row is stored in a delay line in order to sequentially all the diodes arouse in the column or row at a time. However, this method requires rather large delay lines, which hinder the creation of a compact display device.

It is therefore the object of the invention to provide a Liohtsende-

109813/1191

B'S: ': -! »■■■■ ·' ■ -. ■

arrangement to indicate the same overall luminance θ as the above-mentioned line or column scanning method he » without using delay lines.

The object is achieved in that an element with switching behavior is connected in series with each of the row and column scanning lines of the arrangement.

An advantageous further development of the invention consists in that the light transmitting elements themselves exhibit switching behavior built-up combination of scanning pulses into the row or column scanning lines are fed

The invention is particularly when scanning the arrangement consisting of light emitting elements, if the light-emitting elements show switching behavior, achieved that the respective light-emitting elements during the largest Are excited part of the sampling period and therefore give an extremely bright display

The invention is explained in more detail with reference to the drawing. It shows

Flg. 1 shows the basic circuit diagram of a first exemplary embodiment of a light transmitting arrangement in FIG display device according to the invention;

Fig. 2 shows the course of pulses that are in the line

and column terminals of the arrangement of Fig. 1 are fed;

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Figure 3 is a modified _o during the pulse which is fed to the column terminals of the array;

FIG. K shows the basic circuit diagram of a second exemplary embodiment of the light transmitting arrangement according to the invention; FIG. and

Fig. 5 shows the course of pulses which are in the line

. are fed Spaltenanschliisse k and the arrangement of FIG.

Fig. 1 shows the circuit diagram of a first embodiment of the arrangement according to the invention. This arrangement has connections X ₁ X,. .., X, ·. ·, X _M of M line scan lines, terminals Y ₁ , Y _? , .. ·, Y, ··>, Y _n - of N column scan lines, a gate terminal G for the array, components SX ₁ , SX, ..., SX,. _0. , SX ,. or SY,

SY, ..., SY, ..., SY with switching behavior like thyristo- ^ c Ij. in

ren, which are connected to the row or column connections X - X and Y - Y ^ are connected.

2 shows the pulse waveform of row and column scanning pulses in Cartesian coordinates, the abscissa denoting time and the coordinate denoting the voltage. Pulses FY, FY, oo., FY, .β., FY _{n are} fed into connections Y ₁ - Y, while a pulse FX (M ^ m * 1) represents a pulse fed to connection X. The reference numbers 1, 2 and 3 denote voltage levels 0, -V 'and + ν _{γ of} the pulses FY ₁ - FY _n , similarly the reference numbers h _t 5 and 6 denote voltage levels 0, -V and -V for the pulse FX . It can therefore be seen

Lj Il m

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that a DC voltage -V _{T is} constantly at the terminals

L

X - X is present except for the time interval during which the voltage level from X to -V ₁ - (V ₁ - ^ V-) at the time-

m ti ti L

point t lowered and to -V. at time t again l L · m

will be produced. The voltage at each of the terminals Y. - Y "(N δ" η s 1) is normally zero except for Time interval in which the voltage at Y increases to -V to

Time t _i = t, + ^{K n} " ' ^y m" m-1 ' is decreased, n - 1 m - ι "'

is then increased to + V _y at time t · which is between

tt ^
t and t = t _Λ + n (m- m- 1) , and finally

η-1 η m— 1 ^il ".. '*

is brought back to zero at time t. The point in time t · can be arbitrarily between t _Λ and t, η η-1 η

It can be seen, however, that the time interval (t ¹ -t ₁ ) or (t -t ') may not be shorter than the time required to switch the switching element, which depends on the properties of the element concerned.

Deim illustrated embodiment of Fig. 1 and 2 is a thyristor for the switching elements SX ₁ S ^ and SY - SY-. used. Preferably, the thyristor operates with a relatively low voltage and a relatively low current. In other words, it is preferably made conductive by a gate current of mostly 100 / uA, the working voltage in the conductive state being approximately 1V. The gate connection G is connected to the control connection of all thyristors. The cathode allerZeilen thyristors and all the columns are thyristors (not shown) to the common line a Ans teuerschaltuntf each case via a diode and a capacitor gemiiß Fig. 1, respectively. The thyristors are controlled by a drive signal fed into the gate connection G. If the fed-in "in · Liohtemiaaionediode voltage V _Q and Haiteapannung the thyristor V _g loading

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carries, the bias voltage V _T = 2V "+ V_ is selected. Therefore, once the thyristors are switched to the conductive state, they remain in this state and the light emitting diodes at the intersections of the row and column scan lines connected to the conductive thyristors continue to emit light. Assuming that the m-th row and the n-th column are currently being scanned, a negative voltage becomes -V-. fed into the m-th line with the pulse profile FX of FIG. 2, while a signal consisting of a negative pulse with the height -V '(V "> - V ·" = V) and a subsequent positive pulse with the amplitude + V exists, is fed into the nth column,
as the pulse FY in FIG. 2 shows.

Let us now consider an electrical circuit

starting at port X and passing over to port Y.

'm η

the m-th row line and the n-th column line terminate, this circuit comprising two thyristors and a light-emitting diode. At a certain point in time t between t 'and t, a spanming V - V' is first applied to terminals X and Y. Then at a point in time between t and t 'a voltage V _x , + V _{v is}

n η rl ι

fed. When this voltage V + ν _{γ is} applied, the thyristors, which are blocked, remain blocked, if
a control pulse is not supplied to the terminal G in synchronism with the voltage V, + V _v. As a result, no current flows through the light emitting diode. A flow of strokes
by the light emitting diode, a drive pulse must be applied to the gate terminal G to an appropriate one
Time to be supplied. Because of the switching behavior of the thyristors, a thyristor remains once it has been controlled
leading, even after the point in time t. So that not just any-

109813/1191

a current flows through a light emitting diode, which with a row or column line is connected that is not

has been scanned. the levels V _T and V _{v are} so united I

shows that when a voltage V _Y + V is applied to the terminals X and Y, the thyristor is rendered non-conductive even if the drive pulse occurs at the gate terminal 6. Furthermore, the voltage levels V "and V" and the magnitude of the drive pulse are selected so that when the voltage V "+ V _{Y is applied} to the terminals X and Y, the thyristor is made conductive by the drive pulse fed to the gate terminal G. . To prevent incorrect operation, a larger difference between V „and V _{L is} recommended. On the other hand, the same difference should be as small as possible, since the light emission from a light emitting diode is not significantly affected by the application of the voltage V i.

Once activated, the light emitting diode does not return to the blocked state until the next time the associated column is scanned when a negative voltage -Vy ¹ at terminal Y occurs. Hence, if the bias voltage -V _T is applied to terminal X_, one

- Lj m

negative voltage V, - V _v * at terminals X and Y

^D LY mn

created. In this way, the thyristors SX and SY blocked, and the light-emitting diode at the intersection of the two associated lines is no longer connected Powered. From the preceding explanation it should be apparent that the duration of the light emission of the Light emitting diode corresponds to the time it takes to scan a line, i. H. t - t ...

m m - ι

In the preceding explanation, the simple

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For the sake of sake, it has been assumed that a thyristor is used as the switching element. It is evident, however, that other components with a similar switching behavior can also be provided. Furthermore, the course of the line scan pulses was shown to be rectangular. However, this pulse course is not mandatory. An example of a modified pulse course can be seen in FIG. 3, where 7 an output pulse from a shift register, 8 the pulse obtained by differentiating the pulse 7, L · which can be used as a sampling pulse, and 9 »10 or« 11 the voltage level Designate O, -V 'and + V _v , respectively.

In a tried and tested embodiment of the display device according to the invention, the light-emitting diodes were GaAS / -P _n ι diodes, which were arranged in a 6 mm spacing and matrix arrangement of 7 rows and 5 columns, while the switching elements were thyristors of the 2SF 656 type were formed. 1S79H type diodes and 10 / uF capacitors were provided for the gate circuit of FIG. This arrangement was scanned by the method described above, using the following operating values:
»

-V = - ^ ^V "* '" - * n-1 = ²⁰ / ^US;

+ V _Y = 5 V, t _n - f _n - 5 / us;

-V _L = - 1/1 V, -V _H = -20 V, t _m - t _m-1 = 140 / us.

The column strobe was in the column terminals fed in via a resistance of 2 kO »When the light-emitting diodes were conducting, they flowed through them a current of 10 mA. A luminance of 9 f * L was achieved under these conditions. However, if this arrangement

10981 3/1191

was scanned by an ordinary method only a luminance of 2 f »L,

Fig. K shows another embodiment of the display device according to the invention. In this embodiment, light-emitting diodes with switching characteristics are used as the light-emitting elements of the arrangement. In Fig. K , terminals having similar functions are denoted by the same reference numerals as in Fig. 1. The pulse waveform of the sampling signals may be substantially the same as that shown in Fig. 2, although the peak values or levels of these signals are different from those in the previous embodiment can be different, which depends on the properties of the components · Furthermore, the mode of operation is essentially the same as that described for the first embodiment example »

The ligth-end assembly of Fig. K can be operated as a display device which has a very high luminance when scanned by the following method. Figure 5 shows the pulse waveforms of the row and column scan signals used in this method. Sampling pulses GY., ···, ^GY _n »···» G ^Y _{N are} fed into the column connections Y ₁ , Y-, ···, Y _{,. ·., Y n} , while GX (M £ ra * i ) indicates the course of the line scan signal which is fed to the terminal X. Reference numerals 11 and 12 denote voltage levels zero and + ν _γ for the pulses GY - GY _n and reference numerals 13, 14, 15 and λβ for the pulse GX with the level zero, -V ,, -V "and an arbitrary level, which is not lower than V _y 1st. From Fig. 5 it can be seen that normally a voltage of constant level -V ^

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is supplied to the row connections, unless the voltage is increased to a level which is not lower than ν _γ , namely at time t ¹ .., which is earlier by at least the time required to switch the device than the time t occurs when the scanning for the m-th line begins, so that all conductive elements in the m-th line are blocked, after which the voltage to the level -V (V "^ k V _T ) at the time-

^ point t lowered and to the normal level -V _T for m - ι Lj

Time t is reset. The potential of the connections Y - Y _n is normally zero. However, the potential of an optional connection Y (N = η = 1)

to the level + ν _γ at the point in time

*. *. (ni) (t -t J t, = t. + ^v ' ^v m m-1 '

n- 1 m- 1 rr-

increased and then to zero at the time

. . n (t -t.)
t = t _Λ + ^x m m-1 '
η m-1 yy——

brought back. As in the operation of the first embodiment a drive pulse is fed to the gate terminal G in synchronism with the column sampling pulse which the Column is supplied to which the element to be excited belongs.

It should now column to be considered a light emitting element at the intersection of the m-th line and the th η-, wherein a voltage, the nioht less than + _{γ ν} is, first at the terminal X during t ^1., And t, is applied,

m m - 1 m - ι

in order to lock all elements in the m-part line. Then the potential of connection X is set to -V ₁₁

m H

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low while the columns are scanned with a pulse whose height is V _v . So there is a voltage V "+ \ in the element during t. to t turned-Ii χ η— ι η

feeds »If the control pulse is not fed to the gate connection G at this point in time, it remains Element locked so that it does not emit light · On the other hand, when the drive pulse is supplied, the Made element conductive and maintain its light emission, until the next time the m-th line is scanned. It can be seen that the duration of light emission is slightly different for each column as the ratio of the duration for the first column to that for the last or Nth column M: M-1 is. However, if M is large enough, the constancy of the luminance on the entire display panel is sufficient for practical purposes. If required, it is possible to visually compensate for the lack of constancy in luminance by scanning the columns in a Sequence is undertaken which deviates from the geometric sequence of the columns.

In a practically tested embodiment of the display device according to FIGS. K and 5, PNPN light-emitting elements were used in a 6 mm spaced matrix arrangement with 7 rows and 5 columns. This arrangement was scanned using the method described in connection with FIG main operating values were as follows

+ V _Y = ♦ 5 V, t _n - ^ ₁ = 5 / us,

-V. _L = -14 V, -V _H = -20 V, t _m - t ^, = IUO / us;

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furthermore, the height of the positive pulse before the negative pulse in line scanning was + 5 V (+ IQ V related to -V) and the width of the last such pulse 20 yus. A current flowed through a conductive element 10 raA, under these conditions a luminance of 50 f »L was achieved»

It should be noted that the pulse waveform of the sampling pulses of FIGS. 2 and 5 is shown in a simplified manner

fc has been made to facilitate understanding of the invention, d. H. impulses with a different course can also be used. For example is in the previous one Description has been assumed that the width of the column scan timpulse l / N of the width of the line scan pulse However, there is no particular relationship between the width of the column strobe pulses and the duration the light emission of the element, so that the width of the column scanning pulses can be chosen optionally so long as it only stays longer than the time required to switch the elements and not otherwise interferes with temporal relationships. Furthermore, it is not necessary that the pulse to block a conductive EIe-

"Ments (the negative pulse of FY -. FY of Flg 2 or the positive pulses GX in Fig. 5) to the pulse for rendering conductive of the element (the positive pulse of FY FY in Figure ₀ 2 or the negative pulse of GX in Figure 5) continues, but it is important that the former precede the latter, and it should be understood that the rows and columns in the foregoing description may be interchanged.

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Claims (3)

■?! '■' ~ ' ^Ί F'Wfref iff? ¹ 'S -'-: ■!'; ■ -> -: ', -ί ρ «· ■. - 13 - Claims ( 1 c ^ display device with a light-emitting arrangement which has a number of light-emitting diodes arranged in a matrix arrangement, one terminal of a number of terminals being assigned to each row and column of the matrix arrangement, characterized in that in each case one of a number of components (SX, ..., SX ..) is assigned with switching behavior of each row of the matrix arrangement, of which the anode is connected to the cathode of each light-emitting diode of the row in question and the cathode to the row connection (X ₁ , ···, Xw) that each one of a number of components (SY, ··· »SY“) with switching behavior is assigned to each column of the arrangement, of which the cathode with the anode of each light-emitting diode of the relevant column and the anode with the column connection (Y ₁ I ···, ^Y _N ) is connected, and da'.i a gate connection (G) is connected to the control connections of all components with switching behavior (Fig. 1). 2. Display device with a light emitting arrangement which has a number of light emitting elements which are arranged in a matrix arrangement, and with a number of connections, each of which is assigned to each row and column of the matrix arrangement, characterized in that the Liohtsendeelemente show switching behavior, that the row terminals (X ~, ···, X ") are connected to the cathode of each light- _{emitting element of the relevant row, that the column terminals (Y 1} , ···" Y ") are connected to the anode of each wire end element of the relevant column, and that a gate connection (G) with 10 9 813/1191 is connected to the control terminal of each light emitting element (Fig "4). 3. A method for scanning the display device according to claim 1 or 2, characterized in that the column connections (Y ₁ I. «· Ι ^Y _N ) with a column scanning pulse (FY,. .., ^ Y _n ) are scanned from a first, negative section (2) and a second, positive section (3), while the row connections (X, · .., X »,) are normally subjected to a negative voltage (5) which is smaller than the negative part ( 2) of the column scanning pulse, but one of the row connections that is being scanned is subjected to a negative voltage (6) which is more negative than the negative part (2) of the column scanning pulse when a light-emitting element connected to this row connection (X) is closed is energized, and that a drive pulse is fed into the gate terminal (G) in synchronism with the feeding of a column scanning pulse into the column terminal connected to the light emitting element to be excited, so that a light emitting element which le it has been made is blocked again before the column connection to which this conductive light seride element is connected is scanned the next time (Fig. I, 2; k), h ₀ Method for scanning the display device according to claim 2, characterized in that the potential of the Spnl teianschliisse (^ i »···» ^ m) is normally kept at zero (ii), but that a positive pulse (GY, .. ., GY \ is fed into one of the column connections during the scanning period for the column if a light emitting device connected to the column connection 1098 13/1191 element is to be excited that the row connections (X, • .., Xj.) are normally subjected to such a constant negative voltage (i * 0 that a controlled light-emitting element is kept in the conductive state that the row connections with a pulse (GX ) which has a positive portion (16) not lower than the opaltite strobe (12) and a subsequent negative portion (15) that a drive pulse is fed to the gate terminal (G) in synchronism with a column strobe which f is fed to that column connection which is connected to the light element to be excited, so that a light-emitting element which has been made conductive is blocked again before the column connection connected to this conductive light-emitting element is scanned the next time (Fig. k, 5) · 109813/1 191 / lt. Blank page