DE102010031217A1 - Laser module for projection applications and method for operating such a laser module - Google Patents

Abstract

The present invention relates to a laser module for projection applications with several channels, a control circuit being provided for controlling the laser power for each channel. On the one hand, a setpoint value of the brightness of the respective channel is fed to the respective control circuit, and on the other hand an actual value of the brightness, which is correlated with the signal which is output by a photodiode (PDR) which is assigned to the respective channel (R). To compensate for the channel crosstalk of a channel (R) by electrical means, either the setpoint (VoriR) of the brightness supplied to the control loop or the actual value (RKmodR) of the brightness supplied to the control loop is modified by at least one coupling signal (KGR) that is from one of the other channels (G) comes. The invention also relates to a method for operating such a laser module.

Description

Technical area

The present invention relates to a laser module for projection applications, comprising a drive device with an input for coupling to a source of useful data to be projected, wherein the payload to be projected comprise at least a first portion of a first wavelength and a second portion of a second wavelength, at least a first An output for providing a setpoint brightness of the first wavelength, and at least a second output for providing a setpoint brightness of the second wavelength. The laser module further comprises at least one laser diode for emitting radiation of the first wavelength and at least one second laser diode for emitting radiation of the second wavelength, at least one first photodiode having an output for providing an actual value of the brightness, wherein the first photodiode so to the the first laser diode is arranged such that at least a portion of the radiation emitted by the first laser diode during operation is detectable by the first photodiode, and at least one second photodiode having an output for providing an actual value of the brightness, wherein the second photodiode so arranged to the second laser diode in that at least a portion of the radiation emitted by the second laser diode during operation is detectable by the second photodiode, at least one second laser driver device associated with the first wavelength and associated with the second wavelength, each laser driver device following s comprises: a first input coupled to the associated output of the drive device, a second input coupled to the output of the associated photodiode, an output for providing a drive signal to the associated laser diode, a variable gain amplification device is coupled between the first input and the output of the respective laser driver device, and an evaluation device having a first input, which is coupled for supplying a desired value of the brightness with the first input of the laser driver device, a second input, which is for supplying an actual value of the brightness with the coupled to the second input of the laser driver device, and an output for adjusting the gain of the associated amplifying device, wherein the evaluation device is designed to determine the amplification factor for the associated amplifying device, wherein the di e evaluation device is further designed to subtract a second evaluation signal from a first evaluation signal in the determination of the gain factor, wherein the first evaluation signal comprises the signal at the first input of the evaluation device, wherein the second evaluation signal comprises the signal at the second input of the evaluation device. The invention also relates to a method for operating such a laser module.

State of the art

The present invention is described below using the example of a red-green-blue (RGB) laser module, that is, a laser module in which cooperate three laser diodes and a resulting by emitting a laser beam in the red, green and blue wavelength range Generate overall jet with almost arbitrary adjustable hue. Independently of this, the present invention can also be used in other laser modules, for example a laser module, which comprises only two lasers which emit radiation in a different wavelength range. The wavelength range can not only be in the visible range, but also, for example, in the infrared or ultraviolet range.

It is known to use photodetectors in such a laser module for stabilizing the respective laser power, or the color locus of the resulting beam. 1 shows in this context an arrangement known from the prior art. This includes a source 12 , in which the payload to be projected is in digital form. In the present case, these useful data comprise a first component in the red wavelength range, a second component in the green wavelength range and a third component in the blue wavelength range. This image data becomes a driving device 14 supplied, the three outputs, wherein at the first output a target value of the brightness in the red wavelength range, at the second output a target value of the brightness in the green wavelength range and at the third output a target value of the brightness in the blue wavelength range is provided. These data are from the drive device 14 via respective inputs E _1R , E _1G and E _{1B of} a respective laser driver device 16R . 16G such as 16B fed.

The interior of such a laser driver device is for clarity only for the laser driver device 16R shown. On the right side of the respective laser driver device 16R . 16G . 16B is connected to a respective output A _R , A _G , A _B, a corresponding laser diode LD _R , LD _G , LD _B connected. In this case, the laser diode LD _{R is} designed to emit radiation in the red wavelength range. Corresponding is designed the laser diode LD _G , radiation in the green wavelength range and the laser diode LD _B designed to emit radiation in the blue wavelength range. Each laser diode LD _R , LD _G , LD _B is assigned a respective photodiode PD _R , PD _G , PD _B , each photodiode PD _R , PD _G , PD _B having an output for providing an actual value of the brightness associated with the corresponding laser driver device is coupled via an input E _2R , E _2G , E _2B . In order to provide a corresponding signal, the respective photodiode PD _R , PD _G , PD _{B is arranged} to the respective laser diode LD _R , LD _G , LD _B such that at least a portion of the light emitted by the respective laser diode during operation of the respective Photodiode PD _R , PD _G , PD _{B is} detectable.

The three laser driver devices 16R . 16G . 16B will be described below using the example of the laser driver device 16R described: With the input E _1R is first a D / A converter 18R coupled, which _provides at its output A _18R1 in analog form, a target value of the brightness of the portion of the image data, which are in the red wavelength range. To generate a drive signal at the output A _R for the laser diode LD _R , moreover, the laser threshold must be taken into account. For this purpose, the D / A converter provides 18R at its output A _18R2 a corresponding offset _R ready. The signal at the output A _18R1 is in an amplification device 20R according to one of an evaluation device 22R multiplied by the gain factor V _R provided by the D / A converter. Subsequently, in an addition device 26R at the output A _{18R2 of} the D / A converter 18R added offset _R added. This sum signal is then in an output stage 28R further amplified and then provided via the output A _{R of} the laser diode LD _R available.

The already mentioned evaluation device 22R is via an input E _22R1 that at the output A _{18R1 of} the D / A converter 18R provided via an input E _22R3 of the output A _{18R2 of} the D / A converter provided value Offset _R and at the input E _22R2 that at the input E _{2R of} the laser driver device 16R adjacent, supplied from the photodiode PD _R , in an amplification stage 30R amplified signal supplied. The evaluation device 22R accordingly receives via the first input E _22R1 a signal which is correlated with the desired value of the brightness in the red wavelength range and via the second input E _22R2 a signal which is correlated with the actual value of the brightness in the red wavelength range. On the internal processing, in the evaluation device 22R takes place, for example, to take into account the laser threshold of the photodiode PD _R , will be discussed in more detail in connection with the drawings showing embodiments of the present invention. In connection with 1 is therefore initially only of importance that the evaluation device 22R is designed to determine the difference between the signal at input E _22R1 and at input E _22R2 to determine the gain V _R.

How out 1 is apparent, each laser diode LD _R , LD _G , LD _{B is} a single photodetector in the form of a photodiode PD _R , PD _G , PD _B assigned. The signal measured by the respective photodiode PD _R , PD _G , PD _B thus serves as a measure of the laser power emitted by the laser module onto a projection surface. In this way, the output from the respective photodiode PD _R , PD _G , PD _B signal for a regulation of the laser power to a desired level, regardless of environmental conditions, such as temperature fluctuations, can be used. In practical implementations, however, it has been found that, despite this regulation, the actual value of the color coordinates often deviates from the nominal value.

2 For example, in a CIE standard color chart, this shows the actual location O _I and the desired location O _{S of} the overall beam. As can be clearly seen, the actual location O _I lies outside the so-called MacAdams ellipse with five times the half-axis length of the standard MacAdams ellipse. This means that the change in light color can be clearly perceived by the human eye.

Presentation of the invention

The object of the present invention is therefore to further develop the laser module mentioned at the outset as well as the method mentioned at the beginning in such a way that chromaticity shifts can be largely prevented.

This object is achieved by a laser module having the features of patent claim 1 and by a method having the features of patent claim 14.

The present invention is based on the finding that the color locus shift is based on the fact that the three control circuits influence one another. For example, that of the photodiode PD _R , which is designed to detect radiation that is in the red wavelength range, influenced by the power emitted by the two laser diodes LD _G , LD _B , the radiation in the green or blue wavelength range delivered. This influence is referred to as channel crosstalk, whereby a distinction can be made between optical and electronic crosstalk.

The considerations leading to this realization will be described in more detail below, where LPR, LPG, LPB denote the laser power of the optical output power emitted by the red, the green and the blue laser diode to the respective photodiode. LPR, LPG, LPB are expressed as a percentage of the respective maximum output level. UPDR, UPDG, UPDB denotes the signal level measured by the respective photodiode.

The following equations describe the general case that the three channels influence each other: UPDR = LPR * 1 + LPG * XT_GR + LPB * XT_BR UPDG = LPR * XT_RG + LPG * 1 + LPB * XT_BG UPDB = LPR * XT_BR + LPG * XT_GB + LPB * 1

XT_GR:

der prozentuale Anteil der Leistung LPG, welcher auf die Photodiode des roten Kanals fällt,

XT_BR:

der prozentuale Anteil der Leistung LPB, welcher auf die Photodiode des blauen Kanals fällt,

XT_RG, XT_BG,

... entsprechend.

The factors (= crosstalk coefficients) mean the following:

XT_GR:

the percentage of power LPG falling on the photodiode of the red channel

XT_BR:

the percentage of power LPB falling on the photodiode of the blue channel,

XT_RG, XT_BG,

... corresponding.

The above equation can be represented as a matrix equation:

Exemplary typical values for the crosstalk coefficients are:

As measurements have shown, the maximum expected value for the crosstalk coefficients is approximately 10%.

The laser module according to 1 is now calibrated so that at full modulation of the three laser diodes, ie LP _R = 100%, LP _B = 100%, LP _G = 100%, a certain white point, such as D65, is generated.

In the following, the case will be examined that of the driving device 14 output digital data divided by the respective wavelength ranges so that the image content represents a white area. That is, the corresponding laser driver devices 16R . 16G . 16B the laser diodes LD _R , LD _G , LG _{B will} be controlled so that the signal level delivered by the respective photodiode PD _R , PD _G , PD _B is set as follows:

By converting the matrix equation (left-sided multiplication with the inverse matrix), the resulting laser powers result in:

For the typical case of the crosstalk coefficients given above by way of example:

ergibt sich somit im Mittel eine Absenkung des emittierten Lichtflusses und eine relative Veränderung der Leistungen LPR, LPG, LPB zueinander. Mit anderen Worten reduziert die Regelung aufgrund des Übersprechens das eigentliche Ansteuersignal. Dies führt dazu, dass die jeweiligen Ansteuerpegel fälschlich zu weit abgesenkt werden und daher zu wenig Leistung bei der entsprechenden Laserdiode ankommt.Opposite the nominal values

Thus, on average, there is a lowering of the emitted light flux and a relative change in the powers LPR, LPG, LPB relative to one another. In other words, the control reduces the actual drive signal due to crosstalk. As a result, the respective drive levels are falsely lowered too far and therefore too little power arrives at the corresponding laser diode.

Since the three laser beams in the laser module are combined into one beam, the change in relative laser powers results in a color locus drift of the resulting combined radiation. This leads to the differences between the actual value O _I and the target value O _{S of} the color locus, as in 2 shown.

From this follows the finding that in a known from the prior art laser module according to 1 However, the channel crosstalk in combination with activated control of the laser power by the resulting change in light color leads to a significant impairment of color stability.

According to the invention, the channel crosstalk is compensated by weighted coupling of the color channels in the control electronics. The weighting of the mutual admixture is chosen so that it quantitatively corresponds to the crosstalk of the channels. The factors of weighting are determined for each laser module. The modules are configured according to this weighting.

According to the invention, the evaluation device of the first laser driver device for supplying at least one coupling signal is therefore coupled to at least the second laser driver device, wherein the evaluation device in the first laser driver device is designed to determine the amplification factor for the first amplifying device, taking into account furthermore the at least one coupling signal.

In this way, the variables supplied to the evaluation device are influenced in such a way that the effect of channel crosstalk no longer affects the manipulated variable, that is, the signal driving the respective laser diode LD _R , LD _G , LD _B.

In this context, it should be mentioned that methods are known to prevent or avoid channel crosstalk. For example, for this purpose, the distance of the respective emitting elements is increased. Thus, it is possible to reduce the effect, since the optical power of each coupling element decreases by the increased distance. However, this method is only conditionally suitable for compensating the effect on the one hand and, on the other hand, counteracts the need for increasing integration. Another approach to prevent crosstalk is to isolate the photodetectors from the light of the other channels by the use of optical elements, such as dielectrically coated glasses. The filters are designed so that the light of the detector associated laser diode can happen (high transmission) that light with the wavelength of the adjacent channels, however, blocked (high reflection or high absorption). Such a coating can for example also be applied to the photodiodes themselves. However, this approach has the disadvantage that three further optical elements must be integrated into the structure. The approach to coat the photodetectors themselves with a filter layer has the disadvantage that then the photodetectors are no longer interchangeable, that is, the logistical effort in production stalls, as always photodetectors each wavelength range must be kept in stock.

According to the invention, the compensation of the channel crosstalk therefore takes place electronically. Thus, no mechanical measures are necessary, which reduces the size of a laser module according to the invention. Furthermore, by the present invention, a complete compensation can be achieved, whereas mechanical measures only lead to a reduction of said effect.

A preferred embodiment is characterized in that here the laser driver device comprises a D / A converter device which is coupled between the associated output of the drive device and the associated amplification device. This D / A converter device can be designed not only to perform a simple D / A conversion, but also a corresponding preprocessing, for example, to determine from the signals at the input of the D / A converter device, the offset that at the output of the D / A converter device analog present image data after the gain is added to take into account the laser threshold.

In a first variant of a laser module according to the invention, the signal at the input of the D / A converter device of the second laser driver device represents the at least one coupling signal. Accordingly, the image data signal assigned to the second wavelength range is supplied in its digital form to the first laser driver device.

In a second variant, the signal at the output of the D / A converter device of the second laser driver device represents the at least one coupling signal. In this case, the signal associated with the image data of the second wavelength range is supplied in analog form to the first laser driver device.

In these two variants, the evaluation device of the first laser driver device is preferably designed to form the first evaluation signal by adding the signal at its first input and the coupling signal multiplied by a first predefinable coupling factor. In other words, in these two variants, once on digital, once on the analog side, modified the setpoint of the brightness supplied to the evaluation device. The evaluation device therefore compares the actual value of the brightness supplied by the photodiode with a modified setpoint value of the brightness. By modifying the setpoint of the brightness, the channel crosstalk is taken into account.

In a third variant, the signal at the second input of the evaluation device of the second laser driver device represents the at least one coupling signal. The coupling signal for the first laser driver device is thus formed by the signal which the second laser driver device receives from its associated photodiode.

In this context, the evaluation device of the first laser driver device is preferably designed to form the second evaluation signal by subtracting the coupling signal multiplied by a second predeterminable coupling factor from the signal at its second input. In this case, the evaluation device of the first laser driver device compares the unmodified desired value of the brightness with a signal in which the signal coupled to the evaluation device by the first laser driver device has been modified as a result of the signal supplied to the evaluation device of the second laser driver device by the first laser driver device their associated photodiode was supplied.

This third variant can be implemented particularly advantageously if the evaluation devices of all three channels are implemented in an integrated circuit. As a result, the photocurrents can be mixed alternately in a particularly simple manner.

Accordingly, in this third variant, the evaluation device preferably comprises a subtraction device. Particularly preferably, such a subtraction device comprises at least one current mirror device, wherein the current mirror device comprises at least a first transistor which is coupled to the signal at the second input of the evaluation device, and at least one second transistor which is coupled to the signal at the second input of the evaluation device of the second laser driver device. By adopting such a procedure, the second predefinable coupling factor can be defined by geometry parameters of the at least one first transistor and the at least one second transistor. This eliminates a calculation using a digital unit. This results in a cost savings on the one hand and in a minimum space requirement and a high processing speed on the other. As a result, particularly high levels of integration can be achieved in a cost-effective manner.

Preferably, the first transistor and / or the second transistor is realized by an adjustable transistor array. In this case, each transistor array may include a plurality of individual transistors, wherein each individual transistor is associated with an electronic switch to switch a predetermined number of the plurality of individual transistors for setting the second predetermined coupling factor in parallel. In this case, a so-called thermometer coding can be used.

In the foregoing, embodiments have been described with reference to a laser module comprising two channels, a first channel for a first wavelength and a second channel for a second wavelength. In general, however, a laser module according to the invention has at least two, preferably two or three laser driver devices, each laser driver device being coupled to the at least one further laser driver device for supplying a coupling signal / coupling signals, each laser driver device being designed to determine the amplification factor for the laser driver device its associated amplification device to take into account the coupling signal / the coupling signals of the at least one further laser driver device.

Further preferred embodiments emerge from the subclaims.

The preferred embodiments presented with reference to the laser module according to the invention and their advantages apply correspondingly, as far as applicable, to the method according to the invention.

Brief description of the drawings

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Show it:

1 a schematic representation of a known from the prior art laser module;

2 a schematic representation of a CIE standard color chart showing the color locus shift due to channel crosstalk;

3 a schematic representation of a first embodiment of a laser module according to the invention;

4 in schematic representation a section of the in 3 illustrated embodiment in a slightly modified representation;

5 a modification of the in 4 presented details of in 3 illustrated embodiment of a laser module according to the invention according to a first variant;

6 on the basis of in 4 presented details of in 3 illustrated embodiment of a laser module according to the invention a second variant;

7 a detail of in 3 illustrated embodiment of a laser module according to the invention according to a third variant;

8th a schematic representation of the generation of a coupling factor by means of a current mirror for in 7 illustrated variant; and

9 a development of the current mirror according to 8th forming the transistors T1 and / or T2 as a transistor array.

Preferred embodiment of the invention

In the different drawings, the same reference numerals are used for identical and identical components. In particular, those with reference to 1 introduced reference numerals also used for the other figures and not reintroduced.

This in 3 schematically illustrated embodiment of a laser module according to the invention differs from the in 1 illustrated, known laser module characterized in that the evaluation device 22R of the red channel, a coupling signal K _GR from the laser driver device of the green channel and a coupling signal K _GB from the laser driver device 16B the blue channel is supplied. The evaluation device 22R is designed, the gain factor V _R for the amplifying device 20R taking into account the coupling signals K _GR and K _BR to determine.

In the following, three different variants are shown by way of example in more detail, which process these coupling signals to take account of the channel crosstalk and in which different coupling signals are used.

First, however, it will open 4 With reference to the example of the laser driver device 16R for the red channel a slightly modified view of a section of the in 3 illustrated embodiment of a laser module according to the invention is selected. In contrast to the representation of 3 is in the presentation of 4 the evaluation device 22R divided into a first part 22Ra which provides at its output a feedback signal RK _R , and in a second part 22Rb that with the D / A converter 18R is summarized, and at its output A _{22VR provides} the gain V _R.

This combined device 18R / 22Rb therefore has three outputs, wherein at the output A _18R2 the offset component offset _R , at the output A _18R1 an analog representation V _{oriR of} the image data in the red wavelength range and at the output A _22VR the gain V _{R is} provided. About an input of the device 18R / 22Rb the signal RK _R at the output A _{22R of} the evaluation device 22R made available.

Like the presentation of 4 continues to be seen, is in the evaluation device 22Ra first, the sum of the offset component offset _R and the signal V _oriR at the output A _{18R1 of} the device 18R / 22Rb formed and from this sum the signal at the input E _{22R2 of} the evaluation device 22Ra subtracted. At the output A _{22R of} the evaluation device 22Ra Accordingly, a feedback signal RK _R , which results in the device 18R / 22Rb is considered to determine the current value of the gain V _R. The aim of this control loop is to achieve that the signals at the input of the subtraction device in the evaluation device 22Ra are identical.

The following figures now show details of the structure of 4 for compensating the channel crosstalk. Without consideration of the channel crosstalk, as already mentioned above, the optical output power of the respective laser diode would be adjusted by the control circuit such that the sum of the coupling and the actual electrical stimulation in turn coincides with the image data signal. However, with this, the actually emitted optical power does not correspond to that given by the image data signal, thus adversely affecting the image quality.

In the variants of the in 3 illustrated embodiment of a laser module according to the invention is essential that the proportion of channel crosstalk between the respective channels is approximately constant. This means, for example, that always 5% of the optical power of the red laser diode is detected by means of the photodiode of the blue channel. This assumption is fulfilled in practice in the vast majority of cases.

Based on this relationship, for example, the results in 5 illustrated first variant to compensate for the effect of the channel crosstalk electronically:
The addition device of the evaluation device 22R a modified image data _signal V _{modR is} supplied, that is, a modified desired value of the brightness of the radiation to be emitted by the laser diode of the red channel. The modification takes place in the 5 illustrated variant on the digital side within the device 18R / 22Rb instead of. The modified image data _signal V _modR is formed by V _modR = V _oriR + (V _oriB + Offset _B ) · CT _BR + (V _oriG + Offset _G ) · CT _GR

Subsequently, a D / A conversion (DAC) takes place so that the signal V _{modR of} the evaluation device 22Ra can be provided in analog form. In this equation, CT _BR denotes the crosstalk factor to account for the channel crosstalk from the blue to the red channel. Similarly, DT _GR denotes the crosstalk factor to account for channel crosstalk from the green to the red channel.

This compares the evaluation device 22Rb of the red channel, the output signal of the red laser diode associated with the photodiode, which is exaggerated by the over-coupling, with the image signals increased by the corresponding amounts of image data signal.

At the in 6 variant shown in the in 5 illustrated variant on the digital side of the device 18R / 22Rb applied method now on the analog side instead. In other words, in order to take into account the channel crosstalk, the respective image data signals are thus processed in their analog form, wherein 6 the influence of the blue and green channel on the red channel, the influence of the red and green channel on the blue channel and the influence of the red and blue channel on the green channel. The three upper signals seen on the left side of the illustration are from the device 18R / 22Rb , the middle three signals from the device 18B / 22bb and the bottom three signals from the device 18G / 22GB ,

As can be readily _appreciated , the equation shown above for calculating the signal V _modR also applies to the in 6 illustrated variant of an embodiment of a laser module according to the invention.

Also in the presentation of 6 the image data signal which has been increased by the offset is again increased by the crosstalk signal. The crosstalk signals of the adjacent channels, here blue and green, are generated by multiplying the respective offset image data signals by the weighting factors CT _BR and CT _GR .

This variant is particularly suitable if the evaluation devices of all three channels are converted into an integrated circuit, in particular a chip.

7 shows a third variant of in 3 illustrated embodiment of a laser module according to the invention. This is based on the assumption that the evaluation devices of all three channels are implemented in an integrated circuit. The currents coming from the photodiodes are mixed alternately. Using the example of the red channel, the photocurrents of the green and blue channels weighted with the crosstalk coefficients are therefore subtracted from the photocurrent of the red channel.

While in the variants of 5 and 6 the setpoint of the brightness has been modified, is in the variant according to 7 the actual value of the brightness is modified to take account of the channel crosstalk. For this purpose, it is particularly preferred that the photodiode current of the photodiode of the respective channel via a so-called, in 8th shown, diode-connected transistor to lead. Using the example of a field effect transistor, the gate terminal is connected to the drain terminal in a diode-connected transistor. Although NMOS trasistors are used as examples in the present case, the invention can of course also be implemented with NPN, PNP or PMOS transistors.

wobei K_T2 und K_T1 entsprechende Geometrieparameter der Transistoren T1, T2 repräsentieren. Mit anderen Worten kann das Verhältnis zwischen Eingangsstrom I_e und Ausgangsstrom I_a über die Geometrie der beiden Transistoren T1, T2 festgelegt werden.At the in 8th illustrated example of a current mirror corresponds to the ratio between input current I _e and output current I _a following relationship:

where K _T2 and K _{T1 represent} corresponding geometry parameters of the transistors T1, T2. In other words, the relationship between input current I _e and output current I _{a can be determined} via the geometry of the two transistors T1, T2.

Regarding 7 Accordingly, by choosing the geometry parameters, the crosstalk coefficients can be taken into account. The respective mirrored current is correspondingly weighted via the transistors T _CTxx , where x stands for B, R or G, subtracted from the actual, the channel associated photodiode current. In an equation, it follows: RK _modR = RK _R -T _CTBR × RK _B -T _CTGR × RK _G , where RK _{modR represents} the modified feedback signal of the red channel.

Thus, the photocurrent of a photodiode is weighted in each case mirrored in the other photodiode branches, whereby the current flowing through the actual, the channel associated so-called sense transistor T _Sx , according to the crosstalk coefficients is reduced.

As already mentioned, the weighting can be done by the geometry of the transistors. As a result, however, it is determined by hardware. A particularly simple variant, however, to keep the crosstalk coefficients variable, is by a with respect to the 9 presented, configurable transistor array allows. This means that each coupling _transistor T _CTxx used to feed in a coupling _{signal is represented} by such an array. 9 shows by way of example the transistor T _CTBR to take into account the crosstalk of the blue to the red channel. In the present example, the transistor _array for implementing the transistor T _{CTBR comprises} 256 individual transistors, wherein, as shown, each individual transistor can be turned on and off by a switch connected in series with it. At the gate of the respective transistor, the voltage generated by the photodiode of the red channel voltage V _{PDR is applied} , wherein the individual transistors whose associated switch is turned on, the voltage V _{PDB is} supplied via its drain terminal, that is, the voltage generated by the blue photodiode. In this way, the weighting factors are digitally configurable.

From the above-mentioned, maximum expected crosstalk of about 10% between the individual channels, an approximate geometry estimate for a configurable transistor array can be derived. The optical output power of each channel is at a resolution of, for example, 8 bits. Thus, the required control accuracy corresponds to 0.2% (= 0.5 LSB) of the maximum modulation of the respective channel. This results in a resolution of 6 bits for the configurable transistor array (corresponds to 64 basic levels of the in 7 shown arrangement) of each channel, wherein the geometries of the respective basic level 0.2% of the sense transistor (T _SG , T _SB and T _SR in 7 ) corresponds.

Claims (14)

Laser module for projection applications, comprising: a drive device ( 14 an input for coupling to a source of payload data to be projected, the payload data to be projected comprising at least a first portion of a first wavelength (R) and a second portion of a second wavelength (G); - at least one first output (E _1R ) for providing a setpoint brightness of the first wavelength (R); and - at least one second output (E _1G ) for providing a setpoint brightness of the second wavelength (G); - At least a first laser diode (LD _R ) for emitting radiation of the first wavelength (R) and at least one second laser diode (LD _G ) for emitting radiation of the second wavelength (G); - At least a first photodiode (PD _R ) having an output for providing an actual value of the brightness, wherein the first photodiode (PD _R ) to the first laser diode (LD _R ) is arranged such that at least a portion of the first laser diode (LD _R ) during operation of the first photodiode (PD _R ) is detectable, and at least one second photodiode (PD _G ) having an output for providing an actual value of the brightness, the second photodiode (PD _G ) to the second laser diode ( LD _G ) is arranged such that at least a portion of the radiation emitted by the second laser diode (LD _G ) during operation is detectable by the second photodiode (PD _G ); At least one of the first wavelength (R) associated first ( 16R ) and a second laser driver device associated with the second wavelength (G) ( 16G ), each laser driver device ( 16R ; 16G ) comprises: - a first input (E _1R ) connected to the associated output of the drive device ( 14 ) - a second input (E _2R ) coupled to the output of the associated photodiode (PD _R ; PD _G ); - An output (A _R ) for providing a drive signal for the associated laser diode (LD _R , LD _G ); An amplification device ( 20R ) having a variable gain factor (V _R ) connected between the first input (E _1R ) and the output (A _R ) of the respective laser driver device ( 16R ; 16G ) is coupled; and - an evaluation device ( 22R ) having a first input (E _22R1 ) for supplying a _reference value of the brightness with the first input (E _1R ) of the laser driver device ( 16R ; 16G ), a second input (E _22R2 ) _adapted to supply an actual value of the brightness with the second input (E _2R ) of the laser driver device ( 16R ; 16G ) and an output (A _22VR ) for setting the amplification _factor (V _R ) of the associated amplification device ( 20R ), wherein the evaluation device ( 22R ), the amplification factor (V _R ) for the associated amplification device ( 20R ), wherein the evaluation device ( 22R ) is further designed to subtract a second evaluation signal from a first evaluation signal when determining the amplification factor (V _R ), wherein the first evaluation signal is the signal at the first input (E _22R1 ) of the evaluation device ( 22R ), wherein the second evaluation signal, the signal at the second input (E _22R2 ) of the evaluation device ( 22R ), characterized in that the evaluation device ( 22R ) of the first laser driver device ( 16R ) for supplying at least one coupling signal (K _GR , K _BR ) to at least the second laser driver device ( 16G ), wherein the evaluation device ( 22R ) of the first laser driver device ( 16R ), the amplification factor (V _R ) for the first amplification device ( 20R ), taking into account furthermore the at least one coupling signal (K _GR , K _BR ). Laser module according to claim 1, characterized in that each laser driver device ( 16R . 16G ) a D / A converter device ( 18R ) connected between the associated output of the drive device ( 14 ) and the associated amplification device ( 20R ) is coupled. Laser module according to claim 2, characterized in that the at least one coupling signal (K _GR ) the signal at the input of the D / A converter device ( 18G ) of the second laser driver device ( 16G ). Laser module according to claim 2, characterized in that the at least one coupling signal (K _GR ) the signal at the output of the D / A converter device ( 18G ) of the second laser driver device ( 16G ). Laser module according to one of claims 3 or 4, characterized in that the evaluation device ( 22R ) of the first laser driver device ( 16R ) is designed to form the first evaluation signal by adding the signal at its second input (E _22R2 ) and the multiplied by a first predetermined coupling factor coupling signal (K _GR ). Laser module according to claim 2, characterized in that the at least one coupling signal, the signal at the second input (E _22G2 ) of the evaluation device ( 22G ) of the second laser driver device ( 16G ). Laser module according to claim 6, characterized in that the evaluation device ( 22R ) of the first laser driver device ( 16R ) is designed to form the second evaluation signal by subtracting the coupling signal (K _GR ) multiplied by a second predetermined coupling factor from the signal at its second input (E _22R2 ). Laser module according to claim 7, characterized in that the evaluation device ( 22R ) comprises a subtraction device. Laser module according to Claim 8, characterized in that the subtraction device comprises at least one current mirror device, wherein the current mirror device comprises at least one first transistor (T _SR ) which is connected to the signal at the second input (E _22R2 ) of the evaluation device ( 22R ) and at least one second transistor (T _CTGR ) connected to the signal at the second input (E _22G2 ) of the evaluation device ( 22G ) of the second laser driver device ( 16G ) is coupled. Laser module according to claim 9, characterized in that the second predeterminable coupling factor by geometry _{parameters of} the at least one first transistor (T _SR ) and the at least one second transistor (T _CTGR ) is fixed. Laser module according to claim 9, characterized in that the first transistor (T _SR ) and / or the second transistor (T _CTGR ) is realized by an adjustable transistor _array . Laser module according to claim 10, characterized in that each transistor array comprises a plurality of individual transistors, wherein each individual transistor is associated with an electronic switch to switch a predetermined number of the plurality of individual transistors for setting the second predetermined coupling factor in parallel. Laser module according to one of the preceding claims, characterized in that the laser module at least two, preferably two or three, laser driver devices ( 16R . 16G . 16B ), wherein each laser driver device ( 16R . 16G . 16B ) for supplying a coupling signal / coupling signals (K _GR , K _BR ) to the at least one further laser driver device ( 16R . 16G . 16B ), each laser driver device ( 16R . 16G . 16B ) in determining the amplification factor (V _R ) for its associated amplification device ( 20R ) the coupling signal / the coupling signals (K _GR , K _BR ) of the at least one further laser driver device ( 16R . 16G . 16B ). Method for operating a laser module for projection applications comprising a drive device ( 14 ) having an input for coupling to a source of payload data to be projected, the payload to be projected comprising at least a first portion of a first wavelength (R) and a second portion of a second wavelength (G); at least one first output (E _1R ) for providing a setpoint of the brightness of the first wavelength (R); and at least a second output (E _1G ) for providing a setpoint brightness of the second wavelength (G); at least one first laser diode (LD _R ) for emitting radiation of the first wavelength (R) and at least one second laser diode (LD _G ) for emitting radiation of the second wavelength (G); at least one first photodiode (PD _R ) having an output for providing an actual value of the brightness, wherein the first photodiode (PD _R ) is arranged to the first laser diode (LD _R ) that at least a portion of the of the first laser diode (LD _R ) emitted radiation during operation of the first photodiode (PD _R ) is detectable, and at least one second photodiode (PD _G ) having an output for providing an actual value of the brightness, wherein the second photodiode (PD _D ) to the second laser diode (LD _G ) is arranged so that at least a portion of the radiation emitted by the second laser diode (LD _G ) during operation of the second photodiode (PD _G ) is detectable; at least one of the first wavelength (R) associated first ( 16R ) and a second laser driver device associated with the second wavelength (G) ( 16G ), each laser driver device ( 16R ; 16G ) comprises: a first input (E _1R ) connected to the associated output (E _1R ; E _1G ) of the drive device ( 14 ), a second input (E _2R ) coupled to the output of the associated photodiode (PD _R ; PD _G ); an output (A _R ) for providing a drive signal to the associated laser diode (LD _R ; LD _G ); an amplification device ( 20R ) having a variable gain factor (V _R ) connected between the first input (E _R1 ) and the output (A _R ) of the respective laser driver device ( 16R ; 16G ) is coupled; and an evaluation device ( 22R ₎ having a first input (E _22R1 ) for supplying a _reference value of the brightness with the first input (E _1R ) of the laser driver device ( 16R ; 16G ), a second input (E _22R2 ) _adapted to supply an actual value of the brightness with the second input (E _2R ) of the laser driver device ( 16R ; 16G ) and an output (A _22R ) for adjusting the amplification factor (V _R ) of the associated amplifying device ( 20R ), wherein the evaluation device ( 22R ), the amplification factor (V _R ) for the associated amplification device ( 20R ), wherein the evaluation device ( 22R ) is further designed to subtract a second evaluation signal from a first evaluation signal when determining the amplification factor (V _R ), wherein the first evaluation signal is the signal at the first input (E _221R ) of the evaluation device ( 20R ), wherein the second evaluation signal, the signal at the second input (E _22R2 ) of the evaluation device ( 22R ); characterized by the following steps: a) supplying at least one coupling signal (K _GR , K _BR ) from at least the second laser driver device ( 16G ) to the evaluation device ( 22R ) of the first laser driver device ( 16R ); and b) determining the amplification factor (V _R ) for the first amplification device ( 20R ), taking into account furthermore the at least one coupling signal (K _GR , K _BR ).

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