CN113905476A

CN113905476A - Exponential dimming method, mapping circuit, dimming circuit and electronic equipment

Info

Publication number: CN113905476A
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: 2022-01-07
Anticipated expiration: 2041-10-28
Also published as: CN113905476B

Abstract

An exponential dimming method, a mapping circuit, a dimming circuit and an electronic device, the method comprising: providing a luminance code; performing an exponential mapping operation on the brightness 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 exponential dimming method, the polynomial formula comprising the power operation and the addition operation is generated through the exponential mapping operation, the very complex high-order exponential operation can be converted into the simple logic expression, so that the exponential 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 the current precision required by the dimming can be still ensured.

Description

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

Technical Field

The invention relates to the technical field of electronics, in particular to an exponential 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 changing day by day. More and more LED drive chips adopt exponential dimming, and compared with linear dimming, the brightness change of the exponential dimming curve can enable human eyes to obtain more comfortable experience and feeling when the brightness is low.

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 index dimming precision and stability realized by the analog circuit are poor.

Disclosure of Invention

In view of this, 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 luminance code; performing an exponential mapping operation on the brightness 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 dimming code, Imin is the minimum value of the driving current, Imax is the maximum value of the driving current, codemax is the maximum value of the luminance code, and code is the luminance code.

Optionally, the polynomial is a 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 code amount in a direct proportional relationship with the luminance code.

Optionally, the exponent mapping operation includes a logic operation, a multiplication operation, and an addition operation;

the logic operation comprises the steps of realizing the constant in the Chebyshev polynomial and the multiplication operation of the constant and the brightness coding quantity according to the brightness coding; the multiplication operation comprises realizing a power operation in the Chebyshev polynomial formula according to a result of the logical operation; the adding operation includes adding a result of the logical operation and a result of the multiplying 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 index dimming method further includes registering a result of each operation step in the index mapping operation process for use in the operation of the next step.

The application also provides an exponent 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, and the polynomial is a formula which is converted based on an exponential dimming formula and comprises power operation and addition operation; the addition module is connected with the power operation module and is used for adding the output results of the power operation module to realize addition operation in the polynomial and generate the dimming code of the exponential 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 used for realizing power operation in the Chebyshev polynomial formula according to the output result of the logic unit; the addition module is connected to the logic unit and the multiplication unit, and is further configured to add an output result of the logic unit and an output result of the multiplication unit to implement an 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 a Chebyshev polynomial and a first monomial 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 monomials to the multiplication unit according to the counting signals; the multiplication unit is connected with the path selection subunit and used for outputting a second monomial corresponding to the power operation according to the counting signal and the first monomial; the path selection subunit is further configured to obtain the second polynomial 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 counting signal, the second polynomial 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 the second monomials output by the multiplication unit.

An exponential dimming circuit comprising said exponential mapping circuit; the exponential dimming circuit further comprises a digital-to-analog conversion module; the dimming code output by the exponential 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 an exponential dimming curve current.

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

I＝Dac_code*Imin

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

Optionally, the exponential dimming curve current further satisfies a chebyshev polynomial formula of a 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 luminance code, and the h is a maximum value of the (code × lna); and a is (Imax/Imin) ^ (1/codemax), wherein Imax is the maximum value of the driving current, and codemax is the maximum value of the brightness code.

An electronic device comprising said exponential mapping circuit, and/or said exponential dimming circuit.

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

Furthermore, by a multiplier with a higher digit number, exponential 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 cycles, and the operation speed is greatly improved.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

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 exponent mapping circuit according to an embodiment of the invention;

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

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

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

With the above figures, certain embodiments of the invention have been illustrated and described in more detail below. The drawings and the description are not intended to limit the scope of the inventive concept in any way, but rather to illustrate it by those skilled in the art with reference to specific embodiments.

Detailed Description

In general, the 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 of the exponential dimming circuit is conversion of luminance coding from exponential to linear.

In an alternative embodiment, LED index dimming is achieved by a table lookup. Specifically, a predetermined dimming curve is formed by artificially setting a brightness code. For example, in linear dimming, 1 to 2047 represents the driving current of the 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 the table look-up method is used, 1 to 2047 are not mapped into linear 1mA to 2047mA, but an exponential mapping mode is adopted to map 1 to 2047 into a certain calculated value of a ^ x function, so that an approximate exponential dimming curve is artificially created as the DAC identifies that the brightness code of the LED is always linear.

However, the lut method requires more hardware resources for the digital circuit, and particularly when the dimming resolution is more and more demanding, the hardware resources will also increase rapidly, for example, the dimming resolution of 11 bits, 2048 steps are total, and corresponding to the selection of the steps, the implementation circuit needs to construct all lut data by 11 × 2047 registers, which may cause the cost of the chip to be too high.

In an alternative embodiment, LED index dimming is achieved by a segmented line method. The method specifically comprises the following steps: and fitting an exponential curve by utilizing a plurality of line segments to realize exponential dimming. Also for example, when dimming with 11bit resolution, the line segment approximation with y 2047x will generate a large error, but the resulting curve will be more and more approximated to the objective function curve by using 256 line segment approximation.

However, in the segmentation method, the more segments the more approaches to the table lookup method, that is, the segmentation method consumes more hardware resources, and when the segments are fewer, the accuracy of the exponential dimming curve becomes worse, and a more ideal fitting effect cannot be obtained.

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

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

The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The following embodiments and their technical features may 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 exponential dimming method of the embodiment includes the following steps:

step S1, providing luminance coding. The brightness coding code determines the brightness level of the LED, the higher the value of the brightness coding 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 code is set according to the actual situation.

And step S2, performing exponential mapping operation on the brightness codes to generate dimming codes, wherein the exponential mapping operation is converted into corresponding polynomial formulas comprising power operation and addition operation based on the exponential dimming formulas. The polynomial includes exponentiation terms and addition operations that implement the addition of the respective exponentiation terms. In some embodiments, the polynomial comprises a chebyshev polynomial. In alternative embodiments, the polynomial includes other formulas that may implement addition and exponentiation.

Generally, 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 needs to be as large as possible, which is taken as 11 bits as an example. For the exponential dimming formula of 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 ═ I (Imax/Imin) ^ (1/codemax), Imax is the maximum current in the driving current of the LED, code is the luminance code, and codemax is the maximum value of the luminance code.

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

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

the Dac _ code is dimming code, Imin is the minimum value of the driving current, Imax is the maximum value of the driving current, codemax is the maximum value of the brightness code, and code is the brightness code.

Taking an example that Imin is 100uA, Imax is 30.6mA, code is 11bit, and codemax is 2047, the above formula (1) is converted into:

I＝100*1.0028^code (3)

the mathematical principle and implementation of the exponential mapping are described below, taking the polynomial as a chebyshev polynomial as an example:

in the above equation (3), since the LED driving current is a linear DAC current output after being converted by a DAC (digital-to-analog converter), the conversion accuracy of the DAC determines the minimum current value, i.e., Imin, in the LED driving current, and for the DAC, the input digital quantity is multiplied by the conversion accuracy to obtain the corresponding analog quantity. Therefore, the driving current of the LED satisfies the following formula:

I＝Dac_code*Imin＝Imin*n^code (4)

where I is the drive 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, in combination with equations (3) and (4), an exponential dimming equation can be derived:

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

as shown in equation (5), the core of the mapping is 1.0028^ code exponential function.

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

the Chebyshev polynomial formula converted from 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 encoding code. Such as x-6 code, or x-12 code. Fine tuning of b0, b1, b2, b3, b4 and b5 has an effect on the final fit.

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

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.

Obtained from the formula (5), 1.0028^ code ^ a ^ code (a ^ 1.0028)

For the exponential function a ^ code, because

a^code＝e^(code*lna) (8)

From a-1.0028, lna-0.002796 results.

Since code is in {0,2047}, code lna is in {0,5.72}, and the convergence field in equation (7) requires the argument x is in {0,1}, there is:

a^code＝{e^[(code*lna)/6]}^6 (9)

formula (7) is substituted with lna ═ 0.002796 and x ═ lna)/6 ═ 0.000466 ═ code, and then the formula (7) is substituted with

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)

Therefore, the exponential dimming formula is converted into the Chebyshev polynomial formula with preset precision.

In an alternative embodiment, the exponent mapping operation includes a logic operation, a multiplication operation, and an addition operation.

The logical operation includes implementing a constant in a chebyshev polynomial and a multiplication operation of the constant with the luminance code according to the luminance code. Logical operations include shift operations, multiply operations, and operations, or operations, non-operations, exclusive or operations, and the like. For example, the constants in the chebyshev polynomial equation and the multiplication terms with the luminance code are implemented using a simple logic operation circuit or a microcontroller. Specifically, using a combinational logic circuit, specific constants such as 32769, 15.25, and the like are implemented through shift operations, and then multiplication terms of b1 × x, b2 × x, b3 × and b4 × x in formula (6) are implemented through multiplication operations, that is, multiplication calculations of 15.25 × code, 0.06 × code, 0.0078 × code, and 0.0032 × code in formula (10) are implemented.

The multiplication operation includes implementing a power operation in the chebyshev polynomial equation according to a result of the logical operation. Multiplication is implemented, for example, using an adder or a microcontroller. Specifically, b 2x ^2, b3 x ^3, b4 x ^4 equal power operation in formula (6) is realized, namely, (0.06x) ^2, (0.0078x) ^3 and (0.0032x) ^4) equal power operation in formula (10) is realized. The multiplier is a 30-by-30 multiplier, multipliers with other digits can be selected according to implementation conditions, and through a multiplier with a higher digit, exponential mapping with very high precision can be realized, 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 adder or microcontroller is used to implement the addition operation, and (b0+ b1 x + b 2x ^2+ b3 x ^3+ b4 x ^4)/b5 in the formula (6) is implemented.

And step 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 realize exponential dimming. The digital-to-analog converter is used for generating a 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 an exponential adjustment curve current so as to realize the exponential dimming of the LED.

According to the index dimming method, the Chebyshev polynomial formula is generated through the index mapping operation, the Chebyshev polynomial can convert very complicated high-order index operation into a simple logic expression, and therefore index dimming can be achieved through a simpler digital circuit. For example, when the above formula (10) is implemented, only 1 multiplier 30 × 30, 1 counter and appropriate combinational logic are used to output dimming code Dac _ code of 15 bits, the circuit is easy to implement, the hardware resource consumption is low, the circuit area can be greatly reduced, meanwhile, the average error between the current value represented by 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, precision and operation speed of the existing dimming method cannot be considered at the same time is solved.

In an optional 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. 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, b 2x ^2 in formula (6) is calculated when the calculation CNT of the counter is 1, b3 x ^2 in formula (6) is calculated when the calculation CNT of the counter is 2, b4 x ^2 in formula (6) is calculated when the calculation CNT of the counter is 3, and the like. In other alternative embodiments, the controller may be used to generate the count signal in software. The time sequence is controlled by the counting signal, so that the exponential operation of high-order digits is conveniently realized.

In an optional embodiment, the exponential dimming method further includes: the result of each operation step in the operation process of the index mapping is registered to be used for 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, an SRAM (static random access memory), and a DRAM (dynamic random access memory), and the operation may be continued by reading the result when the next operation is performed. For example, the register is used for storing b3 x ^2, b3 x ^3, b4 x ^2, b4 x ^3 and b4 x ^4 output by the multiplication unit, and the register is used for storing (b0+ b1 x + b 2x ^2+ b3 x ^3+ b4 x ^4)/b5 output by the addition module. The power operation is conveniently realized by registering the result of each operation step in the exponential mapping operation process, and the problem location is also conveniently carried out when the operation result has deviation.

The invention also provides an exponential mapping circuit.

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

The exponent mapping circuit of the present embodiment includes an exponentiation module 1 and an addition module 2.

The power operation module 1 is used for realizing power operation in a polynomial according to the brightness coding 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 exponentiation terms and addition operations that implement the addition of the respective exponentiation terms. In some embodiments, the polynomial comprises a chebyshev polynomial. In alternative embodiments, the polynomial includes other formulas that may implement addition and exponentiation. The exponentiation module 1 comprises a hardware circuit multiplier and a microcontroller.

The addition module 2 is connected to the exponentiation module 1, and configured to add output results of the exponentiation module to implement addition in the polynomial, so as to generate the dimming code of the exponential mapping circuit. Specifically, the addition module 2 is configured to add the results of the exponentiation to generate the dimming code Dac _ code of the exponent mapping circuit. The adding module 2 comprises an adder or a microcontroller to realize adding operation.

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

Generally, 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 needs to be as large as possible. The mathematical principle of the specific exponential dimming is described above and will not be described herein.

In order to implement the above equation (6), a logic unit 11 is configured to implement the constant in the chebyshev polynomial and the multiplication operation of the constant and the luminance code according to the luminance code. Specifically, the logic unit 11 includes a combinational logic circuit, and implements a shift operation through a shift register or the like to implement specific constants, such as 32769, 15.25, and the like, and implements a multiplication operation through a multiplier or the like to implement multiplication terms of b0, b1 × x, b2 × x, b3 × and b4 × in formula (6). The logic unit 11 is used to perform the multiplication calculation of 15.25 × code, 0.06 × code, 0.0078 × code, and 0.0032 × code in formula (10). In other alternative embodiments, the logic unit 11 includes a combinational logic circuit, and may also include a sequential logic circuit.

And the multiplication unit 12 is connected with the logic unit 11 and is used for realizing the exponentiation 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 idempotent operations of b 2x ^2, b3 x ^3, and b4 x ^4 in the formula (6). The (0.06x) 2, (0.0078x) 3 and (0.0032x) 4) idempotent operations in equation (10) are implemented using multiplication units. The multiplier unit 12 is a multiplier, which is a 30 × 30 multiplier, and multipliers with other numbers of bits may be selected according to the implementation.

And an adding module 2, connected to the logic unit 11 and the multiplying unit 12, for adding the output result of the logic unit 11 and the result of the multiplying unit 12 to implement an addition operation in the polynomial, and generating the dimming code Dac _ code of the exponential mapping circuit. Specifically, (b0+ b1 x + b 2x 2+ b3 x 3+ b4 x 4)/b5 in the formula (6) is realized by using the addition module 2. The addition block 2 comprises an adder and a controller that can implement an addition function.

The exponential mapping circuit of the embodiment can realize dimming coding only by a few logic units, hardware resources are greatly reduced compared with a lookup table method, the precision is high compared with a piecewise linear method, the hardware resources can also be reduced, the operation period is greatly reduced compared with an iteration method, the operation result can be obtained by a small period 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 index 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 monomial obtained by multiplying the constant by 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 monomials according to the counting signals; the multiplication unit is connected with the path selection subunit and used for outputting a second monomial corresponding to the power operation in the Chebyshev polynomial formula according to the counting signal and the first monomial; the path selection subunit is further configured to obtain the second polynomial 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 counting signal, the second polynomial and the result output by the addition module.

Specifically, the logic subunit includes a combinational logic multiplication circuit 111, the count subunit includes a counter 112, the path selection subunit 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, connected to the multiplication unit, and configured to store the second monomials output by the multiplication unit. Specifically, the cache module includes a register 3. In other alternative embodiments, the caching module may be omitted, and caching is implemented by an external caching module.

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

And 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 monomials to the multiplier circuit 121 according to the count signal; a multiplier circuit 121, connected to the selector circuit 113, for outputting a second polynomial corresponding to the power operation according to the count signal and the first polynomial and outputting the second polynomial to a buffer module, i.e., a register 3; a selector circuit 113, further configured to obtain the second polynomial buffered 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; the multiplier circuit 121 is further configured to output the dimming code Dac _ code according to the count signal and the buffered second polynomial and the result output by the adder 21.

The multiplier circuit 121 can realize exponential mapping with very high precision by using 30-by-30 multipliers, and the current precision is as high as 0.05%. In other alternative embodiments, the multiplier circuit 121 may use a higher number of multipliers to achieve higher dimming accuracy.

The following describes the operation process of the exponential mapping circuit in fig. 3 to realize the exponential dimming, taking the above equation (10) as an example:

1. the luminance code of 11 bits 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 ═ TEMP1, calculates 0.06 × code ═ TEMP, calculates 0.0078 × code ═ TEMP3, calculates 0.0032 × code ═ TEMP4 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 outputted from the counter 112 is equal to 1, the selector circuit 113 outputs TEMP2 to the multiplier circuit 121, the multiplier circuit 121 calculates TEMP 2+ TEMP 2-TEMP 5, (0.06 + code) ^ 2-TEMP 5), and buffers TEMP5 into the register 3 while returning to the input terminal of the selector circuit 113.

4. When the count signal CNT output from the counter 112 is 2, the selector circuit 113 outputs the TEMP3 to the multiplier circuit 121, the multiplier circuit 121 calculates TEMP3 × TEMP3 ═ TEMP6, (0.0078 × code) ^2 ═ TEMP6, and returns the TEMP6 to the input terminal of the selector circuit 113.

5. When the count signal CNT outputted from the counter 112 is equal to 3, the selector circuit 113 outputs TEMP6 to the multiplier circuit 121, the multiplier circuit 121 calculates TEMP6 × TEMP3 is equal to TEMP7,

namely, TEMP3 × TEMP3 × TEMP3 ═ 0.0078 × code ^3 ^ TEMP7, buffers TEMP7 into the register, and returns to the input terminal of selector circuit 113.

6. When the count signal CNT output from the counter 112 is 4, the selector circuit 113 outputs TEMP4 to the multiplier circuit 121, the multiplier circuit 121 calculates TEMP4 × (TEMP 4) ^ TEMP8, (0.0032 ^ code) ^2 ^ TEMP 8), and returns TEMP8 to the input terminal of the selector circuit 113.

7. When the count signal CNT outputted from the counter 112 is equal to 5, the selector circuit 113 outputs TEMP8 to the multiplier circuit 121, the multiplier circuit 121 calculates TEMP8 + TEMP 8-TEMP 9, that is, (0.0032 + code) ^ 4-TEMP 9, and buffers TEMP9 into the register 3 while returning to the input terminal of the selector circuit 113.

8. When the count signal CNT output from the counter 112 is 6, 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 buffer TEMP10 to register 3 and return to the input of selector circuit 113.

9. The counter 112 outputs a count signal CNT of 7, the selector circuit 113 outputs TEMP10 to the multiplier circuit 121, and the multiplier circuit 121 calculates TEMP10 TEMP10 TEMP11 and buffers the TEMP11 into a register, and returns the register to the input terminal of the selector circuit 113.

10. When the count signal CNT output from the counter 112 is equal to 8, the selector circuit 113 outputs TEMP11 to the multiplier circuit 121, and the multiplier circuit 121 calculates TEMP11 × TEMP11 to TEMP12, and returns TEMP12 to the input terminal of the selector circuit 113.

11. When the count signal CNT output from the counter 112 is 9, the selector circuit 113 outputs TEMP12 to the multiplier circuit 121, and the multiplier circuit 121 calculates TEMP12 × TEMP11 to TEMP13, i.e., the dimming code DAC _ COD, and buffers the TEMP13 into the register 3.

Thus, the dimming code Dac _ code value 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 function operation of a ^2047 and other high powers through multiplication operation of 9 periods, greatly reduces the operation period, can obtain a result through operation of 9 periods under the condition of keeping few hardware resources, and improves the operation speed.

The invention also provides an exponential 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 will not be described again here.

The exponential dimming circuit of the present embodiment includes the above-mentioned exponential mapping circuit 4 and digital-to-analog conversion module 5. The exponent mapping circuit 4 includes the above 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 exponential mapping circuit 4 is output to the digital-to-analog conversion module 5; the digital-to-analog conversion module 5 is configured to adjust 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, the I is a driving current, the Dac _ code is a dimming code output by the exponential mapping circuit, and the Imin is a 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.

As can be seen from the above discussion, the exponential dimming formula can be converted into a chebyshev polynomial formula with a predetermined precision: that is to say that the first and second electrodes,

I＝e^((code*lna)/h)^h*Imin

wherein the I is a driving current, the e is an euler number, the code is the luminance code, and the h is a maximum value of the (code × lna); and a is (Imax/Imin) ^ (1/codemax), wherein Imax is the maximum value of the driving current, and codemax is the maximum value of the brightness code. Taking Imin as 100uA, Imax as 30.6mA, code as 11bit, and codemax as 2047, a as 1.0028, lna as 0.002796 are given. Since code is equal to {0,2047}, code lna is equal to {0,5.72}, so h is 5.72, and for convenience of calculation, 5.72 is rounded off to obtain an integer of 6, i.e., h is equal to 6.

The exponential dimming circuit generates the dimming code through the exponential mapping circuit, adjusts the driving current according to the dimming code to output the exponential dimming curve current, and can convert very complex high-order exponential operation into a simple logic expression because the dimming code is realized based on the Chebyshev polynomial, so that the exponential dimming can be realized through a simpler digital circuit, the consumption of hardware resources is low, and the current precision required by the dimming can be ensured while the circuit area is greatly reduced.

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 and linear dimming according to an embodiment of the invention is shown.

In fig. 5, the abscissa is the luminance code, i.e., code is 11 bits, and the ordinate is the LED current in mA (milliampere). 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 the exponential mapping circuit is realized by using 1 30 × 30 multiplier, 1 counter and a proper combinational logic and register, so that the average error between the current value represented by the dac _ code dimming code outputting 15 bits and the theoretical value is only 0.2%.

In summary, the exponential dimming circuit of the present invention only needs one multiplier, one counter and few logic units, and can realize exponential dimming in 9 cycles, hardware resources are greatly reduced compared to a lookup table method, the precision is high compared to a piecewise linear method, the hardware resources can also be reduced, the operation cycle is greatly reduced compared to an iterative method, a result can be obtained by operation in 9 cycles under the condition of keeping few hardware resources, and advantages of low hardware resource consumption, high exponential dimming precision, and high operation speed are achieved while taking into account.

Embodiments of the present invention also provide an electronic device, such as a lamp, a dimming power supply, a driver, and the like, including the above exponential dimming circuit. Through the exponential dimming circuit, the electronic equipment uses fewer logic units, and the exponential dimming with extremely high precision is realized.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all equivalent structures or equivalent flow transformations made by using the contents of the specification and the drawings, such as the mutual combination of technical features between various embodiments, or the direct or indirect application to other related technical fields, are included in the scope of the present invention.

Claims

1. An exponential dimming method, comprising:

providing a luminance code;

performing an exponential mapping operation on the brightness 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.

2. The exponential dimming method of claim 1, wherein the exponential dimming formula is:

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

3. The exponential dimming method of claim 2, wherein the polynomial is a chebyshev polynomial;

the chebyshev polynomial formula is:

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 luminance code amount in a direct proportional relationship with the luminance code.

4. The exponential dimming method of claim 3, wherein the exponential mapping operation comprises a logical operation, a multiplication operation, and an addition operation;

the logic operation comprises the steps of realizing the constant in the Chebyshev polynomial and the multiplication operation of the constant and the brightness coding quantity according to the brightness coding;

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

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

5. The exponential dimming method of any one of claims 1-4, further comprising:

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

6. The exponential dimming method of claim 5, further comprising: the result of each operation step in the operation process of the index mapping is registered to be used for the operation of the next step.

7. An exponent mapping circuit, comprising an exponentiation module and an addition module;

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

the addition module is connected with the power operation module and is used for adding the output results of the power operation module to realize addition operation in the polynomial and generate the dimming code of the exponential mapping circuit.

8. The exponent mapping circuit of claim 7, wherein the exponentiation 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 used for realizing power operation in the Chebyshev polynomial formula according to the output result of the logic unit;

the addition module is connected to the logic unit and the multiplication unit, and is configured to add an output result of the logic unit and an output result of the multiplication unit to implement an addition operation in the polynomial, and generate the dimming code.

9. The exponent mapping circuit of claim 8, wherein the logic unit includes: 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 monomial 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 monomials according to the counting signals;

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

the path selection subunit is further configured to obtain the second polynomial 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 counting signal, the second polynomial and the result output by the addition module.

10. The exponent mapping circuit of claim 9, wherein the logic subunit is a combinational logic circuit.

11. The exponent mapping circuit of claim 9, wherein the exponent mapping circuit further comprises a buffer module;

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

12. An exponential dimming circuit comprising the exponential mapping circuit of any one of claims 7-11;

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

the dimming code output by the exponential 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 an exponential dimming curve current.

13. The exponential dimming circuit of claim 12, wherein the exponential dimming curve current satisfies the following equation:

I＝Dac_code*Imin

14. The exponential dimming circuit of claim 13, wherein the exponential dimming curve current further satisfies a chebyshev polynomial equation of a preset precision:

I＝e^((code*lna)/h)^h*Imin

15. An electronic device comprising an exponential mapping circuit according to any of claims 7-11 and/or an exponential dimming circuit according to any of claims 12-14.