Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K7/00—Modulating pulses with a continuously-variable modulating signal
  • H03K7/08—Duration or width modulation ; Duty cycle modulation
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/20—Controlling the colour of the light
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/32—Pulse-control circuits
  • H05B45/325—Pulse-width modulation [PWM]
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/2007—Display of intermediate tones
  • G09G3/2014—Display of intermediate tones by modulation of the duration of a single pulse during which the logic level remains constant
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
  • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
  • G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]

Definitions

• This application relates to systems and methods for the generation of pulse width modulated signals for lighting or for other purposes.
• Pulse width modulation is a common technique for controlling the "- amount of power that is delivered to a device, such as a motor or a lamp.
• PWM Pulse width modulation
• a device such as a motor or a lamp.
• One of the main benefits of PWM is that it is a technique that allows a digital system to achieve relatively high resolution control over the operation of a particular device.
• PWM is a technique commonly employed in motor control to allow a digital signal to control the speed of a motor.
• PWM takes advantage of the fact that a motor is an inductive element that acts like an integrator. Accordingly, the application to that motor of a pulsed digital signal results in the motor integrating over the square ⁇ wave of the pulsed digital signal.
• pulse width modulation is a technique that allows a digital output signal to effectively achieve control over a device as if the digital output signal could be set to an intermediate voltage level.
• Other techniques include interrupt driven processes in which a microprocessor, such as one having a watchdog timer, receives periodic interrupts at a known rate. Each time through the interrupt loop the processor updates one or more output pins, thus creating a pulse width modulated signal on each output pin.
• the rate at which a signal can be modulated is the clock speed multiplied by the number of cycles in the interrupt routine.
• the number of instructions in the interrupt routine and therefore the number of clock cycles can be quite large.
• the time period for executing the update instructions can be significant, and the PWM signal may have poor resolution, lacking fine grain control over the system.
• Still other techniques exist which are effectively combinations of the first two processes, software loops that contain a variable number of instructions for these techniques.
• the processor uses the hardware timer to generate a periodic interrupt, and then, depending on whether the pulse is to be very short or not, either schedules another interrupt to finish the PWM cycle, or creates the pulse by itself in the first interrupt routine by executing a series of instructions consuming a desired amount of time between two PWM signal updates.
• the difficulty with this method is that for multiple PWM channels it is very difficult to arrange the timer based signal updates such that they do not overlap, and then to accurately change the update times for a new value of PWM signals.
• the present disclosure provides methods and systems to generate multiple channels of pulse width modulated signals for any purpose using software techniques at speeds exceeding those commonly achievable with traditional software synthesis.
• the systems and methods described herein provide, in one aspect, a method for modulating the pulse width of control signals generated on a plurality of separate channels.
• the methods described herein are suitable for execution on a microprocessor or micro controller platform that includes a timer interrupt mechanism which will generate an interrupt in response to a timer counting down a selected time interval or time period.
• the timer is set to count _ down a period of time that is representative of a portion, or sub period, of the PWM cycle. For example, the timer can be selected to count down one fourth the time period of one PWM cycle.
• the timer executes an interrupt that causes the micro controller to enter an interrupt service routine (ISR).
• ISR interrupt service routine
• the ISR can review a set of pre-computed values each of which represents the value for a modulated channel for a specific sub period of the PWM cycle.
• the ISR can then write to the I/O pins that are associated with the different modulated channels to set the level of the respective PWM signal on each of the I/O pins.
• the ISR can then determine for that duty cycle which channel is to be further modulated. For example, for a PWM signal that has been subdivided into four sub periods, the ISR can determine that for the first of these sub period, the ISR is to further modulate the PWM signal on the first channel. Similarly, when the ISR occurs during the second sub period, the ISR can modulate the second channel.
• the ISR can modify the signal level on the I/O pin associated with that channel, and execute a delay loop to consume the desired amount of time to maintain the channel in its toggled state.
• the ISR can execute another I/O write operation to toggle the modulated signal to its previous state.
• the ISR can then advance the sub-bookkeeping value to point to the next sub period, and terminate processing.
• the microprocessor or controller platform can go back to normal operation with the timer still being set to trigger upon the lapse of a time interval associated with a sub period of the PWM cycle.
• the systems and methods described herein provide control systems that allow for the modulation of a lamp that includes a red, green, and blue component.
• Each color component of the lamp can be associated with a particular channel.
• Each channel can be separately modulated to control the amount of red, green, or blue in the composite light generated by the lamp. Accordingly, the systems and methods described herein allow for the modulation of the hue of light generated by a colored lamp.
• Fig. 1 depicts one embodiment of a system for modulating the hue of light generated by a color lamp
• Fig. 2 depicts pictorially one cycle of a PWM signal generated across three separate channels, each channel being associated with one color component of the lamp depicted in Fig. 1;
• Fig. 3 depicts a flow chart diagram of an interrupt service routine suitable for use with the system depicted in Fig. 1 ;
• Fig. 4 depicts two PWM channels modulated by an interrupt service routine as shown in Fig. 3.
• Fig. 1 depicts one system 10 that includes a microcontroller element 12, an amplifier 14, and a colored light 18 that includes three colored lamps depicted as a red lamp 20, green lamp 22 and blue lamp 24.
• the microcontroller 12 couples to the amplifier 14 via three separate channels.
• the amplifier couples to the lamp 18 via three separate channels.
• Each of the three channels can be associated with one PWM signal that modulates the operation of a respective one of the colored lamps 20, 22 and 24.
• Each of the elements depicted in Fig. 1 cooperate to provide a system that can modulate the relative intensities of each of the colored lamps 20, 22 and 24 to control the overall hue of the light generated by the lamp 18.
• the system 10 depicted in Fig. 1 can include a microcontroller 12 that can be a conventional microcontroller such as any of the controllers available commercially including those available from the Microchip Company, including any of the PIC family of microcontrollers including the PICmicro 16CXX/17CXX family of microcontrollers.
• the system 10 can include a microprocessor that can access an external memory device for receiving instructions for operating as a system according to the invention.
• other configurations can be employed for providing a data processing platform capable of implementing the systems and methods described herein.
• the systems and methods described herein provide for low-cost control systems that can be operated on lightweight inexpensive data processing platforms such as one time programmable microcontrollers.
• the microcontroller 12 can include I/O pins, each of which can be employed for carrying a control signal, such as the PWM signals described herein.
• Each I/O pin can provide a channel for one of the colored lamp components 20, 22 and 24.
• the system 10 includes an optional amplifier _ element 14.
• the amplifier element 14 can be a power amplifier that amplifies a digital control signal, such as a TTL logic level signal usually having low power.
• the optional amplifier 14 can act to increase the power level of the signal generated by the microcontroller to provide a signal capable of powering the lamp components 20, 22 and 24.
• the development of such power amplifiers is well-known in the art, and any suitable power amplifier can be practiced with the systems described herein without departing from the scope hereof.
• the amplifier element 14 is optional and that in some embodiments, no power amplifier will be necessary as the power required to activate either of the lamp components can be sufficiently generated by the microcontroller 12, or by another platform capable of generating the PWM signals.
• amplifier 14 is depicted as a separate element, the amplifier 14 could be integrated into the lamp component 18.
• Other suitable modifications to the system 10 for integrating or modifying the system 10 to accommodate the power needs of the devices under control can be practiced herewith without departing from the scope of the invention.
• Figs. 2 and 3 depict pictorially the operation of the system 10. Specifically, Fig. 2 depicts the PWM signals that can be generated on the I/O pins of the microcontroller
• the duty cycles shown in Fig. 2 can be generated, in part, by the action of an interrupt service routine (ISR) that operates, for example, as shown in the flow chart diagram of Fig. 3.
• ISR interrupt service routine
• Fig. 2 shows that a period P can be subdivided into four sub periods, depicted in Fig. 2 as subperiods 1, 2, 3 and 4.
• the exemplary period of Fig. 2 lasts for about 1/5,000 seconds in length, with each subperiod being substantially one fourth of that duration.
• the actual duration of the time period will vary according to the application.
• the systems described herein can be employed to generate systems with variable time periods P.
• the time period for each subperiod can be entered into a watchdog timer within the microcontroller.
• the watchdog timer can trigger an interrupt each time the subperiod lapses so that an interrupt is generated that causes the microcontroller 12 to enter an ISR associated with the timer interrupt.
• ISR is depicted in Fig. 3. Specifically, Fig. 3 shows an ISR process 50 that begins in a step 52_ wherein in response to an interrupt occurring, the microcontroller exits out of its current control program and enters an ISR that is associated with that interrupt and that will be executed until completion.
• ISR 50 depicted in Fig. 4 includes a number of steps including step 52 wherein the ISR writes to a port, typically understood as an I/O port on the microcontroller.
• the ISR chooses a channel or channels wherein these channels are to be further modulated, as will be described in detail below.
• the additional modulation takes place by operation of steps 58 through 62 wherein a write operation takes place to toggle the value of the channel and wherein a delay loop maintains the channel in this toggled state for a predetermined or preselected period of time.
• Fig. 4 depicts the modulation of three PWM channels by a system that includes an ISR process such as the ISR process 50 depicted in Fig. 4.
• the processor of the micro controller can schedule an interrupt of at least N equal sub periods.
• Each sub period can be associated with a global PWM update procedure, and a vernier update procedure.
• the sub periods can be denoted by Pi where the first sub period is one, the second is 2 and so on. This is shown in Fig. 2 by the PWM cycle period 40 that shows the PWM cycle as subdivided into four sub periods. Also depicted in Fig. 2 is that the sub period corresponds to the entry of an ISR. This is depicted in Fig. 2 by the demarcations 44 that correspond to the beginning of each of the sub periods.
• the ISR executes a series of operations that modulates the PWM signals of the channels 32, 34 and 38, each of which corresponds to a respective one of the red, green and blue lamps depicted in Fig. 1.
• the ISR can update all PWM signals by selecting from a set of pre-computed - values corresponding to the specific sub period. This can entail a single array read, followed by a single write to update the multiple I/O pins on which the PWM signals are generated.
• Fig. 2 show that when the ISR entry occurs at the beginning of sub period 2, each PWM channel can be modified as a function of the pre-computed values.
• Fig. 2 shows that upon entry into the ISR at the beginning of sub period 2, the system will toggle the values of channels 32, 34 and 38, such that channels
• the ISR can cause the microcontroller to further modulate the signal on a selected one or ones of the PWM channels.
• this further modulation is shown as the toggling of one of the PWM channels for about one fourth of a sub- period.
• the system in sub period 2 can further modulate the value of the PWM channel 34, such that the value of channel 34 toggles from low to high for about one quarter of the duration of the sub period 2.
• This vernier modulation can reduce or increase the PWM "on” of "off ' time, by changing the state of the signal for a desired portion of the sub period.
• the system can advance a sub period bookkeeping value to point to the next sub period, such as for example sub period 3. This positions the system for entering into the ISR upon the next interrupt and modulating the next PWM channel in the series. Using these methods each PWM channel can change multiple times per
• the methods described herein reduce the amount of processor time employed for controlling the modulation period of the PWM channels. For an example, consider two signals A and B with a resolution of 20 counts programmed to 7 and 14 counts respectively. These signals could be depicted as shown in Fig. 4.
• the process described herein can asynchronously update any or all of the global or vernier values, in any order, without having to synchronize with the ISR, and without stopping the ISR.
• the ISR does not have to change any variables which the main code changes or vice-versa. Thus there is no need for interlocks of any kind.
• This software routine can thus utilize a single timer to generate multiple PWM _ signals, with each signal having the resolution of a single processor cycle.
• Microchip PIC microprocessor for example, this allows three PWM signals to be generated with a resolution of 1024 counts, each corresponding to only a single instruction. This allows a PWM period of 1024 instruction cycles, i.e 4882Hz at a 20 MHZ clock. Furthermore, for counts between 256 and 792 the PWM waveform is a non-uniform 9765Hz signal, with much lower noise power than the processor's own straight PWM generator. Other processors and controllers can yield other PWM cycles and timing. While the invention has been disclosed in connection with the preferred embodiments shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is to be limited only by the following claims.

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• Circuit Arrangement For Electric Light Sources In General (AREA)
• Inverter Devices (AREA)

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Cited By (31)

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• 1999
  • 1999-06-25 AU AU53129/99A patent/AU5312999A/en not_active Abandoned
  • 1999-06-25 CA CA002336184A patent/CA2336184A1/en not_active Abandoned
  • 1999-06-25 EP EP99938706A patent/EP1090459A2/en not_active Withdrawn
  • 1999-06-25 WO PCT/US1999/014555 patent/WO2000001067A2/en not_active Application Discontinuation
  • 1999-06-25 JP JP2000557545A patent/JP2002519989A/ja active Pending

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