HK1114958B - Control apparatus and method with increased resolution for use with modulated light sources - Google Patents

Description

High precision control apparatus and method for use with modulated light sources

Technical Field

The present invention relates to the field of lighting devices, and in particular to a method and device for controlling the amount of light emitted by one or more digitally controlled light sources.

Background

Developments in developing and improving the luminous flux of Light Emitting Diodes (LEDs), such as solid state light emitting diodes and organic light emitting diodes, have made these devices suitable for use in general lighting applications, including, for example, buildings, entertainment and roadway lighting. Therefore, light emitting diodes are becoming increasingly competitive with light sources such as incandescent, fluorescent, and high intensity discharge lamps.

Light emitting diodes have many advantages and are generally chosen for their durability, long life, high efficiency, low voltage requirements, and independent control of the color and intensity of the emitted light. They are an improvement over the sophisticated gas discharge, incandescent and fluorescent lighting systems. Solid state light emitting diodes and improved organic light emitting diodes have the ability to produce the same lighting effects belonging to other lighting technologies and the disadvantages associated therewith can be greatly overcome.

Unlike conventional incandescent light sources, the intensity and color of the light emitted by the LEDs can be independently controlled. If a parameter, such as the temperature of a mandrel that affects the spectral distribution of light emitted by the device, is kept constant, then the total emitted light can be controlled without substantially changing the color effect. The LED emits light only when the current through the device exceeds a certain threshold, and the current can therefore steadily increase to a certain maximum value. Therefore, controlling a steady and continuous light output requires precise control of the dc current through the LED. However, some applications only require controlling the average light output over time. Therefore, it is sufficient to obtain the desired lighting effect by rapidly and repeatedly switching between no light emission and the strongest light emission using, for example, Pulse Width Modulation (PWM) or pulse code modulation.

Although PWM is a useful technique for dimming (dimming) LEDs, it must meet a number of special requirements in order to produce a noticeable lighting effect to be comfortable for a person to feel. The need for perceptually smooth dimming, in particular to compensate for the non-linear luminance response of the human visual system using square law equalization, generally requires control of the light output with 12-14 bit accuracy (resolution), whereas standard mainstream hardware PWM circuits only support 10 bit accuracy. Furthermore, since the intensity is 100% modulated, the PWM frequency must typically be higher than about 300Hz to avoid producing perceptible flicker of the light. In addition, because the LED elements can transmit and store heat at different rates, higher PWM frequencies reduce the stress effects caused by device thermal cycling, and in normal LED packages, the detrimental effects of temperature fluctuations are more than about 10 a for³-10⁴The PWM frequency in Hz is negligible.

The problem of LED brightness control has been addressed in a number of U.S. patents, such as U.S. patent No.3,787,752, which describes intensity control for a light emitting diode display. The invention describes how to use a set of power pulses to effectively control LEDs that do not adapt to weak currents in their lighting characteristics, but to currents close to their optimal operating conditions. However, this document does not describe how to repeatedly and discretely set the duty cycle of the LED current pulses, which is also only defined by the applied display.

U.S. patent No.4,090,189 discloses another brightness control circuit for an LED display. The invention describes a PWM method for controlling LEDs over a relatively wide range of brightness levels, which also extends stable operation into the low brightness region. This disclosure also does not describe how to repeatedly and discretely set the duty cycle of the LED current pulses to control the brightness of the LED with the required accuracy.

U.S. patent No.6,833,691 discloses a system and method for providing digital pulse width modulation. The invention describes a pulse width modulation system for a switched power supply circuit providing a high precision pulse width modulated signal. The system is arranged to receive a control signal comprising an (m + n) -bit binary word and to provide a pulse width modulated signal with a predetermined average duty cycle (duty cycle), wherein the accuracy of the signal is substantially 2^(m+n). The pulse width modulation system comprises a circuit for providing 2^mA timing circuit for timing signals, a high-frequency oscillation circuit and a signal generator. Upon receiving the control signal, the high frequency oscillation circuit is used to provide a modified control signal, wherein the modified control signal comprises a set of up to 2ⁿAn m-bit binary word. The signal generator is arranged to receive the timing signal and the modified control signal and to provide a pulse width modulated signal having a duty cycle wherein on average more than 2ⁿThe duty cycle is approximately equal to the predetermined average duty cycle for each of the timing cycles. The switching power supply circuit uses a pulse width modulation signal to control at least one power conversion device. In particular, the invention uses a complex signal generation circuit with adders, delays, multiplexers, memory and register blocks. In addition, in its preferred embodiment, when assuming that the maximum value of the (m + n) -bit word is 2^m+nAt-1, (m + n) -bit control words are mapped onto the timing of the m-bit PWM duty cycles in an artificial manner.

Accordingly, there is a need for an improved and simplified control apparatus and method for use with digitally controlled light sources that can both suppress noise signals and effectively increase the level of accuracy with which the digitally controlled light sources are controlled.

The background information provided above reveals information that applicants believe may have relevance to the present invention. It is not intended, nor should it be taken, that any of the preceding information constitutes prior art against the present invention.

Disclosure of Invention

It is an object of the invention to provide a control device and method for use with a digitally controlled light source. According to one aspect of the present invention, there is provided an apparatus for controlling a light emitting device, the light emitting device including one or more light emitting elements of one or more colors, each of the one or more light emitting elements being energized with an electric current to generate light, the apparatus comprising: means for regulating current to said one or more light-emitting elements using pulse width modulation or pulse code modulation, each of said pulse width modulation and pulse code modulation having a pulse period; and means for modulating the pulse width of each of said pulse periods to increase the accuracy of control of said one or more light-emitting elements.

According to another aspect of the invention, there is provided an extended pulse width modulation method for use in whole 2^MConverting (N + M) -bit signal into 2N-bit width signal in one pulse period^MA stream of words (steam), the method comprising the steps of: receiving a signal of (N + M) bits; decomposing the (N + M) -bit signal into an N-bit part and an M-bit part; translating the N-bit portion into a binary coded number N; translating the M-bit portion into a binary coded number M; compiling (N +1) into the form of an N-bit binary word and feeding said word into said stream over m pulse periods; and in (2)^M-m) pulse periods, compiling N into the form of a binary word of N bits and feeding said word into said stream; thereby, in the whole 2^MForming 2 of N bit width over one pulse period^MA stream of words.

According to a further aspect of the present invention there is provided an extended pulse width modulation apparatus for use in a full 2^MConverting (N + M) -bit signal into 2N-bit width signal in one pulse period^MA stream of words (steam), the device comprising: means for receiving an (N + M) -bit signal; for mixing the (N + M)) Means for decomposing the signal of bits into an N-bit portion and an M-bit portion; means for translating the N-bit portion into a binary-coded number N; means for translating the M-bit portion into a binary-coded number M; means for compiling (N +1) into the form of an N-bit binary word and feeding said word into said stream over m pulse periods; and for use in (2)^M-m) means for encoding N into the form of a binary word of N bits over a period of pulses and feeding said word into said stream; thereby, in the whole 2^MForming 2 of N bit width over one pulse period^MA stream of words.

Drawings

Fig. 1 shows the relationship between temporal frequency and contrast sensitivity of the human visual system.

Fig. 2 shows a block diagram of a control device for a single or multi-channel lighting fixture according to one embodiment of the present invention.

Fig. 3 shows a block diagram of a lighting arrangement that can be controlled using the control device of the invention.

Fig. 4 shows a block diagram of another lighting arrangement that can be controlled using the control device according to the invention.

Fig. 5 shows a schematic circuit diagram of an embodiment of the invention.

Fig. 6 shows a schematic circuit diagram of another embodiment of the invention.

Fig. 7 shows a schematic circuit diagram of another embodiment of the invention.

Fig. 8 shows a flow chart of the main program of the microcontroller for controlling the light source by PWM according to one embodiment of the present invention.

Figure 9 shows a flow diagram for a subroutine for the main routine shown in figure 8.

Figure 10 shows a flow diagram for another subroutine for the main program shown in figure 8.

Fig. 11 shows a flow chart of the main program of another microcontroller for controlling a light source by PCM according to an embodiment of the present invention.

Figure 12 shows a flow diagram for a subroutine for the main routine shown in figure 11.

Figure 13 shows a flow diagram for another subroutine for the main program shown in figure 11.

Detailed Description

Definition of

The term "light source" is used to define one or more devices capable of emitting radiation in any region or combination of regions of the electromagnetic spectrum, where activation and deactivation of the light source can be digitally controlled. For example, the light source may comprise one or more light emitting elements. The light source may also be constituted by a number of light emitting elements emitting light of one or more different colors, for example the light source may be a collection of red, green and blue light emitting elements.

The term "light-emitting element" is used to define any device that emits radiation in any region or combination of regions of the electromagnetic spectrum (e.g., the visible, infrared, or ultraviolet regions) when activated by a potential difference across the device or by an electrical current through the device. Examples of light-emitting elements include semiconductor-based inorganic and organic materials, polymers, phosphor coated or high flux Light Emitting Diodes (LEDs), or other similar devices as would be readily understood.

The term "about" as used herein refers to a deviation of +/-10% from normal. It is to be understood that such a deviation is always included in any given value provided herein, whether or not it is specifically referred to.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

The present invention provides a method and apparatus, which may be at 2^MThe pulse width is modulated over several pulse periods, where each pulse period may have its own pulse width or corresponding duty cycle. Thus, may be at 2^N+MThe accuracy of the individual states controls the resulting time-averaged or effective pulse width, rather than 2 of the common standard method^NThe accuracy of the individual states. By providing additional accuracy, the lighting arrangement with the lighting elements controlled by the inventive control device may thus produce a perceivable smooth dimming of the emitted light.

For example, an N-bit pulse width controller requires an N-bit control word that provides a measurement for the required pulse width or corresponding duty cycle. The pulse width is usually linearly compiled into the control word, so that when the number compiled into the control word is increased by 1, the pulse width is substantially expanded by the time constant, irrespective of the absolute value of the control word. The pulse width of the N-bit pulse width controller in each pulse period can thus be controlled with N-bit accuracy. For example, a control signal having an (N + M) -bit control word may be used to control how the pulse width in the pulse period timing is modulated. In one embodiment, this modulation may be achieved, for example, by: m pulse period sums (2) of pulse width N +1 can be generated using N-bit binary words N and M-bit binary words M^M-m) pulse periods of pulse width n. However, in the present embodiment, the process n is 2^N-1 may be an exception to the present procedure, since n-2^NA 1 increase by 1 is no longer represented by an N-bit binary number of the standard binary coding scheme. For example, only n-2^N-1 can generate 2 of constant n^MA stream of N-bit binary words (steam). Otherwise, it is required that n is 2 without exception^NIn the case of-1, modulating the pulse width during the pulse period sequence can produce m pulse periods with the smallest duty cycle followed by (2)^M-m) pulse periods with the largest duty cycle, as a result of which the effective time-averaged pulse width can be extended over a large range between a maximum value and a minimum value determined by the number mVary in degrees. Therefore, every 2^MThe average pulse width during one of said pulse periods is equal to the effective time-averaged pulse width, i.e. n + m/2^MThus, this method can control the effective pulse width with the accuracy of (N + M) bits.

A particular advantage of the present invention is that m pulse periods are compared to (2)^M-m) pulse periods with a pulse width modulation duty cycle difference of 1/N. As explained in IESNA Lighting Handbook, Ninth Edition, pp.3-21-3-22, the perception of visual flicker of a light source or light emitting surface depends on both temporal frequency and contrast (contrast). Although the contrast value of the light source of modulated pulse width at 100% modulation was 0.01, the light source of extended modulated pulse width had (100/2)^N) % modulation sum (2)^N100)/100) contrast ratio. Thus, according to fig. 1 (in line with the iesnaighting Handbook, Ninth Edition, fig. 3-34), a light source with a PWM frequency of e.g. 50Hz will show visual flicker, but the same light source with an extended PWM frequency of 800Hz and N-4 will not show visual flicker due to a contrast value of 0.16.

In an alternative embodiment, for example, controlling the effective pulse width may comprise: firstly is (2)^M-m) pulses providing n followed by m pulses providing n +1, or optionally modulating the pulse width of each pulse period minus 1. In these cases, however, n-0 is an exception to the normal procedure. Further, controlling the effective pulse width may include varying the pulse width of each pulse period by more than 1, or controlling the effective pulse width may include randomly varying the pulse width in successive pulse periods.

The method and apparatus of the present invention can select the pulse cycle frequency (pulse cycle frequency) as an independent parameter while modulating the pulse width. The pulse cycle frequency may be selected such that the connected light-emitting elements (e.g., LEDs) may operate effectively without accounting for thermal stress, and/or the modulation frequency may be selected to be sufficiently high to help reduce perceptible light flicker. In one embodiment of the invention, the pulse period frequency is selected to be greater than or equal to about 20 kHz. In another embodiment, the pulse cycle frequency is selected to be about 30 kHz.

Fig. 2 shows a block diagram of an embodiment of the present invention for a single or multi-channel lighting fixture. Interface controller 370 provides functionality for forwarding signals that comprise an (N + M) -bit binary signal having a number N represented by the most significant N bits and a number M represented by the least significant M bits of the (N + M) -bit binary signal. The interface controller 370 controls an extended pulse width modulator 372, which generates a signal containing an N-bit pulse width modulated signal and forwards it to the N-bit single or multi-channel pulse width modulation controller 30. The clock 373 provides a synchronization signal having a predetermined frequency to the extended pulse width modulator 372, where the clock 373 may be a separate part or an integrated part of the extended pulse width modulator 372. In this manner, the pulse width modulator may process or generate dependent or multiple independent signals for a single or multi-channel pulse width modulation controller 374, which may be 2^N+MThe effective precision of the bits controls the multi-channel light emitting elements, such as LEDs.

A single or multi-channel pulse width modulation controller 374 may be connected to the single or multi-color light-emitting element luminaire 376, wherein the multi-color luminaire may comprise, for example, light-emitting elements emitting one or more light selected from the red, green, blue, amber, and white ranges. The light-emitting elements associated with the light-emitting device may be classified according to their desired color effect into multiple color channels, where each color channel may have its own single-channel pulse-width modulation controller or may be operatively connected to a predetermined one of the multiple-channel pulse-width modulation controllers. A single or multi-channel pulse width modulation controller may be connected to a single or multi-color channel light emitting device, which may have a combination of red, green, blue, amber or any other color or otherwise classified light emitting elements, for example.

Fig. 3 is a block diagram illustrating a light emitting device that can be controlled using the method and apparatus of the present invention. The light emitting device 100 includes a number of elements including a power source 110, an energy converter 120, a controller 140, and a light source 130. Each element includes an input for receiving an input signal and an output for providing an output signal, although only selected ones of these elements are shown in fig. 3. Under operating conditions, the power supply 110 requires some form of power at its input and provides power in the form of P at its output. The output of the power supply 110 is connected to the input of the energy converter 120, wherein the energy converter 120 converts the electrical energy P provided at its input into a driving current I provided by the energy converter 120 to its output₁. Such a drive current I_iTo the light source 130 to operate it. The controller 140 is operatively connected to the energy converter 120, wherein the controller 140 provides a drive current control signal I to the energy converter 120_s. The controller 140 includes or is adapted to be connected to the control apparatus of the present invention, thereby enabling the controller 140 to operate at 2^N+MThe accuracy level of the individual states controls the energy converter 120. In addition, for example, the controller 140 may provide a signal I to its (optional) interface input or other input device_dA response is made. For example, I_dMay be a dimming sequence desired by the user.

It will be readily appreciated that the light source 130 may include one or more arrays of many light-emitting elements. For example, the arrays may be red, green and blue LEDs or any other color as would be readily understood, such as white or amber LEDs. The energy converter 120 may comprise one or more current drivers, wherein the current drivers may be used, for example, to supply a drive current to a selected array of light-emitting elements.

In another embodiment, a light emitting device controlled using the method and apparatus of the present invention may further comprise a feedback system as shown in fig. 4. The lighting apparatus 200 includes a power source 110, an energy converter 120, a controller 140, and a light source 130. The light emitting device 200 further comprises any combination of a sensor system 250 and a drive current sensor system 260.

Sensor system 250 may sense any combination of one or more input parameters. These parameters may represent one or more portions of heat Q generated by operation of the light-emitting device or one or more portions of spectral density epsilon (lambda) of light emitted by the light source 130. The sensor system may process input parameters that may represent the temperature of a number of light source elements or the amount and spectral composition of light emitted by the light source, which may be provided in the form of, for example, chromaticity and luminance coordinates. Sensor system 250 may provide any combination of g (q) or h (e (λ)) at one or more outputs operatively connected to respective feedback inputs of controller 140.

The drive current sensor system 260 may also be part of the feedback system of the light emitting device 200. The drive current sensor system 260 may sense the drive current I_sAnd provides a measure of the current amplitude at its output, which can then be transmitted to the controller 140. The controller 140 may control I_sIs provided to an energy converter 120 that calculates one or more sensed input signals, including in addition to any input signal I_dHeat, chromaticity, luminance, and drive current. Signal I_dAny combination of measurements of, for example, a desired drive current for the emitted light, a desired luminance, or a desired chromaticity may be represented. The controller comprises or is adapted to be connected to the control device of the invention, thus enabling the controller to control the energy converter 120 to operate at 2^N+MThe accuracy level of the individual states controls the light source 130.

Fig. 5 schematically shows an electronic circuit 301 of an embodiment of the invention, which is capable of implementing the extended pulse width modulation method. The circuit includes an 11-wire input bus 310 for receiving 11-bit parallel input control signals, a sync signal input line 313, an init signal input line 315, and an 8-bit output bus 319 for providing parallel output control signals to a compatible 8-bit PWM controller (not shown). Such circuitry includes exception handling sub-circuits that include 8-line input NAND gates 320 AND 2-line input AND gates 325. Thus, 8 lines of the 11-line input bus carrying the most significant 8-bit input control signal are connected to the first port 331 of the 8-bit adder 330. The input line 333 of the second port of the 8-bit adder carrying the least significant bit is connected to the output 325 of the 2-wire input AND gate 322, wherein the output 325 of the 2-wire input AND gate 322 also constitutes the output of the exception handling sub-circuit. The remaining 7 lines of the second port are not shown and are set to the arithmetic 0. Depending on the adder, this operation can be done by connecting these lines to an arithmetic high voltage or an arithmetic low voltage. 3 of the 11-wire input buses for carrying the least significant 3-bit input control signals are connected to the 3 control signal input wires 341 of the 3-bit programmable counter 340. The 3-bit programmable counter also has a clk signal input 343 and a reset signal input 345 connected to respective lines of the circuit shown in fig. 5 for receiving respective signals under operating conditions. Upon receiving a predetermined change in the sync signal at clk input 351, divide-by-8 counter 350 increments its count. Upon receiving the init signal or incrementing the count by more than 7, the counter is reset to 0. The out (output) signal output 353 of the divide by 8 counter is connected to the reset signal input 345 of the 3-bit programmable counter. When divide by 8 counter 350 is reset to 0, the output signal output on its out signal line resets 3-bit programmable counter 340 via its reset signal input. After detecting a predetermined state change of the sync signal, the 3-bit programmable counter 340 increments its count value and then compares the count value to a number that is compiled into a 3-bit input control signal. When the count value exceeds the compiled number, its output 347 changes from logic 1 to logic 0, AND then the output of the connected 2-wire input AND gate 322 will be 0.

For the embodiment shown in fig. 5, under operating conditions, the exception handling sub-circuit prevents the extended pulse width modulation circuit from adding the existing maximum binary number that is encoded into the most significant 8-bit input control signal. By outputting the adder of the second portThis is achieved when the least significant bit of the incoming signal is set to 0, i.e. when the most significant 8 bits represent a digital 2⁸-1 (typically 2)^N-1), AND combining the output of the 8-wire input NAND gate with the output of the 3-bit programmable counter.

Those skilled in the art will readily appreciate that the total number of bits, the most significant number of bits, and the least significant number of bits of the input control signal may be different from those indicated above. For example, the circuit may be connected to a 10-bit PWM controller that uses the input control signal having the most significant 10 bits and the least significant predetermined number of bits necessary to achieve the desired effective PWM accuracy.

Furthermore, it will be apparent to those skilled in the art that the extended pulse width modulation circuit may further include input or output signal buffering elements such as latches, registers, and multiplexers. The circuit may also be modified to receive input signals or to provide output signals on systems other than parallel bus systems.

In one embodiment, an incrementer (incrementer) may be used in place of the 8-bit adder in the circuit described above. The incrementer may have one control signal input port (e.g. a single 8-bit input port) and increment by 1 the number represented by the signal applied to the control signal input port after detecting a predetermined state change in the trigger signal applied to the trigger signal port under operating conditions.

Fig. 6 schematically shows an electronic circuit 300 according to another embodiment of the invention, in which the divide-by-8 counter shown in fig. 5 is removed, enabling the extended pulse width modulation method. This embodiment uses fewer elements and may be used, for example, if the abrupt change in state of the input control signal always occurs synchronously when the 3-bit counter is reset to 0, or if the change in state of the input control signal occurs asynchronously and the operation of the 3-bit programmable counter 390 to be momentarily reset is not required. Considering the advantages for general lighting applicationsThe pulse period duration or frequency is selected because the change in state of the input control signal typically occurs over 8 pulse periods (typically 2)^MOne pulse period) rather than on a fractional time scale, there is generally no need for any exception handling of asynchronous state changes. Due to 8 pulse periods (typically 2)^MOne pulse period) start, the circuit 300 may generate an average pulse width duty cycle that does not deviate from the specified duty cycle compiled into an 11-bit (typically (N + M) bits) input control signal by more than the equivalent of a single least significant bit change of the input control signal.

Fig. 7 schematically shows another embodiment of an electronic circuit 400 capable of implementing the extended pulse width modulation method, wherein the exception handling sub-circuit shown in fig. 5 is removed. In this embodiment, the 8-bit adder or incrementer "overflows", i.e., resets its output signal to 0, when all of the most significant 8 bits (typically the most significant N bits) are set to logic high. According to the number M of input control signals compiled to the least significant 3 bits (typically the least significant M bits), the circuit sets all output signals to logic 0 during a predetermined variation of M synchronization signals (pulse periods) and for the following 8-M pulse periods (typically (2)^MM) pulse periods) the output signal is set to logic 1, assuming that for all 8 pulse periods (typically 2)^MOne pulse period) of the input control signal is unchanged. For example, the circuit shown in FIG. 7 may be used when there is no need to eliminate such an overflow condition, or when the most significant 8-bit (typically the most significant N-bits) input control signal never simultaneously assumes its logic high (arithmetic 1) value.

In another embodiment, such an extended PWM controller may be implemented in firmware as shown in fig. 8-10, for example for a Philips LPC2132 microcontroller.

Fig. 8 shows main _ PWM function 500 of the microcontroller according to one embodiment of the invention. The function specifies the function PWM _ timersisr as the PWM periodic timer interrupt service routine, initializes the static variable offset to 0, allocates two blocks of random access memory named DataBank0 and DataBank1, each block including N words of M bits, and marks DataBank0 as active. The function then enters a continuous loop in which an external device (such as a remote interface) is queried to obtain the PWM data. Alternatively, data may also be generated in main _ PWM program 500. When PWM data containing an N + M bit word is obtained, the main _ PWM program calls the UpdatePWMData function.

Figure 9 illustrates the UpdatePWMData function 600 of one embodiment of the invention, where the function first determines which database is active (active) and then selects the inactive (inactive) database and writes any subsequent data to it. Before performing N cycles, a cycle counter i is set to 0, msb is set to the most significant N bits of the N + M signal, and lsb is set to the least significant M bits of the N + M signal, wherein in each cycle, if i is less than lsb, the ith memory cell of the selected database is set to msb +1, otherwise the ith memory cell is set to msb. After completion, the active database is marked as inactive and the inactive database is marked as active before returning to the calling function main _ PWM.

Fig. 10 shows a PWM periodic timer interrupt service routine PWM _ timersisr 700 according to one embodiment of the present invention, where the routine first determines which database is active and then selects the active database and reads the data from it. The second offset symbol of the activation database is then read, the PWM period timer hardware register is set to this value, and the static variable offset is incremented. If offset is equal to N, it is reset to 0. The timer interrupt tag is then cleared and the interrupt function PWM _ timersisr is exited.

In one embodiment, the present invention may be applied to Pulse Code Modulation (PCM) instead of PWM. Referring specifically to fig. 2, the PWM controller 374 may be replaced by a PCM controller. The PCM based embodiment may be implemented using a firmware controlled general purpose microcontroller, such as the Philips LPC2132 microcontroller. Fig. 11-13 illustrate this implementation by way of example.

Fig. 11 shows the microcontroller main _ PCM function 800 according to an embodiment of the invention. The function specifies the function PCM _ timersisr as a periodic timer interrupt service routine, initializes the static variables Count and Offset to 0, Mask to 1 and timer Delay to T (where T is typically 1 microsecond), allocates two blocks of random access memory named DataBank0 and DataBank1, where each block includes N words of M bits, and marks DataBank0 as active. The function then enters a continuous loop in which an external device (such as a remote interface) is queried to obtain the PCM data. Alternatively, the data may be generated in a main _1 function (not shown). When obtaining PCM data containing N + M bit words, the main _1 function calls the UpdatePCMData function.

Figure 12 illustrates the UpdatePCMData routing function 900 of one embodiment of the present invention, where the routing function first determines which database is active and then selects the inactive database and writes any subsequent data to it. Before performing N cycles, setting a cycle counter i to O, setting msb to the most significant N bits of the N + M signal, and setting lsb to the least significant M bits of the N + M signal, wherein in each cycle, if i is less than lsb, the ith memory cell of the selected database is set to msb +1, otherwise the ith memory cell is set to msb. After completion, the active database is marked as inactive and the inactive database is marked as active before returning to the calling function main _ 1.

FIG. 13 shows a periodic timer interrupt service routine PCM _ TimeISR 1000 in accordance with one embodiment of the present invention, where the routine determines which database is active and then selects the active database and reads the data from it. The second offset symbol of the activation database is then read AND logically anded with the static mask variable to determine the second count bit of the symbol. If the bit is 0, the LED channel is deactivated; otherwise, the LED channel is activated. If count is less than M, the static variable count is incremented, the static variable mask is multiplied by 2 to effect a logical left shift of the binary bit, and then the static variable delay, which represents the timer delay, is multiplied by 2. Otherwise, count is reset to 0, mask is reset to 1, delay is reset to T, and the static variable offset is incremented. When offset is equal to N, it is reset to 0. Finally, the timer interrupt tag is cleared and the interrupt function PCM _ TimerISR is exited.

In one embodiment of the invention, the pulse width may be defined in terms of control coordinates (N, M, N, M). It will be apparent to those skilled in the art that all of these pulse widths can be transformed into the time domain by applying only a simple coordinate transformation. For example, the duration of the pulse width pw whose duration is specified by the specified PWM control number n may be, for example, (2 ═ pw ═ p^N-1)^-1Xn × PW, where PW is the period of the pulse period. Alternatively, the transformation may be represented by 2^-NX (n × PW) definition; the specific choice is simply a matter of choosing the 0 origin for n.

In one embodiment of the invention, this control method may be performed in a device or system having one or more output channels, whereby each channel is controlled jointly or separately, either simultaneously or in a time-separated multi-channel transmission. For example, each channel may be used to drive a certain color of the light emitting element.

The invention will now be described in connection with specific embodiments. It should be understood that the following examples are intended to describe embodiments of the invention, and are not intended to limit the invention in any way.

Examples

It is known that pulse width modulation of a light emitting element (e.g., an LED) of a solid state light device must have a PWM frequency of at least about 300Hz to avoid perception of visual flicker, a PWM duty cycle accuracy of at least 12 bits, and a PWM frequency of preferably at least about 10kHz to mitigate the deleterious effects of thermal stress on the LED die. The following examples illustrate the control and operation of solid state light emitting devices using the present invention. It will be readily appreciated that for example a plurality of phosphor coated white LEDs may be controlled by one controller, and for example a plurality of red, green, blue and optionally amber LEDs, or white, green and blue LEDs may be controlled by a plurality of controllers, preferably one controller for each LED color.

Example 1: solid state lighting device with extended pulse code modulation control

According to one embodiment of the present invention, a solid state lighting luminaire may be configured as shown in fig. 4, wherein the extended pulse code modulation described above is performed in firmware of a controller 140 (e.g., a commercially available microcontroller) using the extended pulse code modulation method shown in fig. 11-13. One or more corrections are performed on the controller using the collected data reflecting one or more of chromaticity, luminous flux, LED temperature and drive current, thereby effecting feedback control of the solid state light emitting device.

Example 2: solid state lighting device with extended pulse width modulation control

According to one embodiment of the present invention, a solid state lighting luminaire may be configured as shown in fig. 4, wherein the extended pulse width modulation described above may be performed in firmware of a controller 140 (e.g., a commercially available microcontroller) using the extended pulse width modulation method shown in fig. 8-10. The controller may include one or more integrated 10-bit analog-to-digital conversion modules, which may also perform other functions, such as sensor monitoring and feedback control.

Example 3: solid state lighting device with extended pulse code modulation control

Referring to fig. 4, the extended pulse width modulation method disclosed herein may be performed in the controller 140 using the extended pulse width modulation disclosed in fig. 11-13, which is performed in firmware using, for example, a Field Programmable Gate Array (FPGA) preferably with a microcontroller core. Other functions may be performed within the lighting device including, for example, sensor monitoring and feedback control.

It is obvious that the foregoing embodiments of the invention are exemplary and can be varied in many ways. Such present or future variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims (5)

1. An apparatus for controlling a light emitting device, the light emitting device comprising one or more light emitting elements of one or more colors, each of the one or more light emitting elements energized with an electrical current to produce light, the apparatus comprising:

a) a means for regulating current to the one or more light-emitting elements using pulse width modulation or pulse code modulation, each of the pulse width modulation and pulse code modulation having a pulse period;

b) for each pulse periodIs modulated to control the accuracy of the control of the one or more light-emitting elements from 2^NThe control precision of each state is increased to 2^N+MMeans for controlling the precision of states, where N and M are integers greater than zero, said means for modulating the pulse width of each pulse period comprising an N-bit controller; and

wherein the means for modulating the pulse width of each pulse cycle comprises an N-bit adder or incrementer operatively connected to the N-bit controller, the N-bit adder or incrementer providing control signals to the N-bit controller to control the current to the one or more light-emitting elements, the means for modulating the pulse width of each pulse cycle further comprising an M-bit programmable counter connected to the N-bit adder or incrementer, whereby the means for modulating the pulse width of each pulse cycle can provide 2^N+MControl accuracy of individual states.

2. The apparatus of claim 1, wherein the pulse width modulation device further comprises an exception handling circuit operatively connected to the M-bit programmable counter and an N-bit adder or incrementer.

3. The apparatus of claim 2, wherein said pulse width cavity modulation device further comprises a divide-by-N counter operatively connected to said M-bit programmable counter, said divide-by-N counter for resetting said M-bit programmable counter.

4. The apparatus of claim 1, wherein the apparatus operates at a periodic frequency greater than or equal to 20 kHz.

5. The apparatus of claim 4, wherein the apparatus operates at a periodic frequency of 30 kHz.