United States Patent [191
`Kaelin et al.
`
`3,740,570
`[111
`[45] June 19, 1973
`
`[54]‘ DRIVING CIRCUITS FOR LIGHT EMITTING
`DIODES
`[75] Inventors: George R. Kaelin, Woodland Hills;
`James A. Pelligrino, Thousand Oaks,
`both of Calif.
`[73] Assignee: Litton Systems, Inc., Beverly Hills,
`Calif.
`Sept. 27, 1971
`[22] Filed:
`[21] Appl. No.: 184,076
`
`[52] U.S. C1. ...... .. 307/40, 178/7.3 D, 315/169 TV,
`340/166 EL, 340/324 R
`[51] Int. Cl. ......................................... .. 11051) 33/00
`[58] Field of Search ............. .. 307/40; 315/169 TV;
`' 340/324 R, 166 EL, 334, 343; 178/5.4 EL, 7.3
`D; 317/235
`
`[56]
`
`3,021,387
`3,517,258
`
`References Cited
`UNITED STATES PATENTS
`2/1962 Rajchman ................ .. l78/5.4 EL X
`6/1970 Lynch ......................... .. 315/169 TV
`
`3,603,833
`
`9/1971
`
`Logan ........................... .. 317/235 X
`
`3,388,255
`
`6/1968 May . . . . . . . . . . . .
`
`. . . . . . . . .. 178/7.3 D
`
`3,511,925
`3,595,991
`3,611,069
`
`.. 178/73 D X
`5/1970 Lee et a1.....
`178/5.4 EL
`7/1971
`Diller .......... ..
`10/1971
`Galginaiths ....................... .. 317/235
`
`Primary Examiner-Robert K. Schaefer
`Assistant Examiner-William J. Smith
`Attorney-Robert M. Angus, Alan C. Rose and
`Alfred B. Levine
`
`ABSTRACT
`[57]
`LEDs are arranged in a matrix and driven by a pair of
`registers. A column register sequentially enables the
`columns of LEDs and a row register selectively oper
`ates the LEDs of each column in accordance with a
`predetermined binary code. A color control and a
`brightness control circuit may be included in connec
`tion with the row register to selectively control driving
`currents to the LEDs to control color hue, and to selec
`tively control the duration of “on” time to control ap
`parent brightness.
`17 Claims, 5 Drawing Figures
`
`34)
`E/Q/GHT/Vf??
`CONTIQOL
`
`F/Q‘OM
`2 m
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`
`r
`38
`
`39
`
`To 450 ROW
`
`YELLOW
`REF.
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`TCL 1030, Page 1
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`

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`Patented June 19, 1973
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`3,740,570
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`,7
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`.2 Sheets-Sheet 1
`
`
`
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`
`INVENTORSl
`GEORGE E. KAEL/N,
`JAMES A. PELLEGE/NO
`
`“Sr“
`
`’477'0R EY.
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`TCL 1030, Page 2
`TCL 1030,'Page 2
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`Patented June 19, 1973
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`3,740,570
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`2 Sheets-Sheet 2
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`32]
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`33
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`TCL 1030, Page 3
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`3,740,570
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`15
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`1
`DRIVING CIRCUITS FOR LIGHT EMITTING
`DIODES
`This invention relates to driving circuits for light
`emitting diodes, and particularly to circuits for driving
`light emitting diodes to achieve color display.
`Light emitting diodes (LEDs) are useful for alpha
`numeric display purposes. LED matrices, when prop
`erly driven, can provide alpha-numeric read out of in
`formation from a computer. However, in prior LED
`matrices, the individual diodes were separately oper
`ated, so that driving circuits required for operating
`prior LED displays required numerous connections to
`the display. The number of connections to prior LED
`display matrices rendered such matrices cumbersome
`in use and often expensive to manufacture.
`It is an object of the present invention to provide
`driving circuits for LED display matrices whereby the
`LEDs may be selectively operated.
`It is another object of the present invention to pro
`vide a LED driving and memory circuit which may be
`integrated with a LED matrix to form LED display ap
`paratusrequiring fewer interconnections than hereto
`fore achieved.
`‘
`'
`Certain LEDs exhibit different colors when subjected
`to driving currents of various amplitudes. Accordingly,
`it is yet another object of the present invention to pro
`vide a driving circuit for a LED matrix for selectively
`varying the driving currents to the individual LEDs of
`the matrix to achieve a selectable color display.
`Another object of the present invention is to provide
`intensity control apparatus in multicolor LED display
`apparatus.
`Another object of the present invention is to provide
`a LED driving circuit for selectively varying'the pulse
`widths of driving current pulses to achieve selective in
`tensity control of- the LEDs.
`‘ In accordance with the present invention, a plurality
`of LEDs are disposed in a two-dimensional matrix. The
`LEDs are arranged in rows and columns. A ?rst shift
`7 register is provided for driving the LEDs along the rows
`and a second shift register is provided for driving the
`LEDs along the columns. Information is stored in the
`shift registers to effectuate selective driving of selected
`ones of the LEDs.
`'
`In accordance with one feature of the present inven
`tion, the driving circuit includes means for selectively
`applying driving currents of various amplitudes to the
`LEDs so that the LEDs display selected colors.
`In accordance with another feature of the present in
`vention, means is provided for varying the pulse widths
`of the driving current pulses to selectively vary the in
`tensity of the display.
`7
`The above and other features of this invention will be
`more fully understood from the following detailed de
`scription and the accompanying drawings, in which:
`FIG. 1 is a schematic block diagram of a LED display
`matrix having a driving circuit in accordance with the
`presently preferred embodiment .of the present inven
`
`2
`FIG. 5 is a block logic diagram of a color driving cir
`cuit for controlling the intensity and the color of dis
`play of light emitting diodes in accordance with an
`other embodiment of the invention.
`Referring to FIG. 1 there is illustrated a matrix 10
`having m number of leads 11, 11a, etc. arranged in
`rows and n number of leads 12, 12a, etc. arranged in
`columns. Leads 11 and 12 are electrically isolated, and
`are interconnected by a matrix of m n number of light
`emitting diodes 13. For example, the anode of each
`diode 13 may be connected to a respective lead 11
`while the cathode of the diode may be connected to a
`respective lead 12. Leads 11, 11a, etc. are connected
`through resistors 14, 140, etc. and integrated circuits
`15, 15a, etc. to individual outputs of m register 16. The
`input for register 16 is connected to the output of shift
`register 17. Leads 12, 12a, etc. are connected through
`transistors 18, 18a, etc. to ground, the base of each
`transistor 18 being connected to a separate output of
`n register 19.
`Register 19 is a shift register capable of sequencing
`enable signals to the various outputs of the register.
`Shift register 19 has a ?rst input 21 for resetting the
`register and to condition operation of the first transis
`tor 18. A second input is connected to slave clock 23
`to sequence an enable signal to the outputs of register
`19 to sequentially operate transistors 18, 18a, etc. Reg
`ister 17 has an input 20 for supplying data to register
`17. The input data may be supplied by means (not
`shown) which develops the input signals in accordance
`with data to be displayed. The input data to register 17
`includes at least one bit for each LED device in matrix
`10. As will be more fully understood hereinafter, the
`input data may include more than one bit per LED de
`vice to achieve color and intensity control.
`Master clock 22 is connected to one input of storage
`register 17 and shift register 16, and .is connected to an
`input of slave clock 23. The output of clock 23 is con
`nected to an input of shift register 19. As illustrated in
`FIG. 1, storage register 17 includes alfeed-back path 24
`connecting the output of the storage register to its in
`put.
`With reference to FIG. 2, the operation of the driving
`circuit illustrated in FIG. 1 may be explained. Light
`emitting diodes 13 are connected between each lead 12
`and each lead 11 so that connection is made from the
`m e register 16 through the light emitting diodes l3 and
`transistors 18 to ground, input data is supplied to stor
`age register 17. The input data to register 17 comprises
`at least m n number of bits of information, where m is
`equal to the capacity of register 16 and n is equal to the
`capacity of register 19. As will be more fully under
`stood hereinafter, the input data may include some
`multiple of m n bits for color and intensity control.
`With an m by n matrix 10, the input data to storage reg
`ister 17 corresponds in length to some multiple of the
`number of diodes in matrix 10.
`'
`Master clock 22 is operated at a frequency equal to
`x m n m where m is the display cycle refresh frequency
`of the display, and where x is the number of bits associ
`ated with the color and intensity control circuits, if any.
`Master clock 22 conditions storage register 17 to store
`x m n bits of input data, and clocks register 16 to accept
`x m bits from register 17 during each cycle 0). Master
`clock 22 also drives slave clock 23 to supply it pulses
`to register 19 to step the output of register 19. The bi
`nary value of each bit of information stored in m regis
`
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`FIG. 2 is a diagrammatic representation of wave
`forms associated with the driving circuit illustrated in
`FIG. 1;
`FIG. 3 is a diagram illustrating the color display char
`acteristics of a light emitting diode;_
`FIG. 4 is a schematic block diagram of a logic circuit
`for color control of light emitting diodes in accordance
`with one embodiment of the invention; and
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`ter 16 operates through integrated circuit 15 to control
`the current on each of leads 11. The presence of the n
`pulse to the input of n register 19 conditions the first
`transistor 18 to conduct. Hence, current flows through
`integrated circuits 15, through the light emitting di
`odes, and transistor 18 in accordance with the binary
`value of the signals stored in register 16. For example,
`if eight rows 11 are connected to register 16, m equals
`8, and the x m code will consist ofx 8 bits. If no color
`or intensity circuits are associated with integrated cir
`cuits 15 (so x=l ), each “l” bit from register 16 will
`supply sufficient current to condition the diodes con
`nected to the respective row leads to conduct, whereas
`those diodes receiving a “0” bit will not be conditioned
`to conduction. Energization of a selected transistor 18
`for each column will complete the conduction path for
`the LEDs so that those LEDs associated with the l’s
`from register 16 and associated with the particular col
`umn 12 will be energized.
`Assuming, for example, that the display is to be in
`single color and single intensity (Fl) during the first
`n pulse 25, m pulses 26 are stored into register 16.
`Pulse 25 also conditions register 19 to provide an out
`put to transistor switch 18 to complete a path for all di
`odes in the ?rst column. The period of conduction for
`transistor 18 is shown at 27 in FIG. 2. The LEDs remain
`on during the remainder of pulse 27, at which time
`clock 22 conditions a new set of m pulses 29 to be
`stored in register 16. At the same time, clock 22 drives
`clock 23 to condition shift register 29 to its second out
`put to transistor switch 18a. Transistor 18a conducts
`for the period illustrated at 30 in FIG. 2.
`If during the-?rst n pulse, the m pulse‘ pattern is
`110101 10 and the integrated circuits are condition to
`respond to only the l’s of the code, it is evident that the
`first, second, fourth, sixth and seventh LEDs of the first
`column will be energized. If during the second n pulse,
`the m pulse pattern is 00l 1 1010, it is evident that the
`third, fourth, ?fth and seventh LEDs of the second col
`umn will be energized. The pattern continues through
`the entire cycle of n register 19. By establishing the
`cycle frequency w of n register 19 sufficiently high, the
`selected LEDs of the matrix will appear, to the human
`eye, to be conducting at the same time. The m n pulses
`are recycled through register 17 through loop 24 so
`that the display will continue for any desirable period
`of time.
`One feature of the present invention resides in the
`utilization of the color emitting capabilities of certain
`light emitting diodes. For example, gallium phosphide
`light emitting .diodes available from Bowmar Canada,
`Ltd., when subjected to a low current emit a predomi
`nantly red light. However, when subjected to a rela
`tively high current, such diodes emit a predominantly
`green light. The brightness of the red and green hues is
`illustrated in FIG. 3 as a function of current. At low
`currents, the red hue, illustrated by waveform 32 is pre
`dominate over the green hue, illustrated by waveform
`31, whereas at high current the green hue predomi
`nates. At cross-over point 33, the hues are about equal
`and will blend to appear as yellow.
`FIGS. 4 and 5 relate to driving circuits to take advan
`tage of the color phenomenon for selective color dis
`play from LED matrices. The circuits illustrated in
`FIGS. 4 and 5 may be used for integrated circuits 15 in
`FIG. 1. In FIG. 4, brightness control circuit 34 has out
`put leads 35, 36 and 37. As will be fully understood
`
`4 .
`hereinafter, brightness control 34 provides pulses of
`different pulse widths on the output leads 35, 36 and
`37. Input leads 38 and 39 are connected to a shift regis
`ter having a length equal to 2 m, since F2 to provide
`for conditions for each LED, three colors and off. For
`example, the shift register to which leads 38 and 39 are
`connected is similar to register 16 illustrated in FIG. 1
`but so arranged that two bits of information will oper
`ate on the circuit illustrated in FIG. 4. Lead 38 provides
`an input to bistable multivibrator 40, and lead 39 pro
`vides an input to multivibrator 41. Multivibrators 40
`and 41 each have two outputs, output 42 of multivibra
`‘tor 40 being connected to an input of AND gates 43
`and 44, output 45 of multivibrator 40 being connected
`to one input of AND gate 46, output 47 of multivibra
`tor 41 being connected to inputs of AND gates 43 and
`46, and output 48 of multivibrator 41 being connected
`to the second input of AND gate 44. AND gate 49 has
`inputs connected to the output lead 35 from brightness
`control circuit 34 and to the output from AND gate 43,
`AND gate 50 has inputs connected to the output 36 of
`brightness control circuit 34 and to the output of AND
`gate 46, and AND gate 51 has inputs connected to out
`put lead 37 from brightness control circuit 34 and to
`the output from AND gate 44. Each of AND gates 49,
`50 and 51 are connected to the base of respective tran
`sistors 52, 53 and 54. The emitters of transistors 52,53
`and 54 are connected to respective sources (not
`shown) of constant voltage through resistors, and the
`collectors of transistors 52, 53 and 54 are connected
`together to lead 11 of the particular LED row. The
`driving currents established by the voltage sources and
`series resistors are different for each transistor 52, 53
`and 54. For example, the source connected to the emit
`ter of transistor 52 may produce a relatively high cur
`rent for green displays, the source connected to emitter
`of transistor 53 may produce a relatively low current
`for red displays, and the source connected to the emit
`ter of transistor 54 may produce an intermediate cur
`rent for yellow displays.
`The brightness of a particular LED is determined by
`the current applied to that diode, which also affects the
`color hue. However, the “apparent” brightness of such
`diodes, as perceived by the human eye, is determined
`by the length of time that the diode is emitting light, as
`well as actual brightness. Hence, if it is desirable to pro~
`vide an apparent bright display of red colors, brightness
`control circuit 34 provides pulses of longer duration on
`output lead 36 than the pulses on the leads 35 and 37.
`On the other hand, if it is desired that all colors have
`substantially the same apparent brightness, the length
`of pulses applied to each lead 35-37 is inversely pro
`portioned to the pulse amplitude so that the average
`current to each lead is substantially the same. However,
`the pulse lengths may be adjusted somewhat to com‘
`pensate for the differing efficiency of the human eye
`for different colors.
`In operation of the color driving circuit illustrated in
`FIG. 4, the input signals representative of 1's and O’s
`are applied to input leads 38 and 39. Multivibrators 40
`and 41 provide output signals at one or the other of
`their outputs depending on the binary value of the
`input signals. For example, if the input signal to lead 38
`is a “ l ," multivibrator 40 will provide an output at lead
`42, where as if the input lead 38 is a “0,” multivibrator
`40 will provide an output at lead 45. Likewise, multivi
`brator 41 will provide an output at lead 47 if its input
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`is a “l,” and will provide an output at lead 48 if its
`input is a “0.” AND gates 43, 44 and 46 are arranged
`so that a “ll” condition will operate through 'AND
`gate 49 to operate transistor 52, whereas a “()1 ” code
`will operate transistor 53 and a “ 10” code will operate
`transistor 54. A “00” code will not operate any of the
`transistors. Selective operation of transistors 52, 53 and
`54 provides selective current control to the LED row.
`If a “l l ” code is applied to leads 38 and 39, gate 49 is
`operated for a period of time determined by the pulse
`length on lead 35 to operate transistor 52 to apply a rel
`atively high current from the current source to LED
`row 1 1. If a “01 ” code is applied to the input, transistor
`53 is operated to drive LED row 11 with a relatively
`low current for a period of time determined by the
`pulse length on lead 36. An intermediate current is ap
`plied to row 11 upon operation of AND gate 51 and
`transistor 54 for a period of time dependant on the
`pulse length on lead 37.
`FIG. 5 illustrates another color driving circuit which
`provides both a color decoding system as well as auto
`matic control of the brightness of the particular LED
`being operated. In FIG. 5, information from the storage
`register, such as storage register 17 in FIG. 1 is for
`warded via channel 60 to shift register 61. The code for
`each LED row includes a ?ve digit binary code, the ?rst
`three bits providing the brightness code, and the last
`two bits providing the color code. The brightness code
`is capable of selecting seven levels of brightness, as well
`as an off condition. Color decoder 62 is connected to
`shift register 61 to receive the two bits representative
`of the color code. Color decoder 62, which may be sim
`ilar to that illustrated in FIG. 4, decodes the two bit
`color code and provides an output to a selected one of
`AND gates 63, 64 and 65. The output of AND gates 63,
`64‘and 65 are connected to lead 11 of the LED row '
`being operated.
`Decoder 66 is connected to the output of register 67
`which in turn is connected to receive the three bit
`brightness code from shift register 61. Register 67 op
`erates on the brightness, or gray scale code, by stepping
`the code until a “l l l ” code is reached. The stepping
`occurs at rate dependent upon the rate of clock pulses
`on lead 68. Decoder 66 will provide an output pulse for
`each pulse necessary to step the gray scale code to a
`“1 l l ” condition. Decoder 66 is connected to AND
`gate 69 which, in turn, is connected to monostable mul
`' tivibrator 70. The output of monostable multivibrator
`is connected to a second input of each of AND gates
`63, 64 and 65.
`In operation of the apparatus illustrated in FIG. 5, a
`five bit code is applied to shift register 61 in accor
`dance with a signal from the data storage over lead 60.
`, The input signal is clocked into register 61 via lead 71.
`Two of the bits of the code are decoded by color de
`coder 62 to selectively enable one of AND gates 63, 64
`and 65. AND gates 63, 64 and 65 include current driv
`ing means (not shown in FIG. 5) for deriving separate
`driving currents for each AND gate. For example,
`AND gates 63-65 may include transistor switch means
`and separate current sources as described and illus
`trated in connection with FIG. 4. In the even that gate
`63is operated, a relatively high current is supplied to
`the LED row so that the LEDs will emit a green color.
`If AND gate 64 is operated, a relatively low current is
`provided to lead 11 so that the LEDs will provide a red
`display. If AND gate 65 is operated, an intermediate
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`current is provided to lead 11 to provide a yellow dis
`play. The duration of operation of a particular AND
`gate 63, 64 and 65 is determined by register 67, de
`coder 66 and monostable multivibrator 70.‘
`Decoder 66 decodes the three bit gray scale code by
`stepping the code to a “111" condition and providing
`output pulses for each step. For example, if the three
`bit gray scale code is “1 10,” clock 68 operates on regis
`ter 67 only once to step the code to “ll 1." Hence, a
`single pulse is passed by decoder 66 to AND gate 69
`and thence to monostable multivibrator 70. Multivibra
`tor 70 is operated once to provide a single pulse, whose
`duration is determined by the time constant of the mul
`tivibrator, to the operated AND gate 6345. Hence, the
`selected AND gate 63-65 (selected by the color code)
`is operated during the single pulse to provide a current
`output of selected magnitude and selectively short du
`ration. However, if the gray scale code is “000,” clock
`68 must step through seven cycles to shift register 67
`to its “1 l 1” position. The seven pulses are passed
`‘ through decoder 66 and AND gate 69 to monostable
`multivibrator 70 to operate the monostable multivibra
`tor 70 seven times to provide seven successive pulses
`to the operated AND gate. The LEDs operated on the
`LED row 11 are operated for seven successive pulses
`to provide the appearance of a relatively long duration
`of “on” condition. Hence, the display is perceived by
`a human as being brighter utilizing a greater number of
`successive pulses in the decoded gray scale code as op
`posed to less numerous pulses. (A “l l l ” input code
`will not be stepped, so multivibrator 70 will not be op
`erated. Hence, a “1 1 l ” input code represents an “of ”
`condition for the particular LED row.)
`The apparatus illustrated in FIG. 5 is particularly ad
`vantageous where it is desirable to selectively control
`the apparent brightness of a'display. For example, in
`the event that it is desirable to provide a warning indi~
`cation, it may be desirable to display such warning in
`a red color and with a relatively intense brightness.
`With the apparatus illustrated in FIG. 5, it is possible
`to operate the LEDs from a relatively low intensity
`green display to a relatively high intensity red display
`merely by altering the code from the computer storage
`memory.
`The present invention thus provides apparatus for
`driving LEDs for selective brightness as well as selec
`tive color. The apparatus is effective in operation and
`provides a wide variety of uses.
`This invention is not to be limited by the embodi
`ments shown in the drawings and described in the de
`scription, which are given by way of example and not
`of limitation, but only in accordance with the scope of
`the appended claims.
`What is claimed is:
`1. Apparatus for driving selected ones of m times n
`light emitting diodes where m and n are whole num
`bers, comprising: first register means having at least m
`outputs and second register means having n outputs,
`each output of said first register means being con
`nected to one side of one diode in each of n mutually
`exclusive groups of diodes and each output of said sec
`ond register means being connected to the other side
`of one diode in each of m mutually exclusive groups of
`diodes, each diode being in one of said groups of m di
`odes and in one of said groups of n diodes; storage
`means connected to said first register means for storing
`at least m times n bits representative of information to
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`be displayed, said storage means having a feedback
`path for recycling m times n bits, and clock means con
`nected to said storage means and to said ?rst register
`means for initiating said storage means to transfer a bi
`nary code containing at least m bits to said ?rst register
`means for conditioning selected groups of said m
`groups of diodes for conduction, said clock means fur
`ther conditioning said second register means for condi
`tioning a group of said n groups of diodes for conduc
`tion, diodes existing in both the selected groups of m
`diodes and the selected group of n diodes being oper
`ated for a predetermined period of time, said clock
`means sequentially conditioning said storage means to
`transfer successive said binary codes to said ?rst regis
`ter means and shifting said second register means to op
`erate diodes existing in both the selected groups of m
`groups of diodes and the selected group of n groups of
`diodes until selected diodes in each group of said n
`groups of diodes are operated, said storage recycling m
`times n bits to repeat the pattern of operating said di
`20
`odes.
`,
`2. Apparatus according to claim 1 wherein said first
`register means includes m current source means con
`nected to respective outputs of said first register means,
`each of said current source means being conditioned by
`said ?rst register means to provide a predetermined
`current to the diodes of a respective group of n diodes.
`3. Apparatus according to claim 2 wherein said sec
`ond register means includes n switch means connected
`to respective outputs of said second register means,
`each of said switch means providing a current path be
`' tween the diodes of a respective group of m diodes and
`said current source means.
`4. Apparatus according to claim 2 wherein said di
`odes are characterized by emitting predominantly dif
`ferent color hues when driven by respectively different
`currents, and wherein each of said current source
`means includes a plurality of current sources each
`adapted to supply a current of mutually different pre
`determined magnitudes, and means responsive to the
`binary code in said ?rst register means for selectively
`connecting on of said current sources to the respective
`group of n diodes.
`5. Apparatus according to claim 4 wherein the binary
`code transferred to said first register means contains at
`least 2 in bits, and each of said current source means
`includes decoder means for decoding 2 bits of said bi
`nary code in said ?rst register means to selectively op
`erate said current sources.
`6. Apparatus according to claim 4 further including
`brightness control means for operating said current
`sources for a predetermined period of time.
`7. Apparatus according to claim 6 wherein said
`brightness control means comprises means responsive
`to a predetermined code in said ?rst register means for
`controlling the duration of time that current from the
`selected current source is applied to the respective
`group of n diodes.
`8. Apparatus according to claim 6 wherein said bi
`nary code transferred to said first register means con
`tains at least ?ve m bits, said current source means in
`cluding first decoder means for decoding two of said
`bits to selectively operate said current sources and said
`
`8
`brightness control means including second decoder
`means for decoding three of said bits for selectively
`controlling the duration of operation of said selected
`diodes.
`9. A driving circuit for energizing light emitting di
`odes of the class which emit predominantly different
`color hues when driven by respectively different cur
`rents, said circuit including current source means
`adapted to selectively provide one of a plurality of dif
`ferent predetermined current magnitudes; output
`means adapted to be connected to said diodes: and de
`coder means responsive to a binary input code for se
`lectively connecting said current source means to said
`output means.
`10. Apparatus according to claim 9 wherein said cur
`rent source means comprises at least three current
`sources each capable of providing a different current
`magnitude and said decoder means is adapted to re
`ceive a two~bit binary signal to decode said signal to se
`lectively connect one of said current sources to said
`output means.
`.
`11. Apparatus according 'to claim 9 further including
`control means for operating said decoder means for a
`predetermined period of time.
`12. Apparatus according to claim 11 wherein said
`control means comprises second decoder means re
`sponsive to a binary input code for controlling the du
`ration of time that current from said current source
`means is applied to said output.
`13. Apparatus according to claim 11 wherein said bi
`nary input code includes at least ?ve bits, said ?rst
`named decoder means being responsive to at least two
`of said bits to selectively connect said current magni
`tudes to said output means, and said control means in
`cludes second decoder means responsive to at least
`three of said bits for selectively controlling the duration
`of operation of said ?rst-named decoder means.
`14. Apparatus according to claim 13 wherein said
`current source means comprises at least three current
`sources each capable of providing a mutually exclusive
`current magnitude and said decoder means is adapted
`to receive a two-bit binary signal to decode said signal
`to selectively connect one of said current sources to
`said output means.
`15. Apparatus according to claim 1 wherein said ?rst
`register means produces x m output bits, in number of
`circuit means each responsive to mutually exclusive x
`number of bits for producing driving currents each hav
`ing a current amplitude dependent upon the bit pattern
`of said respective x number of bits, and means connect
`ing each of said circuit means to respective ones of said
`groups of n diodes.
`'
`16. Apparatus according to claim 15 wherein each of
`said circuit means is responsive to a respective x
`number of bits to produce a driving pulse having a cur
`rent amplitude and a time duration dependent upon the
`bit pattern of said respective x number of bits.
`17. Apparatus according to claim 1 wherein said sec
`ond register means conditions said groups of m diodes
`in sequence, whereby diodes in a single group of m
`diodes as selected by said second register means are op
`erated by said first register means.
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`TCL 1030, Page 7
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