CN113905476B

CN113905476B - Index dimming method, mapping circuit, dimming circuit and electronic equipment

Info

Publication number: CN113905476B
Application number: CN202111261355.2A
Authority: CN
Inventors: 蒋知广; 张忠
Original assignee: Shanghai Awinic Technology Co Ltd
Current assignee: Shanghai Awinic Technology Co Ltd
Priority date: 2021-10-28
Filing date: 2021-10-28
Publication date: 2024-02-02
Anticipated expiration: 2041-10-28
Also published as: CN113905476A

Abstract

An exponential dimming method, a mapping circuit, a dimming circuit and an electronic device, wherein the method comprises the following steps: providing a luma code; performing an exponential mapping operation on the luma code to generate a dimming code, the exponential mapping operation being converted into a corresponding polynomial formula including a power operation and an addition operation based on an exponential dimming formula; and adjusting the driving current according to the dimming code to realize exponential dimming. According to the index dimming method, the polynomial formula comprising the power operation and the addition operation is generated through the index mapping operation, and the very complex high-order index operation can be converted into the simple logic expression, so that the index dimming can be realized through a simpler digital circuit, the circuit is easy to realize, the consumption of hardware resources is low, the circuit area can be greatly reduced, and meanwhile, the current precision required by dimming can be ensured.

Description

Index dimming method, mapping circuit, dimming circuit and electronic equipment

Technical Field

The invention relates to the technical field of electronics, in particular to an index dimming method, a mapping circuit, a dimming circuit and electronic equipment.

Background

With the popularization of LED (light emitting diode) lighting applications, the development of LED driving and dimming technologies is also becoming more and more advanced. More and more LED driving chips adopt exponential dimming, and compared with linear dimming, the brightness change of exponential dimming curves can enable human eyes to obtain more comfortable experience and feel at low brightness.

The existing index dimming method is mostly realized by using an analog circuit, the analog circuit realizes index dimming through a corresponding analog device such as a diode, but the precision and the stability of the index dimming realized by the analog circuit are poor.

Disclosure of Invention

In view of the above, the present invention provides an exponential dimming method, a mapping circuit, a dimming circuit and an electronic device, so as to solve the problem of poor precision and stability caused by dimming using an analog circuit in the prior art.

An exponential dimming method comprising: providing a luma code; performing an exponential mapping operation on the luma code to generate a dimming code, the exponential mapping operation being converted into a corresponding polynomial formula including a power operation and an addition operation based on an exponential dimming formula; and adjusting the driving current according to the dimming code to realize exponential dimming.

Optionally, the exponential dimming formula is:

Dac_code＝((Imax/Imin)^(1/codemax))^code；

wherein, dac _code is a dimming code, imin is a minimum value of driving current, imax is a maximum value of driving current, codemax is a maximum value of brightness code, and code is the brightness code.

Optionally, the polynomial is chebyshev polynomial;

the chebyshev polynomial formula is: dac _code= (b0+b1 x+b2 x 2+b3 x 3+b4 x 4)/b 5; the b0, b1, b2, b3, b4 and b5 are constants, and the x is a luminance coding amount in a proportional relationship with the luminance coding code.

Optionally, the exponent map operation includes a logical operation, a multiplication operation, and an addition operation;

the logic operation comprises the realization of chebyshev polynomial medium constant according to the brightness code and the multiplication operation of the constant and the brightness code quantity; the multiplication operation comprises realizing power operation in the Chebyshev polynomial formula according to the result of the logic operation; the addition operation includes adding a result of the logical operation and a result of the multiplication operation to generate the dimming code.

Optionally, the exponential dimming method further includes: generating a counting signal, and controlling the time sequence of each operation step in the exponential mapping operation process according to the counting signal.

Optionally, the method further includes registering the result of each operation step in the index mapping operation process for the operation of the next step.

The application also provides an exponential mapping circuit, which comprises a power operation module and an addition module; the power operation module is used for realizing power operation in a polynomial according to brightness coding, wherein the polynomial is a formula which is converted based on an exponential dimming formula and comprises power operation and addition operation; and the addition module is connected with the power operation module and is used for adding the output result of the power operation module to realize addition operation in the polynomial and generate the dimming code of the exponent mapping circuit.

Optionally, the power operation module includes: a logic unit and a multiplication unit; the logic unit is used for realizing the constant in the Chebyshev polynomial and the multiplication operation of the constant and the brightness code according to the brightness code; the multiplication unit is connected with the logic unit and is used for realizing the power operation in the Chebyshev polynomial formula according to the output result of the logic unit; the addition module is connected with the logic unit and the multiplication unit and is further used for adding the output result of the logic unit and the output result of the multiplication unit to realize addition operation in the polynomial and generate the dimming code.

Optionally, the logic unit includes: a logic unit, a counting subunit and a path selection subunit; the logic unit is used for outputting a constant in the chebyshev polynomial according to the brightness code and a first single formula after multiplying the constant and the brightness code; the counting subunit is used for generating a counting signal; the path selection subunit is connected with the counting subunit and the logic subunit and is used for outputting the corresponding first single item to the multiplication unit according to the counting signal; the multiplication unit is connected with the passage selection subunit and is used for outputting a second single equation corresponding to the power operation according to the counting signal and the first single equation; the path selection subunit is further configured to obtain the second single form and a result output by the addition module, and output the result to the multiplication unit according to the count signal; the multiplication unit is further configured to output the dimming code according to the count signal, the second single equation, and the result output by the addition module.

Optionally, the logic unit is a combinational logic circuit.

Optionally, the exponent mapping circuit further includes a buffer module; the buffer module is connected with the multiplication unit and used for storing a second single form output by the multiplication unit.

An index dimming circuit comprises the index mapping circuit; the exponential dimming circuit further comprises a digital-to-analog conversion module; the dimming code output by the index mapping circuit is output to the digital-to-analog conversion module; the digital-to-analog conversion module is used for adjusting the driving current according to the dimming code so as to output exponential dimming curve current.

Optionally, the exponential dimming curve current satisfies the following formula:

I＝Dac_code*Imin

wherein, I is driving current, dac _code is dimming code output by the exponential mapping circuit, and Imin is conversion precision of the digital-to-analog conversion module.

Optionally, the exponential dimming curve current further satisfies a chebyshev polynomial formula with preset precision: i=e ((code lna)/h)/(h) Imin

Wherein, the I is a driving current, the e is an euler number, the code is the luma code, and the h is the maximum value of the (code x lna); the a= (Imax/Imin)/(1/codemax), the Imax is the maximum value of the driving current, and the codemax is the maximum value of the brightness code.

An electronic device comprises the index mapping circuit and/or the index dimming circuit.

According to the index dimming method, the mapping circuit, the dimming circuit and the electronic equipment, the Chebyshev polynomial formula is generated through index mapping operation, and the Chebyshev polynomial can convert very complex high-order index operation into a simple logic expression, so that index dimming can be realized through a simpler digital circuit, the circuit is easy to realize, the hardware resource consumption is low, the circuit area can be greatly reduced, and meanwhile, the current precision required by dimming can be still ensured.

Furthermore, by using a multiplier with a higher bit number, index mapping with very high precision can be realized, and the current precision is as high as 0.05%.

Furthermore, compared with iterative operation, the operation result can be obtained only by a few operation periods, and the operation speed is greatly improved.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a flowchart of an exponential dimming method according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of an index mapping circuit according to an embodiment of the invention;

FIG. 3 is a schematic diagram of an exponential mapping circuit according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of an exponential dimming circuit according to an embodiment of the present invention;

fig. 5 is a graph of exponential dimming versus linear dimming according to an embodiment of the present invention.

Specific embodiments of the present invention have been shown by way of the above drawings and will be described in more detail below. The drawings and the written description are not intended to limit the scope of the inventive concepts in any way, but rather to illustrate the inventive concepts to those skilled in the art by reference to the specific embodiments.

Detailed Description

In general, an exponential dimming circuit is composed of an exponential mapping circuit of a digital part and an analog DAC (digital-to-analog converter) circuit, and the core is conversion of luminance coding from exponential to linear.

In an alternative embodiment, LED index dimming is achieved by a look-up table. Specifically, a predetermined dimming curve is formed by artificially setting a luminance code. For example, in linear dimming, 1 to 2047 represents a driving current of an LED of 1mA to 2047mA, and the brightness code of the LED is the resolution of the driving current of the LED, which determines the brightness level of the LED. When using the table look-up method, 1 to 2047 is not mapped to linear 1mA to 2047mA, but 1 to 2047 is mapped to the calculated value of a certain a x function by adopting an exponential mapping mode, thus, the DAC recognizes that the brightness code of the LED is always linear, and an approximate exponential dimming curve is created artificially.

However, the look-up table method requires more hardware resources for the digital circuit, especially when the dimming resolution is required to be higher and higher, for example, the hardware resources are also rapidly increased, for example, dimming with 11bit resolution, and 2048 gears are used in total, and corresponding to these gear selections, the implementation circuit needs 11×2047 registers to construct all the look-up table data, which may make the cost of the chip too high.

In an alternative embodiment, LED index dimming is achieved by a segmented line approach. The method comprises the following steps: and utilizing the multi-segment line segments to fit an exponential curve, and realizing exponential dimming. Also taking dimming with 11bit resolution as an example, the use of a line segment approximation of y=2047x produces a large error, but the resulting curve can be made to approach the objective function curve more and more by using a 256 line segment approximation.

However, in the segmentation method, the more segments are, the more the table look-up method is approached, that is, the segmentation method consumes more hardware resources, and when the segments are fewer, the accuracy of the exponential dimming curve becomes poor, and a more ideal fitting effect cannot be obtained.

In an alternative embodiment, LED index dimming is achieved by an iterative method. The iteration method is to carry out iterative multiplication on the base number for a designated number of times through a multiplication module so as to realize exponential dimming. For example, when x=2, y=a×a can be calculated by the multiplication module, and only one period of multiplication calculation is needed to obtain a result; when x=100, the multiplication module calculates y=a≡100, and then the multiplication of 99 cycles is needed to obtain the result. It can be seen that when the resolution is high, for example, 11 bits (2047), and when the input brightness code is 2047, 2047 iterative multiplications are required, which can make the response time of the chip too long, or require extremely high frequency, and cannot achieve good effects in terms of precision and operation speed.

Based on the above problems, the present invention provides an exponential dimming method.

The following description of the embodiments of the present invention will be made in detail and with reference to the accompanying drawings, wherein it is apparent that the embodiments described are only some, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to fall within the scope of the invention. The various embodiments described below and their technical features can be combined with each other without conflict.

The invention provides an index dimming circuit which realizes LED index dimming through a digital circuit.

Referring to fig. 1, a flowchart of an exponential dimming method according to an embodiment of the invention is shown.

The index dimming method of the present embodiment includes the following steps:

step S1, providing brightness coding. The brightness code determines the brightness level of the LED, and the larger the value of the brightness code is, the finer the dimming is, but the more hardware resources are occupied, and the slower the operation speed is. The value of the specific luminance coding code is set according to the actual situation.

And S2, performing an exponential mapping operation on the brightness code to generate a dimming code, wherein the exponential mapping operation is converted into a corresponding polynomial formula comprising a power operation and an addition operation based on an exponential dimming formula. The polynomial includes a power operation term and an addition operation that performs addition of the respective power operation terms. In some embodiments, the polynomial comprises a chebyshev polynomial. In alternative embodiments, the polynomial includes other formulas that may implement additions and exponentiations.

In general, the exponential dimming formula is determined by the maximum current and the minimum current in the driving current, and if a finer dimming curve is desired, the number of bits (i.e. resolution) of the luminance code should be as large as possible, here, 11 bits are taken as an example. For the exponential dimming formula of the LED, there are

I＝Imin*n^code (1)

Wherein I is the driving current of the LED, imin is the minimum current in the driving current of the LED, n= (Imax/Imin)/(1/codemax), imax is the maximum current in the driving current of the LED, code is the luminance coding, and codemax is the maximum value of the luminance coding code.

As can be derived from the above and formula (1),

Dac_code＝((Imax/Imin)^(1/codemax))^code (2)

wherein, dac _code is a dimming code, imin is a minimum value of driving current, imax is a maximum value of driving current, codemax is a maximum value of brightness code, and code is brightness code.

Taking imin=100ua, imax=30.6ma, code 11bit, code=2047 as an example, the above equation (1) is converted into:

I＝100*1.0028^code (3)

the following takes the polynomial as an example of chebyshev polynomial, and explains the mathematical principle and implementation of the exponential mapping:

with the above formula (3), since the driving current of the LED is a linear DAC current outputted after conversion by a DAC (digital-to-analog converter), the conversion accuracy of the DAC determines the minimum current value, i.e., imin, in the driving current of the LED, and for the DAC, the corresponding analog quantity can be obtained by multiplying the inputted digital quantity by the conversion accuracy. Therefore, the driving current of the LED satisfies the following formula:

I＝Dac_code*Imin＝Imin*n^code (4)

where I is the driving current of the LED, dac _code is the dimming code input to the DAC, and Imin is the conversion accuracy of the DAC.

Since the conversion accuracy of the DAC is a fixed value, i.e., imin is a fixed value.

In combination with the above, the exponential dimming equations can be derived in combination with equations (3) and (4):

Dac_code＝[(Imax/Imin)^(1/codemax))^code＝1.0028^code(5)

as can be seen from equation (5), the core of the mapping is a 1.0028 code exponential function.

The following describes the conversion of the exponential dimming equation (5) into a chebyshev polynomial equation of preset precision:

the chebyshev polynomial formula converted by the exponential dimming formula is as follows:

Dac_code＝(b0+b1*x+b2*x^2+b3*x^3+b4*x^4)/b5 (6)

the b0, b1, b2, b3, b4 and b5 are constants, and the x is in direct proportion to the brightness code. Such as x=6×code, or x=12×code. Trimming b0, b1, b2, b3, b4 and b5 will have an impact on the final fit.

When the preset precision of the chebyshev polynomial is 16-bit precision, the chebyshev polynomial formula of 16-bit precision is:

e^x＝(32769+32727x+16704x^2+4597x^3+2275x^4)/32768(7)

wherein b0= 32769, b1=32727, b2= 16704, b3=4597, b4=2275, b5=32768, and euler number e=2.7.

From equation (5), 1.0028 code=a code (a= 1.0028)

For the exponential function a code, due to

a^code＝e^(code*lna) (8)

From a= 1.0028, lna = 0.002796 is obtained.

Further, since code ε {0,2047}, code lna ε {0,5.72}, and the convergence field in equation (7) requires argument x ε {0,1}, let (code lna)/6 ε {0,1}, then there are:

a^code＝{e^[(code*lna)/6]}^6 (9)

the lna = 0.002796 and x= (code lna)/6=0.000466 code are substituted into the formula (7), and there are

a^x＝{e^[(code*lna)/6]}^6

＝[(32769+15.25*code+(0.06*code)^2+(0.0078*code)^3+(0.0032*code)^4)/32768]^6 (10)

Thereby, the conversion of the exponential dimming formula into a chebyshev polynomial formula with preset precision is realized.

In an alternative embodiment, the exponent map operation includes a logical operation, a multiplication operation, and an addition operation.

The logical operation comprises the implementation of constants in the chebyshev polynomial according to the brightness code and the multiplication operation of the constants and the brightness code. Logical operations include shift operations, multiply operations, AND operations, OR operations, NOT operations, and XOR operations, among others. For example, the constants in the chebyshev polynomial equation and the multiplication terms with the luma code are implemented using simple logic circuits or microcontrollers. Specifically, a combinational logic circuit is used to implement specific constants, such as 32769, 15.25, etc., and then multiplication terms of b1×x, b2×x, b3×x and b4×x in the formula (6) are implemented through multiplication operation, that is, multiplication calculation of 15.25×code, 0.06×code, 0.0078×code and 0.0032×code in the formula (10) is implemented.

The multiplication operation includes implementing a power operation in the chebyshev polynomial equation according to a result of the logical operation. For example, the multiplication is implemented using an adder or a microcontroller. Specifically, the exponentiations of b2×2, b3××3, b4××4 and the like in the formula (6) are implemented, that is, the exponentiations of (0.06 x)/(2), (0.0078 x)/(3) and (0.0032 x)/(4) in the formula (10) are implemented. The multiplier is 30 x 30, other bit multipliers can be selected according to the implementation condition, and the index mapping with very high precision can be realized through the higher bit multiplier, and the current precision is as high as 0.05%.

The addition operation includes adding a result of the logical operation and a result of the multiplication operation to generate the dimming code. For example, the addition is implemented using an adder or a microcontroller, and the (b0+b1 x+b2 x 2+b3 x 3+b4 x 4)/b 5 in the formula (6) is specifically implemented.

And S3, adjusting the driving current according to the dimming code to realize exponential dimming. Specifically, the dimming code is input to a digital-to-analog converter to implement exponential dimming. The digital-to-analog converter is used for generating driving current of the LED, the dimming code Dac _code in the formula (10) is input to the digital-to-analog converter, and the digital-to-analog converter performs exponential adjustment on the driving current according to the dimming code Dac _code to generate exponential adjustment curve current so as to realize exponential dimming of the LED.

According to the index dimming method, the Chebyshev polynomial formula is generated through index mapping operation, and the Chebyshev polynomial can convert very complex high-order index operation into a simple logic expression, so that index dimming can be realized through a simpler digital circuit. For example, when the formula (10) is implemented, only 1 multiplier of 30 x 30 and 1 counter are used to output the 15bit dimming code Dac _code, the circuit is easy to implement, the consumption of hardware resources is less, the circuit area can be greatly reduced, meanwhile, the average error between the current value represented by the dimming code Dac _code and the theoretical value is only 0.2%, the current precision required by dimming is high, the error is small, and the problem that the hardware resource consumption, the precision and the operation speed of the existing dimming method cannot be considered is solved.

In an alternative embodiment, the exponential dimming method further includes: generating a counting signal, and controlling the time sequence of each operation step in the exponential mapping operation process according to the counting signal. Such as for example. A counter is used to generate a count control signal to control the timing of each operation step in the exponential mapping operation. For example, b2 x 2 in the calculation formula (6) when the calculation cnt=1 of the counter, b3 x 2 in the calculation formula (6) when the calculation cnt=2 of the counter, b4 x 2 in the calculation formula (6) when the calculation cnt=3 of the counter, and so on. In other alternative embodiments, the controller may also be used to generate the count signal in software. The time sequence is controlled by the counting signal, so that the exponential operation of the high-order number is conveniently realized.

In an alternative embodiment, the exponential dimming method further includes: the result of each operation step in the exponential mapping operation is registered for use in the operation of the next step. For example, the result of each operation step in the index mapping operation process may be registered by a register, SRAM (static random access memory), DRAM (dynamic random access memory), and the operation may be continued by reading out when the next operation is performed. For example, registers are used to store b3 x 2, b3 x 3, b4 x 2, b4 x 3, b4 x 4, and b0+b1 x+b2 x 2+b3+b4 x 4)/b 5 output by the multiplication unit. The exponentiation operation is conveniently realized through the result of each operation step in the register index mapping operation process, and when the operation result deviates, the problem location is also conveniently carried out.

The invention also provides an index mapping circuit.

Referring to fig. 2, a schematic diagram of an exponential mapping circuit according to an embodiment of the invention is shown.

The exponent mapping circuit of this embodiment includes a power operation module 1 and an addition module 2.

The power operation module 1 is used for realizing power operation in a polynomial according to a brightness code, wherein the polynomial is a formula which is converted based on an exponential dimming formula and comprises power operation and addition operation; the polynomial includes a power operation term and an addition operation that performs addition of the respective power operation terms. In some embodiments, the polynomial comprises a chebyshev polynomial. In alternative embodiments, the polynomial includes other formulas that may implement additions and exponentiations. The power operation module 1 includes a hardware circuit multiplier and a microcontroller.

The addition module 2 is connected with the power operation module 1, and is used for adding the output result of the power operation module to realize addition operation in the polynomial, and generating the dimming code of the exponent mapping circuit. Specifically, the adding module 2 is configured to add the result of the power operation to generate the dimming code Dac _code of the exponent mapping circuit. The summing module 2 comprises an adder or a microcontroller to implement the summing operation.

The power operation module 1 specifically includes: a logic unit 11 and a multiplication unit 12.

In general, the exponential dimming formula is determined by the maximum current and the minimum current in the driving current, and if a finer dimming curve is desired, the number of bits (i.e. resolution) of the luminance coding code needs to be as large as possible. The mathematical principles of specific exponential dimming have been described above and are not repeated here.

In order to realize the above formula (6), the logic unit 11 is configured to implement constants in chebyshev polynomials according to the luma code and multiplication operations of the constants and the luma code. Specifically, the logic unit 11 includes a combinational logic circuit, and performs shift operation through a shift register or the like to implement specific constants, such as 32769, 15.25, and performs multiplication operation through a multiplier or the like to implement multiplication terms of b0, b1 x, b 2x, b3 x, and b4 x in the formula (6). The logical unit 11 is used to implement multiplication calculations of 15.25, 0.06, 0.0078, and 0.0032 codes in equation (10). In other alternative embodiments, logic unit 11 includes combinational logic circuitry, and may also include sequential logic circuitry.

And the multiplication unit 12 is connected with the logic unit 11 and is used for realizing the power operation in the Chebyshev polynomial formula according to the output result of the logic unit 11. Specifically, the multiplication unit 12 is used to implement the exponentiations of b2×2, b3×3, b4×4, etc. in equation (6). The exponentiations of (0.06 x)/(2), (0.0078 x)/(3), and (0.0032 x)/(4) in the equation (10) are implemented using multiplication units. The multiplication unit 12 is a multiplier, which is a multiplier of 30×30, or a multiplier with other bits may be selected according to the implementation.

And the adding module 2 is connected with the logic unit 11 and the multiplying unit 12 and is used for adding the output result of the logic unit 11 and the result of the multiplying unit 12 to realize addition operation in the polynomial and generate a dimming code Dac _code of the exponent mapping circuit. Specifically, the addition module 2 is used to implement (b0+b1 x+b2 x 2+b3 x 3+b4 x 4)/b 5 in the formula (6). The adding module 2 includes an adder and a controller capable of implementing an adding function.

The index mapping circuit of the embodiment can realize dimming coding with only few logic units, compared with a lookup table method, hardware resources are greatly reduced, compared with a piecewise linear method, not only is the precision high, but also the hardware resources can be reduced, compared with an iterative method, the operation period is greatly reduced, the operation result can be obtained through fewer periods under the condition of keeping few hardware resources, and the circuit area and the cost have obvious advantages.

Referring to fig. 3, a schematic diagram of an exponential mapping circuit according to an embodiment of the invention is shown.

In the exponent mapping circuit 4 of this embodiment, the logic unit 11 includes: a logic subunit, a counting subunit, and a path selection subunit; the logic subunit is connected with the counting subunit and is used for outputting a constant in the chebyshev polynomial and a first single formula obtained by multiplying the constant and the brightness code according to the brightness code; the counting subunit is used for generating a counting signal; the path selection subunit is connected with the counting subunit and the logic subunit and is used for outputting the corresponding first single formula according to the counting signal; the multiplication unit is connected with the passage selection subunit and is used for outputting a second single formula corresponding to the power operation in the Chebyshev polynomial formula according to the counting signal and the first single formula; the path selection subunit is further configured to obtain the second single form and a result output by the addition module, and output the result to the multiplication unit according to the count signal; the multiplication unit is further configured to output the dimming code according to the count signal, the second single equation, and the result output by the addition module.

Specifically, the logic sub-unit includes a combinational logic multiplication circuit 111, the counting sub-unit includes a counter 112, the path selection sub-unit includes a selector circuit 113, the multiplication unit includes a multiplier circuit 121, and the addition module includes an adder 21.

The exponent mapping circuit of this embodiment further includes a buffer module, which is connected to the multiplication unit and is configured to store a second single equation output by the multiplication unit. Specifically, the buffer module includes a register 3. In other alternative embodiments, the caching module may be omitted, and the caching is implemented by an external caching module.

The combinational logic multiplication circuit 111 is configured to output a constant in chebyshev polynomial and a first single equation obtained by multiplying the constant with the luma code according to the luma code, specifically, a combinational logic circuit is used to implement shift operation through a shift register to implement specific constants, such as 32769, 15.25, and the like, and then implement multiplication operation through a multiplier.

A counter 112 for generating a count signal.

A selector circuit 113 connected to the combinational logic multiplication circuit 111 and the counter 112, for outputting the corresponding first single item to the multiplier circuit 121 according to the count signal; a multiplier circuit 121 connected to the selector circuit 113, for outputting a second single corresponding to the power operation according to the count signal and the first single, and outputting the second single to a buffer module, i.e., a register 3; a selector circuit 113, configured to obtain the buffered second single form in the register 3 and the result output by the adder 21, and output the result to the multiplier circuit 121 according to the count signal; multiplier circuit 121 is further configured to output the dimming code Dac _code according to the count signal and the buffered second singles and the result output by adder 21.

The multiplier circuit 121 uses a 30 x 30 multiplier to achieve very high precision exponential mapping, with current precision up to 0.05%. In other alternative embodiments, multiplier circuit 121 may use a higher number of multipliers to achieve higher dimming accuracy.

The following describes the operation of the index mapping circuit in fig. 3 to implement the index dimming, taking the above formula (10) as an example:

1. the 11-bit luma code is input to the exponent mapping circuit 4 in fig. 3, and the counter 112 starts counting.

2. The combinational logic multiplication circuit 111 generates constants 32769, 15.25, 0.06, 0.0078, 0.0032, and 32768 using a circuit having a shift function, calculates 15.25×code=temp 1, calculates 0.06×code=temp, calculates 0.0078×code=temp 3, calculates 0.0032×code=temp 4 using a multiplication circuit, and inputs calculation results TEMP1, TEMP2, TEMP3, and TEMP4 to the selector circuit 113 and the adder 21, respectively.

3. When the count signal cnt=1 output by the counter 112, the selector circuit 113 outputs TEMP2 to the multiplier circuit 121, and the multiplier circuit 121 calculates TEMP2×temp 2=temp 5, i.e., (0.06×code) ≡2=temp 5, and buffers TEMP5 to the register 3 while returning to the input terminal of the selector circuit 113.

4. When the count signal cnt=2 outputted from the counter 112, the selector circuit 113 outputs TEMP3 to the multiplier circuit 121, and the multiplier circuit 121 calculates TEMP3×temp 3=temp 6, i.e., (0.0078×code) ≡2=temp 6, and returns TEMP6 to the input terminal of the selector circuit 113.

5. When the count signal cnt=3 output from the counter 112, the selector circuit 113 outputs TEMP6 to the multiplier circuit 121, the multiplier circuit 121 calculates TEMP6 temp3=temp7,

i.e., TEMP3 TEMP 3= (0.0078 code)/(3=temp 7), the TEMP7 is buffered in the register and returned to the input of the selector circuit 113.

6. When the count signal cnt=4 outputted from the counter 112, the selector circuit 113 outputs TEMP4 to the multiplier circuit 121, and the multiplier circuit 121 calculates TEMP4×temp 4=temp 8, i.e., (0.0032×code) ≡2=temp 8, and returns TEMP8 to the input terminal of the selector circuit 113.

7. When the count signal cnt=5 outputted from the counter 112, the selector circuit 113 outputs TEMP8 to the multiplier circuit 121, and the multiplier circuit 121 calculates TEMP8×temp 8=temp 9, i.e., (0.0032×code) ≡4=temp 9, and buffers TEMP9 to the register 3 while returning to the input terminal of the selector circuit 113.

8. When the count signal cnt=6 outputted from the counter 112, the selector circuit 113 outputs 32768, TEMP1, TEMP5, TEMP7, TEMP9 to the multiplier circuit 121, and the multiplier circuit 121 calculates

(32768+TEMP1+TEMP5+TEMP7+TEMP9)/32768＝TEMP10

And buffers TEMP10 into register 3 while returning to the input of selector circuit 113.

9. The counter 112 outputs a count signal cnt=7, the selector circuit 113 outputs TEMP10 to the multiplier circuit 121, and the multiplier circuit 121 calculates TEMP10×temp 10=temp 11, and buffers TEMP11 to the register while returning to the input terminal of the selector circuit 113.

10. When the count signal cnt=8 output by the counter 112, the selector circuit 113 outputs TEMP11 to the multiplier circuit 121, and the multiplier circuit 121 calculates TEMP11×temp 11=temp 12 and returns TEMP12 to the input terminal of the selector circuit 113.

11. When the count signal cnt=9 output by the counter 112, the selector circuit 113 outputs the TEMP12 to the multiplier circuit 121, and the multiplier circuit 121 calculates TEMP12×temp 11=temp 13, i.e. the dimming code dac_cod, and buffers the TEMP13 to the register 3.

Thus, the value of the dimming code Dac _code is obtained, and the dimming code Dac _code is outputted through the register 3.

The exponential mapping circuit of the embodiment can realize dimming coding only in 9 periods, can realize the higher-order power function operation such as a 2047 and the like through multiplication operation of 9 periods, greatly reduces the operation period, can calculate and obtain a result through 9 periods under the condition of keeping few hardware resources, and improves the operation speed.

The invention also provides an index dimming circuit.

Referring to fig. 4, a schematic diagram of an exponential dimming circuit according to an embodiment of the invention is shown.

The same reference numerals are used for the same elements in fig. 4 as in fig. 3, and the elements already described in fig. 3 are not repeated here.

The exponential dimming circuit of the present embodiment includes the exponential mapping circuit 4 and the digital-to-analog conversion module 5. The exponent mapping circuit 4 includes the exponent mapping circuit, and the digital-to-analog conversion module 5 includes a digital-to-analog converter DAC and other circuits capable of implementing digital-to-analog conversion.

The dimming code Dac _code output by the index mapping circuit 4 is output to the digital-to-analog conversion module 5; the digital-to-analog conversion module 5 is used for adjusting the driving current according to the dimming code Dac _code to output an exponential dimming curve current.

The exponential dimming formula satisfies the following formula:

I＝Dac_code*Imin

wherein, I is driving current, dac _code is dimming code output by the exponential mapping circuit, and Imin is conversion precision of the digital-to-analog conversion module. The conversion accuracy of the digital-to-analog conversion module is fixed, so the value of Imin is also fixed. The driving current I is in direct proportion to the dimming code Dac _code.

From the above discussion, the exponential dimming formula can be converted into chebyshev polynomial formula with preset precision: that is to say,

I＝e^((code*lna)/h)^h*Imin

wherein, the I is a driving current, the e is an euler number, the code is the luma code, and the h is the maximum value of the (code x lna); the a= (Imax/Imin)/(1/codemax), the Imax is the maximum value of the driving current, and the codemax is the maximum value of the brightness code. Taking imin=100ua, imax=30.6ma, code 11bit, code max=2047 as an example, a=1.0028, lna= 0.002796. Since code e {0,2047}, code e {0,5.72}, h is 5.72, and for ease of calculation, 5.72 is rounded to an integer of 6, i.e., h=6.

According to the index dimming circuit, the dimming code is generated through the index mapping circuit, the driving current is adjusted according to the dimming code to output the index dimming curve current, and because the dimming code is realized based on the Chebyshev polynomial, very complex high-order index operation can be converted into a simple logic expression, so that index dimming can be realized through a simpler digital circuit, the consumption of hardware resources is less, the circuit area is greatly reduced, and meanwhile, the current precision required by dimming is still ensured.

Therefore, the exponential dimming circuit of the present embodiment can realize exponential dimming based on chebyshev polynomials.

Referring to fig. 5, a graph of exponential dimming versus linear dimming is shown in an embodiment of the present invention.

In fig. 5, the abscissa is brightness code, i.e., code is 11 bits, and the ordinate is LED current in mA. Curve 1 is a linear curve and curve 2 is an exponential dimming curve. Compared with a linear curve, the exponential dimming curve has better dimming precision and stability, and the used hardware resources are smaller. Through simulation, when the brightness code is 11 bits, the exponential dimming circuit of the invention is used, and an exponential mapping circuit is realized by using 1 multiplier of 30 x 30, 1 counter and proper combination logic AND register, so that the average error between the current value represented by the 15bit dac_code dimming code and the theoretical value is only 0.2%.

In summary, the exponential dimming circuit of the invention only needs one multiplier, a counter and few logic units, can realize exponential dimming within 9 periods, has greatly reduced hardware resources compared with the lookup table method, has high precision and reduced hardware resources compared with the piecewise linear method, greatly reduces the operation period compared with the iterative method, can calculate to obtain a result through 9 periods under the condition of keeping extremely few hardware resources, and realizes the advantages of low hardware resource consumption, high exponential dimming precision and high operation speed.

The embodiment of the invention also provides electronic equipment such as a lamp, a dimming power supply, a driver and the like comprising the index dimming circuit. Through the index dimming circuit, the electronic equipment uses fewer logic units, and extremely high-precision index dimming is realized.

The foregoing embodiments of the present invention are not limited to the above embodiments, but are intended to be included within the scope of the present invention as defined by the appended claims and their equivalents.

Claims

1. An exponential dimming method, comprising:

providing a luma code;

performing an exponential mapping operation on the luma code to generate a dimming code, wherein the exponential mapping operation is converted into a corresponding polynomial formula comprising a power operation and an addition operation based on an exponential dimming formula, and the exponential dimming formula is as follows:

Dac_code＝((Imax/Imin)^(1/codemax))^code

wherein, the Dac _code is a dimming code, the Imin is a minimum value of a driving current, the Imax is a maximum value of the driving current, the codemax is a maximum value of the brightness code, and the code is the brightness code; the polynomial is chebyshev polynomial, and the chebyshev polynomial formula is as follows:

Dac_code＝(b0+b1*x+b2*x^2+b3*x^3+b4*x^4)/b5

the b0, b1, b2, b3, b4 and b5 are constants, and the x is a brightness coding amount in a proportional relation with the brightness coding code;

and adjusting the driving current according to the dimming code to realize exponential dimming.

2. The exponential dimming method of claim 1, wherein the exponential mapping operation comprises a logical operation, a multiplication operation, and an addition operation;

the logic operation comprises the realization of chebyshev polynomial medium constant according to the brightness code and the multiplication operation of the constant and the brightness code quantity;

the multiplication operation comprises realizing power operation in the Chebyshev polynomial formula according to the result of the logic operation;

the addition operation includes adding a result of the logical operation and a result of the multiplication operation to generate the dimming code.

3. The exponential dimming method according to any one of claims 1-2, wherein the exponential dimming method further comprises:

generating a counting signal, and controlling the time sequence of each operation step in the exponential mapping operation process according to the counting signal.

4. The exponential dimming method of claim 3, wherein the exponential dimming method further comprises: the result of each operation step in the exponential mapping operation is registered for use in the operation of the next step.

5. An exponential mapping circuit is characterized by comprising a power operation module and an addition module;

the power operation module is used for realizing power operation in a polynomial according to brightness coding, the polynomial is a formula which is converted based on an exponential dimming formula and comprises power operation and addition operation, and the exponential dimming formula is as follows:

Dac_code＝((Imax/Imin)^(1/codemax))^code

Dac_code＝(b0+b1*x+b2*x^2+b3*x^3+b4*x^4)/b5

the b0, b1, b2, b3, b4 and b5 are constants, and the x is a brightness coding amount in a proportional relation with the brightness coding code; the power operation module includes: a logic unit and a multiplication unit; the logic unit is used for realizing the constant in the Chebyshev polynomial and the multiplication operation of the constant and the brightness code according to the brightness code; the multiplication unit is connected with the logic unit and is used for realizing the power operation in the Chebyshev polynomial formula according to the output result of the logic unit;

the addition module is connected with the power operation module and is used for adding the output result of the power operation module to realize addition operation in the polynomial and generate dimming codes of the exponent mapping circuit; the addition module is connected with the logic unit and the multiplication unit and is also used for adding the output result of the logic unit and the output result of the multiplication unit to realize addition operation in the polynomial and generate the dimming code.

6. The exponent mapping circuit of claim 5, wherein the logic unit comprises: a logic subunit, a counting subunit, and a path selection subunit;

the logic subunit is used for outputting a constant in the chebyshev polynomial and a first single formula after multiplying the constant and the brightness code according to the brightness code;

the counting subunit is used for generating a counting signal;

the path selection subunit is connected with the counting subunit and the logic subunit and is used for outputting the corresponding first single formula according to the counting signal;

the multiplication unit is connected with the passage selection subunit and is used for outputting a second single formula corresponding to the power operation in the Chebyshev polynomial formula according to the counting signal and the first single formula;

the path selection subunit is further configured to obtain the second single form and a result output by the addition module, and output the result to the multiplication unit according to the count signal;

the multiplication unit is further configured to output the dimming code according to the count signal, the second single equation, and the result output by the addition module.

7. The exponent mapping circuit of claim 6 wherein the logic subunit is a combinational logic circuit.

8. The exponent mapping circuit of claim 6 wherein the exponent mapping circuit further comprises a buffer module;

the buffer module is connected with the multiplication unit and used for storing a second single form output by the multiplication unit.

9. An exponential dimming circuit, characterized by comprising an exponential mapping circuit as claimed in any one of claims 5-8;

the exponential dimming circuit further comprises a digital-to-analog conversion module;

the dimming code output by the index mapping circuit is output to the digital-to-analog conversion module;

the digital-to-analog conversion module is used for adjusting the driving current according to the dimming code so as to output exponential dimming curve current.

10. The exponential dimming circuit of claim 9, wherein the exponential dimming curve current satisfies the following formula:

I＝Dac_code*Imin

11. The exponential dimming circuit of claim 10, wherein the exponential dimming curve current further satisfies a chebyshev polynomial equation of preset precision:

I＝e^((code*lna)/h)^h*Imin

12. An electronic device comprising the exponential mapping circuit of any one of claims 5-8, and/or the exponential dimming circuit of any one of claims 9-11.