Driver circuit and method for operating a light-emitting unit

Abstract

Driver circuit for providing a driver current (139) for operation of a light-emitting unit at a brightness level corresponding to a value of a brightness code (301); wherein the driver circuit (100) comprises: - a digital-to-analog converter (DAC) stage (110) configured to generate an intermediate signal (116) depending on the value of the brightness code (301); - an amplification stage (120) configured to amplify the intermediate signal (116) depending on the value of the brightness code (301) in order to provide the driver current (139); and - a control unit (150) configured to - to determine a digital input value (310) into a DAC of DAC stage (110) based on the value of the brightness code (301); and - to set a gain value (320) of the gain level (120) based on the value of the brightness code (301).

Description

Technical area

[0001] This document relates to a driver circuit for a light-emitting unit, wherein the light-emitting unit typically comprises one or more light-emitting diodes (LEDs). background

[0002] A light-emitting unit, typically comprising one or more LEDs, can be controlled depending on a brightness code, wherein the brightness code indicates the brightness level of the light to be emitted by the light-emitting unit. A driver circuit can be configured to convert the (digital) brightness code into a drive signal (in particular, a drive current) supplied to the light-emitting unit to cause the light-emitting unit to emit light at a brightness level corresponding to the brightness code.

[0003] There may be an exponential relationship between the brightness level (and the corresponding value of the brightness code) and the level of the drive signal required to trigger the light-emitting unit to emit light at a specific brightness level.

[0004] The present document concerns the technical problem of providing a driver circuit for a light-emitting device configured to implement a predetermined (exponential) relationship between brightness codes and driver signals in an efficient and accurate manner.

[0005] US 2009 / 0102397 A1 describes a system for controlling multiple light sources. JP 2019-102297 A describes a backlight device and a display device. CN 107231724 A describes a method and system for regulating luminance and color temperature via a single switch. Summary

[0006] According to one aspect, a driver circuit according to the accompanying main claim (claim 1) is described.

[0007] According to a further aspect, a driver circuit according to independent claim 9 (patent claim 9) is described.

[0008] According to a further aspect, a method according to independent claim 14 (patent claim 14) is described.

[0009] It should be noted that the methods and systems described in this document, including their preferred embodiments, can be used independently or in combination with the other methods and systems disclosed in this document. Furthermore, the features presented in the context of a system are also applicable to a corresponding method. Furthermore, all aspects of the methods and systems described in this document can be combined in any way. In particular, the features of the claims can be combined with one another in any way.

[0010] In this document, the term "couple" or "coupled" refers to elements that are in electrical connection with each other, either directly connected, e.g. via wires, or in some other way. Short description of the characters

[0011] The invention will now be explained by way of example with reference to the accompanying drawings, in which Fig. 1 and Fig. 2 show exemplary driver circuits for a light-emitting unit; Fig. 3 shows exemplary signals on the driver circuit; and Fig. 4 shows a flowchart of an exemplary method for generating the drive signal for driving a light-emitting device. Detailed description

[0012] As stated above, the present document relates to providing an accurate and efficient driving circuit for a light-emitting device. Fig. 1 shows a block diagram of an exemplary driver circuit 100, wherein the driver circuit 100 includes a DAC stage 110 and an amplification stage 120. The DAC stage 110 includes a DAC 111 (digital-to-analog converter) configured to control a current source 112 depending on a brightness code. The current from the current source 112 can be mapped to the output of the DAC stage 110 using a current mirror 113. The DAC stage 110 can be operated between a supply voltage 115 and a reference potential 114, e.g., ground.

[0013] Overall, the DAC stage 110 is configured to provide an intermediate signal 116 (in particular, an intermediate current) at the output of the DAC stage 110, wherein the level of the intermediate signal 116 depends on the digital input value of the DAC 111. The DAC 111 can be configured to convert the digital input value into an analog value and / or (using the current source 112) into a current with a specific level, in particular into the intermediate signal 116. The relationship between the digital input value and the level of the intermediate signal 116 can be linear. Therefore, a linear DAC 111 can be used.

[0014] Furthermore, a control unit 150 of the driver circuit 100 may use a predetermined mapping table that maps a brightness code (indicating the brightness level of the light-emitting device driven by the driver circuit 100) to a digital input value for the DAC 111. As in the context of Fig. 3, the mapping between the brightness codes and the digital input values ​​may be non-linear to provide an accurate approximation to a predetermined desired relationship between the drive signals 139 (in particular the drive current) at the output 129 of the driver circuit 100 and the various brightness codes.

[0015] The amplification stage 120 may be configured to amplify the intermediate signal 116 and thereby provide the drive signal 139 of the drive circuit 100, which may be provided to the light-emitting unit, causing the light-emitting unit to emit light at the brightness level corresponding to a given brightness code.

[0016] The gain stage 120 may include an optional scaling unit for setting the input gain of the gain stage 120. The scaling unit may include resistors 124, 125 and switches 122, 123, as shown in Fig. 1. When switch 122 is closed (and switch 123 is open), the total input resistance at the first input of differential amplifier 121 corresponds to the series arrangement of resistors 124, 125. On the other hand, when switch 123 is closed (and switch 122 is open), the total input resistance at the first input of differential amplifier 121 corresponds to resistor 125.

[0017] The gain stage 120 has a main branch 130 and a set of auxiliary branches 140, where the various auxiliary branches 140 can be individually activated or deactivated to set the overall gain of the gain stage 120. Each stage 130, 140 has a transistor 133, 143 and a resistive element 131, 141. The transistors 133, 143 are controlled by the output of the differential amplifier 121. The midpoint between the transistor 133, 143 and the resistive element 131, 141 of a branch 130, 140 can be fed back to the second input of the differential amplifier 121. The resistive elements 131, 141 are coupled to the reference potential 114.

[0018] The driver current 139 at the output 129 of the amplification stage 120 can be provided via a high-voltage protection transistor 134. The level of the driver current 139 is set by the differential amplifier 121. The level of the driver current 139 can be changed by changing the number of activated auxiliary branches 140. An auxiliary branch 140 can be activated by closing the switches 145, 146 of the auxiliary branch 140. Activating one or more auxiliary branches 140 causes the resistive elements 141 of the one or more auxiliary branches 140 to be arranged in parallel with the resistive element 131 of the main branch 130, thereby reducing the effective resistance value of the output branch 130, 140. Furthermore, the transistors 143 of the one or more auxiliary branches 140 are arranged in parallel with the transistor 133 of the main branch 130.

[0019] The driver current l out 139 can be given by Iout=IinRinRout where lin the intermediate current 116 and where R in the resistance value of resistor 125 (when switch 123 is closed and switch 122 is open) or of the series arrangement of resistors 124, 125 (when switch 123 is open and switch 122 is closed). R out is the effective resistance value of the output branch 130, 140 and depends on which of the auxiliary branches 140 are activated. By reducing R out The gain of the amplification stage 120 can be increased. By appropriately selecting the resistance values ​​of the various resistance elements 141 of the various auxiliary branches 140, an exponential amplification curve can be implemented.

[0020] In a preferred example, the following resistance values ​​are used: • Resistance 124: 7*R (where R is any resistance value); • Resistance 125: 3*R; • Resistance 131: 4 / 5*R; • Resistor 141 (auxiliary stage n=1): 2*R; • Resistor 141 (auxiliary stage n=2): 3 / 2*R; etc. • Resistor 141 (auxiliary stage n=N-1): R / 96; • Resistor 141 (auxiliary stage n=N): R / 128;

[0021] The transistors 133, 143 of the various branches 130, 140 are preferably operated within the same operating point. This can be achieved by adjusting the size (in particular the width) of the various transistors 133, 143 according to the resistance value of the resistive element 131, 141 of the respective branch 130, 140.

[0022] Fig. Figure 3 shows, in the upper diagram, a target relationship 309 between the brightness codes 301 and the level 300 of the driver current 139. The brightness code 301 can assume (integer) values ​​between a minimum value 302 (e.g., 0) and a maximum value 303 (e.g., 2048). The level 300 of the driver current 139 can assume values ​​between a minimum level 304 (e.g., 0 mA) and a maximum level 305 (e.g., 25 mA). The target relationship 309 can be an exponential function.

[0023] The gain stage 120 may be configured to provide a set 329 of different gain values ​​320. The gain values ​​320 increase exponentially with increasing values ​​of the brightness code 301. The entire range of possible values ​​of the brightness code 301 may be divided into sub-ranges 308, e.g., between 15 and 20 different sub-ranges 308. For each sub-range 308, a (exactly one) different gain value 320 may be provided. Therefore, each sub-range 308 may be associated with a specific configuration of the gain stage 120 (i.e., with a specific set of activated auxiliary branches 140).

[0024] The set 329 of gain values ​​320 (provided by the gain stage 120) can be used to approximate the desired relationship 309 (in a relatively coarse manner, e.g., using only N different gain values ​​320, e.g., with N between 5 and 20). The DAC stage 110 can be used to provide an interpolation between two adjacent gain values ​​320 of the set 329 of gain values ​​320, such that the combination of the DAC stage 110 and the gain stage 120 provides a relatively accurate approximation to the desired relationship 309.

[0025] The interpolation can be achieved by using a mapping table 319 that maps the various values ​​of the brightness code 301 to various digital input values ​​310 for the DAC 111. The digital input values ​​310 can assume values ​​between a minimum value 314 and a maximum value 315. For each sub-range 308, a mapping can be provided between the values ​​of the brightness code 301 from the respective sub-range 308 and corresponding digital input values ​​310 from the digital input value range. This mapping is typically non-linear in order to provide accurate interpolation between the various (discrete) gain values ​​320. Furthermore, the mapping is typically different for different sub-ranges 308.The assignment can be determined analytically and / or experimentally so that the deviation of the approximated relationship (achieved by the driver circuit 100) and the desired relationship 309 is reduced, in particular minimized.

[0026] Fig. 2 shows another example of a driver circuit 100. The driver circuit 100 has feedback resistors 231, 241 on the feedback paths to the second input of the differential amplifier 121. The feedback resistors 231, 241 of a branch 130, 140 can have a resistance value that is equal to or proportional to the resistance value of the resistance element 131, 141 of the same branch 130, 140. The feedback resistors 231, 241 can be configured such that the ratio of the resistance value between the feedback resistor 231 and the resistance element 131 (used for the main branch 130) is equal to the ratio of the feedback resistor 241 and the resistance element 141 (used for an auxiliary branch). By using the feedback resistors 231, 241, the performance of the driver circuit 100 can be increased.The feedback resistors 231, 241 can be implemented as on-resistance of the feedback switches 236, 146 on the various feedback paths.

[0027] The Fig. The switches 233, 243, 236 shown in Figure 2 can be used to activate or deactivate the individual branches 130, 140.

[0028] Therefore, a driver circuit 100 is described that can be implemented as a programmable current source. The driver circuit 110 comprises a first block 110 with a linear DAC 111 (digital-to-analog converter). Furthermore, the driver circuit 110 comprises a second block 120 having an exponential gain stage. The gain stage 120 is configured to amplify the intermediate current 116 generated by the DAC 111. It should be noted that, alternatively, the DAC 111 may be exponential and the gain stage within the second block 120 may be linear.

[0029] The gain stage 120 includes a feedback loop that regulates the drive current 139 through the output branch 130, 140 so that it corresponds to and / or is proportional to the input current through the input branch. The gain of the gain stage 120 can be programmed by setting the ratio between the associated current elements of the input branch and the output branch. As a result, the required headroom voltage (i.e., the voltage drop across the current sink) is essentially constant over the entire programmable current range. The headroom voltage typically depends only on the input current set by the DAC 111, and the input current remains within limited limits over the entire range of the output current 139.

[0030] By changing the configuration of the input branch of the gain stage 120, the output current 139 increases accordingly, thereby increasing the required headroom voltage on the output side.

[0031] To increase the gain 320 exponentially, the gain 320 of a setting n+1 must be higher by a certain factor than in setting n. This factor can vary between different subranges 308. For the assignment of the input code to the output current, it can be advantageous if the gain factor is constant between different settings or subranges 308. For example, a periodically repeating gain factor (e.g., the gain factors of every other subrange 308 are identical) can be used.

[0032] There are various options for implementing the unit elements of the current source, e.g., resistors, resistor-mode transistors, and current-mode transistors. The implementation shown here uses resistors whose voltage is controlled via a feedback loop.

[0033] The linearity (DNL) of the entire programmable gain stage (especially the current source) may be degraded by the non-ideal nature of the feedback amplifier 121, the transistors 133, 143 and / or the resistive elements 131, 141. As in Fig. As shown in Figure 2, feedback resistors 231, 241 can be used within the feedback lines. In particular, the feedback lines from the intersection of the current-defining resistor 131, 141 and the terminal of the transistor 233, 243 can have a specific resistance value. This can result in a relatively large mismatch between the driver transistors 133, 143.

[0034] The resistance in the feedback path of each current sink branch 130, 140 can be configured to scale with the drive strength of that branch 130, 140. In other words, the ratio between the feedback path resistors 231, 241 can correspond to the ratio of the branch drive strength ratios. Even if the feedback path resistors 231, 241 do not match well, the mismatch error of the transistors 133, 143 can be significantly suppressed. This can be shown mathematically (since the absolute mismatch error of the transistors 133, 143 is multiplied by the relative mismatch error between the feedback path resistors 231, 241). This allows the overall area of ​​the driver circuit 100 to be reduced and the elements defining the feedback path resistor 231, 241 do not have to be placed within the associated array of transistors 133, 143 or resistors 131, 141.

[0035] For current sink regions where the gain setting is constant, the exponential current can only be interpolated by the linear DAC 111.

[0036] Therefore, a combination of a linear DAC 111 and an exponential programmable gain stage 120 is described. The gain of the gain stage 120 can be programmable via the output drive strength for a constant headroom voltage and / or via the input impedance with varying headroom requirements (e.g., relatively high headroom voltage for relatively high output currents 139).

[0037] Weighted averaging may be provided for the various feedback lines of the programmable gain stage branches 130, 140, thereby relaxing the allocation requirements (in terms of sizes) of the various transistors 133, 143 in the gain stage 120.

[0038] The scaling of the gain level may be exponential, so that when changing from one sub-area 308 to the next sub-area 308, the gain value 320 increases by a certain factor, wherein the factor may be different for different transitions between adjacent sub-areas 308.

[0039] The driver circuit 100 may have the following features • a relatively high accuracy (e.g. 1% accurate); • a relatively low headroom voltage (e.g. 100 mV voltage drop at the current sink); • a relatively large dynamic range (e.g. a factor of 1000); • an exponential transfer function (e.g. I out =I in (1,003) code , where code is the value of the brightness code 301; • a relatively high resolution (e.g. min. current step = I max 10 -6 ); • a relatively high linearity (e.g. DNL=0.5LSB); • a relatively high voltage tolerance (e.g. up to 30V voltage drop at the current sink); and / or • fully linear / continuous time operation (ie no PWM of the current sink).

[0040] Fig. 4 shows a flowchart of an exemplary method 400 for providing a driver current 139 for operating a light-emitting device with a brightness level corresponding to a value of a brightness code 301. The method 400 includes generating 401 an intermediate signal 116 as a function of the value of the brightness code 301 using a (linear) digital-to-analog converter (DAC) stage 110. Furthermore, the method 400 includes amplifying 402 the intermediate signal 116 as a function of the value of the brightness code 301 using an (exponential) amplification stage 120 to provide the driver current 139.

[0041] Therefore, a driver circuit 100 for providing a driver current 139 for operating a light-emitting unit (which may have one or more LEDs) with a brightness level corresponding to a value of a brightness code 301 is described. The driver circuit 100 may be configured to approximate a target relationship 309, in particular an exponential relationship, between the value range of the brightness code 301 (which may, for example, be limited to integers) and the value range of the driver current 139. The target relationship 309 may depend on the light-emitting unit or be defined by it. In particular, the target relationship 309 may indicate (for each possible value from the value range of the brightness code) which level of the driver current 139 is required to cause the light-emitting unit to emit light with a brightness level corresponding to the respective value of the brightness code 301.

[0042] The driver circuit 100 includes a digital-to-analog converter (DAC) stage 110 configured to generate an intermediate signal 116 (in particular, an intermediate current) depending on the value of the brightness code 301. The control unit 150 of the driver circuit 100 may be configured to determine a digital input value 310 for input to the DAC 111 of the DAC stage 110 based on the value of the brightness code 301. The DAC 111 may convert the digital input value 310 into the intermediate signal 116 (e.g., using a controlled current source 112).

[0043] Furthermore, the driver circuit 100 includes an amplification stage 120 configured to amplify the intermediate signal 116 depending on the value of the brightness code 301 to provide the driver current 139. The control unit 150 may be configured to set the amplification value 320 of the amplification stage 120 based on the value of the brightness code 301.

[0044] Therefore, a driver circuit 100 is described that combines the use of a gain stage 120 (for providing a relatively coarse exponential gain) and a DAC stage 110 (for providing a relatively accurate interpolation between the gain values ​​320 of the gain stage 120). By combining these two stages 110, 120, a (exponential) target relationship 309 can be approximated in an efficient and accurate manner.

[0045] As indicated above, DAC stage 110 may include a current source 112 controlled by the output of DAC 111 to provide intermediate signal 116 to DAC 111 in dependence upon digital input value 310. Digital input value 310 to DAC 111 may be determined in dependence upon the value of brightness code 301 (e.g., using a predetermined lookup table 319). This allows interpolation between the relatively coarse gain values ​​320 of gain stage 120 to be achieved in an efficient and accurate manner.

[0046] The amplification stage 120 may include a differential amplifier 121 (e.g., an operational amplifier), and the intermediate signal 116 may be coupled to a first input of the differential amplifier 121. The first input of the differential amplifier 121 may be coupled to the reference potential 114 via one or more (input) resistors 124, 125.

[0047] The amplification stage 120 may include a main amplification branch 130 comprising a main transistor 133 controlled by the output of the differential amplifier 121, and a main resistance element 131 arranged between a first terminal of the main transistor 133 and the reference potential 114. The drive current 139 may be provided at the second terminal of the main transistor 133.

[0048] Furthermore, the amplification stage 120 may have a set of auxiliary amplification branches 140 (e.g., N auxiliary amplification branches 140, where N is equal to 2 or more, or 5 or more, or 10 or more). For example, N may be between 2 and 20. Each auxiliary amplification branch 140 may have an auxiliary transistor 143 controlled by the output of the differential amplifier 121, and an auxiliary resistance element 141 arranged between the first terminal of the auxiliary transistor 143 and the reference potential 114. The N different auxiliary amplification branches 140 may be used to set different gain values ​​320 of the amplification stage 120.

[0049] The gain stage 120 may include a set of switches 145, 146 configured to enable or disable the corresponding set of auxiliary gain branches 140 to adjust the gain value 320 of the gain stage 120. By enabling an auxiliary gain stage 140, the auxiliary resistance element 141 may be arranged in parallel with the main resistance element 131, thereby increasing the gain value 320 of the gain stage 120. By enabling different combinations of zero, one, or more auxiliary gain stages 140, different gain values ​​320 can be provided. By selecting the resistance values ​​of the resistance elements 131, 141, a set 329 of exponentially increasing gain values ​​320 can be provided.

[0050] The main amplification branch 130 may have a feedback path from the first terminal of the main transistor 131 to the second input of the differential amplifier 121. Furthermore, each auxiliary amplification branch 140 of the set of auxiliary amplification branches 140 may have a feedback path from the first terminal of the respective auxiliary transistor 143 to the second input of the differential amplifier 121 (when the respective auxiliary amplification branch 140 is activated).

[0051] The driver circuit 100 may be configured to provide a weighted average of the signal on the feedback path of the main amplification branch 130 and the signals on the feedback paths of the one or more activated auxiliary amplification branches 140 to the second input of the differential amplifier 121. The weights for the different feedback paths may depend on the resistance values ​​of the resistance elements 131, 141 of the different amplification branches 130, 140.

[0052] In particular, the main amplification branch 130 may have a main feedback resistor 231 on the feedback path. Furthermore, each auxiliary amplification branch 140 from the set of auxiliary amplification branches 140 may have an auxiliary feedback resistor 241 on the feedback path. The feedback resistors 231, 241 on the various feedback paths may be implemented as the on-resistance of the respective feedback switches 236, 146 on the various feedback paths. The resistance value of the main resistance element 131 may be equal to the resistance value of the main feedback resistor 231. Alternatively or additionally, for each auxiliary amplification branch 140, the resistance value of the auxiliary resistance element 141 may be equal to the resistance value of the auxiliary feedback resistor 241.

[0053] In particular, the ratio of the resistance of the main resistance element 131 to the resistance of the main feedback resistor 231 may be (substantially) equal to the ratio of the resistance of the auxiliary resistance element 141 to the resistance of the auxiliary feedback resistor 241. In particular, the ratios may differ by 10% or less. This may be the case for some or all of the auxiliary amplification branches 140.

[0054] By providing weights on the various feedback paths, the accuracy of the driver circuit 100 can be increased and / or the size requirements of the various transistors 133, 143 can be relaxed.

[0055] Therefore, the gain stage 120 may be configured to assume a set of different configurations (e.g., N different configurations) to provide a corresponding set of 329 different gain values ​​320. The set of 329 different gain values ​​320 may be associated with a corresponding set of different sub-ranges 308 of the value range of the brightness code 301. In particular, the value range of the brightness code 301 may be divided into a sequence of (N) sub-ranges 308. The gain stage 120 may be configured to provide one (in particular, exactly one) gain value 320 for each sub-range 308. The gain values ​​320 from the set of 329 different gain values ​​320 may increase exponentially for subsequent sub-ranges 308 from the set of sub-ranges 308 (thereby providing a rough approximation to the target relationship 309).

[0056] The control unit 150 may be configured to identify the sub-area 308 from the set of different sub-areas 308 in which the value of the brightness code 301 lies. The gain stage 120 may then be operated in the determined configuration to provide the gain value 320 associated with the identified sub-area 308. For this purpose, one or more auxiliary gain branches 140 may be activated.

[0057] The control unit 150 may be configured to determine the digital input value 310 for the value of the brightness code 301 using a (predetermined) mapping table 319, wherein the mapping table 319 may specify a corresponding digital input value 310 for each value from the value range of the brightness code 301.

[0058] The mapping table 319 may include a set of subtables for the corresponding set of subranges 308 of the value range of the brightness code 301. The subtable for a given subrange 308 may be configured such that the sequence of digital input values ​​310 specified by the subtable for the corresponding sequence of values ​​of the brightness code 301 from the given subrange 308 approximates the desired relationship 309 between the brightness code 301 and the drive current 139 within the given subrange 308 (after the various digital input values ​​310 have been amplified using the gain value 320 for the given subrange 308). The same may apply to all subranges 308, thereby providing an efficient and accurate approximation to the desired relationship 309.

[0059] The mapping table can be implemented as a static lookup table or as a lookup algorithm depending on the desired trade-off between area and time.

[0060] The control unit 150 can be configured to identify the sub-range 308 from the set of different sub-ranges 308 in which the value of the brightness code 301 lies. Furthermore, the control unit 150 can be configured to determine the digital input value 310 for the value of the brightness code 301 from the sub-table to which the identified sub-range 308 corresponds. This allows the intermediate signal 116 to be generated accurately.

[0061] It should be noted that the description and drawings merely illustrate the principles of the proposed methods and systems. Those skilled in the art will be able to implement various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and embodiments set forth in this document are expressly intended to be illustrative only to facilitate the reader's understanding of the principles of the proposed methods and systems. Furthermore, all statements contained herein that provide principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to include equivalents thereof.

Claims

[1] A driver circuit for providing a driver current (139) for operating a light-emitting unit with a brightness level corresponding to a value of a brightness code (301); the driver circuit (100) comprising: - a digital-to-analog converter (DAC) stage (110) configured to generate an intermediate signal (116) depending on the value of the brightness code (301); - an amplification stage (120) configured to amplify the intermediate signal (116) in dependence on the value of the brightness code (301) to provide the drive current (139); and - a control unit (150) configured to - to determine a digital input value (310) to a DAC of the DAC stage (110) based on the value of the brightness code (301); and - to set a gain value (320) of the gain stage (120) based on the value of the brightness code (301). [2] Driver circuit according to claim 1, wherein - the gain stage (120) is configured to assume a set of different configurations to provide a corresponding set (329) of different gain values ​​(320); - the set (329) of different gain values ​​(320) is associated with a corresponding set of different sub-ranges (308) of a value range of the brightness code (301); and - the control unit (150) is configured to - to identify the sub-area (308) from the set of different sub-areas (308) in which the value of the brightness code (301) lies; and - operating the gain stage (120) in the configuration to provide the gain value (320) with which the identified sub-region (308) is associated. [3] Driver circuit according to claim 2, wherein the gain values ​​(320) from the set (329) of different gain values ​​(320) for subsequent sub-regions (308) from the set of sub-regions (308) increase exponentially. [4] Driver circuit according to claim 2, wherein - the control unit (150) is configured to determine the digital input value (310) for the value of the brightness code (301) using an assignment table (319); and - the assignment table (319) specifies a corresponding digital input value (310) for each value from a value range of the brightness code (301). [5] Driver circuit according to claim 4, wherein - the assignment table (319) has a set of sub-tables for a corresponding set of sub-ranges (308) of the value range of the brightness code (301); and - the control unit (150) is configured to - to identify the sub-area (308) from the set of different sub-areas (308) in which the value of the brightness code (301) lies; and - to determine the digital input value (310) for the value of the brightness code (301) from the sub-table to which the identified sub-area (308) corresponds. [6] Driver circuit according to claim 5, wherein the sub-table for a given sub-range (308) is designed such that the sequence of digital input values ​​(310) specified by the sub-table for the corresponding sequence of values ​​of the brightness code (301) from the given sub-range (308) and amplified using the gain value (320) for the given sub-range (308) approximates a desired relationship between the brightness code (301) and the driver current (139) within the given sub-range (308). [7] The driver circuit according to claim 1, wherein the driver circuit (100) is configured to approximate a desired relationship between a value range of the brightness code (301) and a value range of the driver current (139). [8] Driver circuit according to claim 1, wherein - the DAC stage (110) comprises a current source controlled by an output of a DAC to provide the intermediate signal (116) in dependence on a digital input value (310) to the DAC; and - the digital input value (310) into the DAC depends on the value of the brightness code (301). [9] A driver circuit for providing a driver current (139) for operating a light-emitting unit with a brightness level corresponding to a value of a brightness code (301); the driver circuit (100) comprising: - a digital-to-analog converter (DAC) stage (110) configured to generate an intermediate signal (116) depending on the value of the brightness code (301); and - an amplification stage (120) configured to amplify the intermediate signal (116) as a function of the value of the brightness code (301) to provide the drive current (139); wherein - the amplification stage (120) comprises a differential amplifier (121); - the intermediate signal (116) is coupled to a first input of the differential amplifier (121); - the amplification stage (120) has a main amplification branch (130) comprising a main transistor (133) controlled by an output of the differential amplifier (121) and a main resistance element (131) arranged between a first terminal of the main transistor (133) and a reference potential; - the driver current (139) is provided at a second terminal of the main transistor (133); - the amplification stage (120) comprises a set of auxiliary amplification branches (140); - each auxiliary amplification branch (140) comprises an auxiliary transistor (143) controlled by the output of the differential amplifier (121) and an auxiliary resistance element (141) arranged between a first terminal of the auxiliary transistor (143) and the reference potential; and - the gain stage (120) comprises a set of switches configured to activate or deactivate the corresponding set of auxiliary gain branches (140) to adjust the gain value (320) of the gain stage (120). [10] Driver circuit according to claim 9, wherein - the main amplification branch (130) has a feedback path from the first terminal of the main transistor (133) to a second input of the differential amplifier (121); and - each auxiliary amplification branch (140) from the set of auxiliary amplification branches (140) has a feedback path from the first terminal of the respective auxiliary transistor (143) to the second input of the differential amplifier (121) when the respective auxiliary amplification branch (140) is activated. [11] Driver circuit according to claim 10, wherein - the driver circuit (100) is configured to provide a weighted average of a signal on the feedback path of the main amplification branch (130) and of signals on the feedback paths of the one or more activated auxiliary amplification branches (140) to the second input of the differential amplifier (121); and - Weights for the different feedback paths depend on resistance values ​​of the resistance elements of the different amplification branches. [12] Driver circuit according to claim 10, wherein - the main amplification branch (130) has a main feedback resistor (231) on the feedback path; and - each auxiliary amplification branch (140) from the set of auxiliary amplification branches (140) has an auxiliary feedback resistor (241) on the feedback path. [13] Driver circuit according to claim 12, wherein for each auxiliary amplification branch (140), a ratio of a resistance value of the main resistance element (131) to a resistance value of the main feedback resistor (231) is equal to a ratio of a resistance value of the auxiliary resistance element (141) to a resistance value of the auxiliary feedback resistor (241). [14] A method for providing a drive current (139) for operating a light-emitting device with a brightness level corresponding to a value of a brightness code (301); the method comprising: - generating an intermediate signal (116) as a function of the value of the brightness code (301) using a digital-to-analog converter, DAC, stage (110); and - amplifying the intermediate signal (116) as a function of the value of the brightness code (301) using an amplification stage (120) to provide the drive current (139); the method further comprising: - determining a digital input value (310) into a DAC of the DAC stage (110) based on the value of the brightness code (301); and - Setting a gain value (320) of the gain stage (120) based on the value of the brightness code (301).

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