Abstract:
The invention pertains to a driving device, for a light-emitting component, which can be universally used and is user-friendly. The driving device for a light-emitting component, particularly for a laser, includes an interface device for inputting a control signal selecting an operating mode of the component. It further includes a control device connected to the interface device, which drives the component with a predetermined operating-mode and temperature-dependent bias current and/or a predetermined operating-mode and temperature-dependent modulation current depending on the operating mode selected and depending on the temperature present at the component or on a temperature proportional thereto.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a driving device for driving a light-emitting component, particularly a laser. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of specifying a driving device for a light-emitting component which, in particular, can be used universally and, at the same time, exhibits a high degree of user friendliness. 
     Accordingly, according to the invention, a driving device for a light-emitting component, particularly for a laser, comprising an interface device for inputting control signals is provided. The control signals are used for selecting an operating mode of the light-emitting component. A control device connected to the interface device selects, depending on the operating mode selected at the interface and depending on the temperature present at the component—or depending on a temperature proportional to the component temperature, a corresponding or matching bias current value and/or modulation current value and applies to the light-emitting component a bias current and/or modulation current which corresponds to the selected bias current value or the selected modulation current value. 
     A significant advantage of the driving device according to the invention can be seen in the fact that it provides at least two different operating modes which can be selected by the user by applying corresponding control signals to the interface device. The driving device according to the invention can be used quite universally due to this possibility of selecting the operating mode. 
     A further essential advantage of the driving device according to the invention consists in that temperature changes which, as is known, can have a considerable influence on the characteristic of light-emitting components, are automatically taken into consideration by the driving device because the driving takes place both in dependence on the selected operating mode and in dependence on the prevailing temperature. 
     A temperature control can be effected in a particularly simple and thus advantageous manner if the driving device exhibits a temperature sensor by means of which the temperature of the light-emitting component or a temperature proportional thereto is measured. 
     For example, the temperature control can be effected “indirectly” in that the temperature drift of an amplifier circuit contained in the control device or the temperature characteristic of a thermally sensitive component—for example a temperature-dependent resistor—is used (as temperature sensor). 
     The driving device advantageously exhibits a storage device in which in each case a drive table is stored at least for two different operating modes of the light-emitting component, each of the drive tables in each case containing a bias current value and/or a modulation current value for at least two measured temperature values. 
     The storage device is preferably connected to the control device; the control device is then constructed, for example, in such a manner that it reads out the in each case associated bias current value and/or modulation current value, stored in the drive table, depending on the selected operating mode and depending on the measured temperature value of the temperature sensor, and drives the component with a bias current corresponding to the bias current value and/or a modulation current corresponding to the modulation current value. 
     According to an advantageous embodiment of the driving device according to the invention, it is provided that the temperature sensor is connected to the storage device and the measured temperature value of the temperature sensor is transferred from the temperature sensor to the storage device. The storage device is constructed in such a manner that it exclusively transfers to the control device those bias current values and/or modulation current values which correspond to the respective measured temperature value. In this embodiment of the storage device, the “temperature correction” in the drive to the light-emitting component is thus ensured on the side of the storage device. Thus, the control device can only read out the bias current values or modulation current values corresponding to the in each case prevailing temperature for the individual operating mode from the storage device. 
     In order to ensure that the driving device can be adapted to various operating modes in a particularly simple and thus advantageous manner, it is considered to be advantageous if the storage device exhibits a separate storage area for each drive table, particularly in each case a separate memory chip. Thus, the driving device can be adapted very simply to the operating modes desired in each case by changing storage areas or chips by addressing a suitable storage area or connecting a suitable memory chip to the storage device depending on the desired operating mode. 
     In addition, it is considered to be advantageous if the temperature sensor is in each case connected to each storage area or memory chip of the storage device. If the temperature sensor, for example, outputs a digital output signal as output signal, this digital output signal can be used directly or indirectly for determining the memory space or memory cell in which the bias current value or modulation current value, belonging to the respective temperature, for the light-emitting component is stored. In this case, therefore, the output signal of the temperature sensor directly specifies the associated memory location at which the desired information for driving the light-emitting component is stored. 
     Correspondingly, the storage areas or memory chips in each case preferably have a connection at which the output signal of the temperature sensor can determine the storage area which should be readable by the control device. 
     According to another advantageous development of the driving device according to the invention, it is provided that the control device is connected to the temperature sensor and the measured temperature value is transferred from the temperature sensor to the control device. In this embodiment of the invention, the control device, therefore, reads out the respective measured temperature value of the temperature sensor and then accesses, individually for each operating mode, the corresponding storage cells of the storage device in which the current values, that is to say modulation current value and/or bias current value matching the respective measured temperature value and the respective operating mode, are stored. 
     In a particularly simple and thus advantageous manner, a light-emitting component can be driven by means of the driving device if the control device comprises a D/A converter and a driver which is connected to the light-emitting component. The driver then drives the light-emitting component with a modulation current and/or a bias current which is predetermined by the D/A converter of the control device. The driver preferably contains an operational amplifier since operational amplifiers have a very high impedance at the input and have a very low current consumption. The D/A converter of the control device is preferably connected to an input of the operational amplifier. 
     To ensure that there are other possibilities for the user to influence the driving of the light-emitting component, it is considered to be advantageous if the other input of the operational amplifier is connected to the programmable resistor network which can be controlled by control signals and/or control bits. The electrical characteristic of the operational amplifier can then be adjusted or influenced by applying corresponding control signals or control bits to the programmable resistor network. 
     If, for example, it should be possible for the user to influence or correct the “feedback path” formed by a monitor diode of the light-emitting component, it is considered to be advantageous if the programmable resistor network is connected to a monitor diode of the light-emitting component. 
     The operational amplifier of the control device is preferably connected in such a manner that the D/A converter of the control device is connected to the negative input of the operational amplifier and the programmable resistor network is connected to the positive input of the operational amplifier. 
     The light-emitting component can be, for example, light-emitting diodes, edge-emitting lasers or surface-emitting lasers. 
     In addition, the invention is based on the object of specifying a method for driving a light-emitting component which can be used quite universally and is very user friendly. 
     With respect to the advantages of the method according to the invention and its advantageous embodiments, reference is made to the above statements in conjunction with the driving device according to the invention. To explain the invention, 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a first exemplary embodiment of a driving device according to the invention by means of which the method according to the invention can also be carried out and 
         FIG. 2  shows an exemplary embodiment of a driver for the driving device according to  FIG. 1 ; and 
         FIG. 3  shows a further exemplary embodiment of a driving device. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a driving device  10  which comprises a temperature sensor  20 , a storage device  30 , an interface device  40  and a controller  50 . 
     The storage device  30  has a first memory chip  100 , a second memory chip  110  and a third memory chip  120 . In each of the memory chips  100 ,  110  and  120 , respectively, a drive table is in each case stored which specifies how a laser  200  connected to the drive device  10  is to be driven. 
     The memory chips  100 ,  110  and  120  in each case have a temperature input which is connected to an output A 20  of the temperature sensor  20 . The temperature inputs of the three memory chips  100 ,  110  and  120  bear the reference designations T 100 , T 110  and T 120 , respectively, in FIG.  1 . 
     The controller  50  has a multiplexer  200 , the multiplexer inputs E 200   a , E 200   b  and E 200   c  of which are connected to outputs of the memory chips  100 ,  110  and  120 . Actually, one input E 200   a  of multiplexer  200  is connected to the output A 100  of the memory chip  100 . A further input E 200   b  of multiplexer  200  is connected to an output A 110  of memory chip  110 . An additional input E 200   c  of multiplexer  200  is preceded by an output A 120  of memory chip  120 . 
     In addition, the multiplexer  200  has a control input S 200  which is connected to an output A 40  of the interface device  40 . The interface device  40  is formed by a controller, the input E 40  of which forms the interface E 10  of the driving device  10  to the outside. Applying corresponding control signals or control bits to input E 40  of the interface device  40  allows control signals for driving the multiplexer  200  to be fed into the driving device  10 . 
     An output A 200  of multiplexer  200  is connected to an input E 300  of a D/A (digital/analog) converter which is followed by an input E 400  of a driver  400 . The output A 400  of the driver  400  is connected to the laser  150 . 
     The driving device  10  according to  FIG. 1  is operated as follows: 
     Firstly, a drive table which specifies how the laser  150  is to be driven in accordance with a first operating mode is stored in the first memory chip  100 . The drive table contains in each case a bias current value  I   B  and a modulation current value  I   M  for at least two temperature values. The drive table advantageously exhibits not only current values for two temperature values but for a multiplicity of temperature values. The greater the number of temperature values stored in the drive table, the better the laser  150  can be controlled in the case of temperature changes. 
     A drive table is also stored in memory chip  110 . This drive table, however, is provided for another operating mode than the drive table which is stored in the first memory chip  100 . The drive table in the second memory chip  110  also contains bias current values  I   B  and modulation current values  I   M  which are in each case associated with temperature values. Thus, temperature-dependent drive parameters which can be used for driving the laser  150  can also be taken from the drive table of the second memory chip  110 . 
     The third memory chip  120  correspondingly also contains a drive table in which bias current values  I   B  and modulation current values  I   M  are stored for various temperature values. The drive table of the third memory chip  120  refers to a third operating mode of the laser  150  which differs from the operating modes stored in the drive tables of the two memory chips  100  and  110 . 
     When the driving device  10  is taken into operation, the temperature sensor  20  will output at its output A 20  a temperature value which specifies the respective temperature of the laser  150  or a temperature proportional thereto. This temperature value T passes to the temperature inputs T 100 , T 110  and T 120  of the three memory chips  100 ,  110  and  120 . 
     The memory chips  100 ,  110  and  120  are designed in such a manner that the temperature value T present at the respective temperature input T 100 , T 110  and T 120 , respectively, directly specifies a storage area or a storage cell which can be read out at the output via outputs A 100 , A 110  or A 120 , respectively. 
     If then an operating mode B is specified from the outside via the interface device  40 , the interface device  40  generates an operating mode control signal SB specifying the respective operating mode. This operating mode control signal SB is transferred to the control input S 200  of the multiplexer  200  which thereupon selects one of the three memory chips  100 ,  110  or  120 , respectively. Thus, the respective memory chip is selected by the operating mode control signal SB. 
     As explained above, the memory chips  100 ,  110  and  120  in each case contain a drive table which has been predetermined for in each case one operating mode. If, for example, the operating mode control signal SB contains the information that the first operating mode has been selected, the multiplexer  200  will access memory chip  100  in which the drive table for the first operating mode is stored. 
     The multiplexer  200  will correspondingly access the second memory chip  110 , the drive table of which contains the drive parameters for the second operating mode, if the second operating mode has been selected. 
     If the operating mode control signal SB specifies the third operating mode, the multiplexer  200  will address memory chip  120  in which the drive table and operating parameters for the third operating mode are stored. 
     In the text which follows, it is assumed that the first operating mode has been selected. The multiplexer  200  will, therefore, address or read out the first memory chip  100 . It is only possible to read out the storage area which is predetermined by the measured temperature value T present at the temperature input T 100 . The multiplexer  200  will thus read out a bias current value  I   B  and a modulation current value  I   M  which corresponds to the first operating mode at the temperature T detected by the temperature sensor  20 . 
     Multiplexer  200  forwards the current values  I   B  and  I   M  to the D/A converter  300  which generates an analog drive signal UM for the driver  400  from the digital current values  I   B  and  I   M . At output A 400  of the driver  400 , an output voltage or output potential is then provided which generates the desired bias current  I   B  and the desired modulation current  I   M  in the laser  150 . 
     The multiplexer  200  will correspondingly access the drive table stored in the second memory chip  110  if the second operating mode is predetermined via the interface device  40 . 
     If the third operating mode is required, the drive table in the third memory chip  120  is accessed. 
       FIG. 2  shows an exemplary embodiment of the driver  400  according to FIG.  1 . 
     It can be seen in  FIG. 2  that input E 400  of the driver  400  is formed by a positive input of an operational amplifier  600 . The negative input of the operational amplifier  600  is connected to a terminal  610  of a programmable resistor network R Adj , the other terminal  620  of which is connected to ground. 
     Moreover, the negative input of the operational amplifier  600  is connected to a monitor diode  700  of the laser  150 , which is connected to the supply voltage V DD . The monitor diode  700  generates a monitor current I MCD  which flows to ground via the programmable resistor network R Adj . 
     Depending on the voltage U dropped across the programmable resistor network R Adj , a potential difference ΔU which is corrected to “0” by the operational amplifier occurs between the two inputs of the operational amplifier  600 . This correction leads to an output voltage U A  at the output of the operation amplifier  600  which is present as base-emitter voltage at a transistor T 1 . The collector terminal of transistor T 1  is connected to the laser  150  so that the laser  150  is driven by the operational amplifier  600  by means of transistor T 1 . 
     The programmable resistor network R Adj  can be, for example, a resistor network as described in detail in the patent application No. 10/454,021, particularly in conjunction with  FIGS. 3  to  5 . 
       FIG. 3  shows a further exemplary embodiment of a driving device  10 . In distinction from the driving device  10  according to  FIG. 1 , the temperature sensor  20  in the exemplary embodiment of  FIG. 3  is connected directly to the control device  50 , namely with a microprocessor  800  of the control device  50  . This microprocessor  800  replaces the multiplexer  200  as described in conjunction with  FIGS. 1 and 2 . 
     Microprocessor  800  has the task of reading out the temperature sensor  20  and correspondingly reading out the storage device  30  depending on the operating mode B predetermined at the interface via interface  40  and depending on the measured temperature value T determined by the temperature sensor  20 . 
     In the storage device  30 , the drive tables  900 ,  910 ,  920  (designated as registers set I to III in  FIG. 3 ) required for driving the laser  150  are stored. 
     As soon as the microprocessor has read out the current values  I   B  and  I   M , required for driving the laser  150 , from the storage device  30 , it correspondingly drives the D/A converter  300  in such a manner that the desired current flows through the laser  150 .