EP0215262A1 - Method and circuit device periodically driving multiple radiation-emitting elements - Google Patents

Abstract

The invention relates to a method for the periodic activation of a plurality of radiation-emitting elements. The invention consists in that differences in the radiation power of the individual elements, which are caused by variations in the efficiency of the elements or by different operating conditions, are compensated for in that the radiation-emitting elements are each operated with an individual pulse length which determines the total radiation duration. In this way, the radiated energy of all controlled elements is essentially the same size.

Description

Methods for the periodic activation of several radiation-emitting elements are becoming increasingly important, for example, in information technology. For example, lines of luminescent diodes strung together are used for the exposure of photoconductive drums in data printing systems and are controlled via integrated circuits in accordance with the image pattern to be displayed. For example, the company TELEFUNKEN electronic GmbH has developed a light-emitting diode module with the designation TPHM 8080, the width of which corresponds to a DIN A4 page and which consists of 2560 gallium-arsenide-phosphide-luminescent diodes and 20 integrated silicon circuits for controlling the light-emitting diodes. The typeface, which is resolved into a bit pattern and is to be reproduced by the LED line, is read into shift register ICs via an 8-bit parallel data stream.

A pulse triggers the transfer of the bit pattern from the shift register to a data buffer memory. The individual luminescent diodes are switched on in accordance with the stored bit pattern via a further activation signal.

In the previous control circuits, there is the restriction that the same drive pulse is provided in amplitude and duration for all individual diodes, so that the spread of efficiency between the individual elements had to be as small as possible if the radiated energy of all controlled elements should be essentially the same . Due to this high requirement for the spread, the yield in the manufacture of the suitable and suitable luminescent diodes was relatively low, whereby an optimal uniformity of the radiated energy could not be achieved due to inevitable differences in the operating conditions for the individual components.

The invention is therefore based on the object of specifying a method for the periodic actuation of a plurality of radiation-emitting elements, with which it is achieved that the radiated energy of all actuated elements is essentially of the same size, without this being purchased through losses in yield in the manufacture of the individual components got to. This object is achieved in that differences in the radiation power of the individual elements, which are caused by variations in the efficiency of the elements or by different operating conditions, are compensated for in that the radiation-emitting elements are each operated with an individual pulse length which determines the total radiation duration , so that the radiated energy of all controlled elements is essentially the same size.

In the method according to the invention, in an advantageous development, the total radiation duration can be quantized in digital individual steps for each element. The commands for the individual steps are stored separately for each element in a memory. The memory content is determined, for example, after the completion of a diode row by measuring the individual elements. The quantization of the total radiation duration will advantageously be limited to the part of the total radiation duration that is required to compensate for the maximum difference in the radiation power of the individual elements. This means that all controlled individual elements are exposed to a basic radiation duration, which is supplemented by additional radiation durations for individual elements.

• Figur 1 zeigt eine geeignete Schaltungsanordnung zur Durchführung des erfindungsgemäßen Verfahrens.
• In Figur 2 sind die möglichen Einzelschritte für die Ansteuerung der Lumineszenzdioden dargestellt.
• Figur 3 zeigt für einen Ausschnitt von 5 aneinandergereihten Dioden die Datenmatrix im Schieberegister für die Ansteuerung der Diodenzeile.

The invention and its further advantageous embodiment will be explained in more detail below using an exemplary embodiment.

• Figure 1 shows a suitable circuit arrangement for performing the method according to the invention.
• FIG. 2 shows the possible individual steps for controlling the luminescent diodes.
• FIG. 3 shows the data matrix in the shift register for the control of the diode row for a section of 5 diodes arranged in a row.

According to FIG. 2, information which corresponds to the image pattern to be reproduced by the diode row DZ is called up, for example, from a computer at the data input DE. This digital information arrives via a buffer memory P1 at an input of the AND gate U, via whose output the shift register SR is loaded.

According to FIG. 3 it is assumed that for a section of 5 diodes D1-D5 strung together, the bit pattern 10110 is to be entered into the shift register via the data input DE. This means that the diodes D1, D3 and D4 should light up for a defined time interval, while the diodes D2 and D5 remain dark. The time interval during which the exposure pattern mentioned is emitted is denoted by t in FIG. 2a. x

There are now individual elements within the DZ series of diodes which scatter in efficiency and in which different operating conditions are also noticeable. This leads, for example, to the fact that individual diodes have already radiated the desired energy after a time t _{1 in} accordance with FIG. 2b, while other individual elements in accordance with FIGS. 2c, 2d and 2e only achieve the desired radiation energy in that they have additional time intervals t ₂ or t _{3 can be} controlled.

In the exemplary embodiment according to FIG. 2, the maximum total radiation duration for each element was divided into 3 individual steps. These consist of the basic radiation duration G during t ₁ and the additional _{radiation durations Z1 Z2} during times t ₂ and t ₃ . It goes without saying that the total radiation duration can be quantized according to requirements in any number of individual steps, but the circuit complexity increases with the number of individual steps.

The exemplary embodiment shown with three individual steps has proven itself and leads to an increase in the accuracy in the radiated power between the individual components by a factor of 3. The reason Radiation duration G was 850 μs in this exemplary embodiment, while the additional radiation durations Z ₁ and Z ₂ lasted 200 and 100 μs, respectively. The control amplitude SA was the same for all radiation phases.

After the completion of a diode row, it is determined for all individual elements which individual control steps are required for the individual element in order to achieve a uniform energy radiation across all elements. With four different total radiation durations, as represented by FIGS. 2b-2e, 2 bits are required to store the required information in the memory SP. The data content "00" then corresponds, for example, to the basic exposure G, the data content "01" corresponds to the basic exposure G and the additional exposure Z ₂ during the time t _21, the data content "10" corresponds to the basic exposure G and the additional exposure Z ₁ during the time t ₃₁ while the data content "11" is assigned to a diode for which all three exposure steps G, Z ₁ and Z _{2 are} required. This information is in each case associated with a special diode and stored in the memory SP according to FIG. 1.

In the embodiment of Figure 1, the second input of the AND gate U is linked to the output of an OR gate 0, one input of which is read the contents of the memory SP, while the other input is a command that the information, the Basic exposure or post-exposure supplies. The memory SP is controlled at the input N with a command which determines whether the 1st or 2nd required post-exposure Z ₁ or Z _{2 has been} called up, while the addressing counter AZ successively calls up the memory locations in the memory SP. The addressing counter is controlled via a clock input and a reset input.

The shift register SR is loaded in the usual way via the output of the AND gate. For this purpose, the clock pulse is also given to the shift register. A strobe pulse at the reset input of the addressing counter triggers the transfer of the bit pattern in the shift register to a data buffer memory P2. Via a further activation signal at the enable input of the buffer memory P2, the luminescent diodes in the row DZ are switched on in accordance with the bit pattern stored in the shift register. In the method according to the invention, the shift register SR is loaded and read out three times at a time interval t for an exposure process in order in this way to determine the individual total radiation power of each individual element. According to FIG. 3, it is assumed that in the case of the five diodes D1 to D5 strung together, the postexposure information is stored in the manner shown. Thereafter, no post-exposure is necessary for the diode D1, the diode D _2, the post-exposure Z ₂ for the diode D _3, the Nachbelichtungen Z ₁ and Z ₂ for the diode D ₄ and D _5, respectively, only the post-exposure Z. ₁

In the case of the basic exposure G there is a logic "1" at the exposure input of the OR gate, which consequently is also given to one input of the AND gate U. The information that is present at the data input DE is thus written into the shift register SR during the first loading process. In the exemplary embodiment in FIG. 3, this is the data sequence "10110", so that the controlled diodes D ₁ , D ₃ and D ₄ emit the basic exposure. The next time the shift register is loaded, the first bit in the memory SP is linked to the associated information at the data input DE at the AND gate U. In the example shown, this results in the shift register content "00110", so that the diodes D ₃ and D ₄ emit the post-exposure Z ₂ . During the third loading process of the shift register, the second information in the memory SP is linked to the associated information at the data input DE, so that the shift register content "00100" results in the selected exemplary embodiment, after which only the diode D ₃ also emits the further postexposure Z ₁ .

The shift register SR is reloaded in each case in the times between the individual exposure phases and, after all three exposure phases have been completed, a new bit pattern is called up at the data input DE. The memory SP preferably consists of an EPROM. The method according to the invention and the associated circuit arrangement are preferably used to control light-emitting diodes arranged linearly in a row, such as are supplied by TELEFUNKEN electronic under the type designations TPHM 8080 or TPAC 6050 and TPAC 6080. These diode rows are particularly suitable for the exposure of photoconductive layers or other light-sensitive materials.

Claims (9)

1) Method for the periodic control of several radiation-emitting elements, characterized in that differences in the radiation power of the individual elements (D), which are caused by scattering in the efficiency of the elements or by different operating conditions, are compensated for in that the radiation-emitting elements in each case be operated with an individual pulse length that determines the total radiation duration, so that the radiated energy of all controlled elements is essentially the same size. 2) Method according to claim 1, characterized in that the total radiation duration for each element is quantized in digital individual steps, the individual steps for each element being stored separately in a memory (SP). 3) Method according to claim 2, characterized in that the quantization is limited to the part of the total radiation duration, which is required to compensate for the maximum difference in the radiation power of the elements (D). 4) Method according to one of the preceding claims, characterized in that the maximum total pulse length consists of at least two partial pulses of different lengths, one partial pulse corresponding to the basic radiation duration provided for all controlled elements, while the remaining partial pulses to compensate for the differences in radiation power as individual additional radiation periods are provided for certain controlled elements. 5) Method according to one of the preceding claims, characterized by the use for controlling linearly arranged in a row (DZ) light-emitting diodes (D). 6) Method according to one of the preceding claims, characterized by the use for the exposure of photoconductive layers or other light-sensitive materials. 7) Circuit arrangement for performing the method according to any one of claims 1-4, characterized in that a logic (U, 0) is provided with which the data input signals for the elements with the signals retrieved from a memory (SP) for the partial pulses and that the commands for the individual radiation phases are entered into a shift register (SR) to be reloaded between the phases, which controls the individual elements (D) during the reading and thus determines the radiation pattern. 8) Circuit arrangement according to claim 7, characterized in that the partial pulse provided for all controlled elements and determining the basic radiation duration is directly linked to the data input signals, while the commands for the individual partial pulses, which determine the required additional radiation duration, are called up via a clocked addressing counter and linked to the pending data input signals at the AND gate (U).

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