Control apparatus and method for use with digitally controlled light sources

• US 7,738,002 B2
• Filed: 10/12/2005
• Issued: 06/15/2010
• Est. Priority Date: 10/12/2004
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Robinson, Shane P., Ashdown, Ian
• Primary Examiner(s): Awad; Amr
• Assistant Examiner(s): Sherman; Stephen G
• Application Number:
  US10/557,817
• Publication Number:
  US 20070153026A1
• Time in Patent Office: 1,707 Days
• Field of Search: 345690-692, 345/82, 345/76, 345/204
• US Class Current: 345/691
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2330/028 Generation of voltages supplied to electrode drivers in a matrix display other than LCD
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: H03K 7/08 Duration or width modulation ; Duty cycle modulation
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 52/0229 where the received signal is a wanted signal
• CPC Class Codes: H04W 64/006 with additional information processing, e.g. for direction or speed determination
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

The present invention provides an extension to a standard N-bit digital pulse width control method which can discriminate 2^N discrete pulse widths per pulse cycle. The present invention provides a method and apparatus that can modulate the pulse widths over a period of 2^M pulse cycles in which each pulse cycle can have its own pulse width or respective duty cycle. The resulting time averaged or effective pulse width therefore can be controlled with a resolution of 2^N+M states rather than a resolution of 2^N states as is common with standard methods.

Claims

1. An apparatus for control of a luminaire including one or more light-emitting elements in one or more colors, each of the one or more light-emitting elements being supplied with electrical current to produce light, said apparatus comprising a modulator configured to:

adjust the electrical current to the one or more light-emitting elements using pulse width modulation or pulse code modulation based on an N+M input control signal that includes an N-bit word of N most significant bits having a value n with a maximum value of 2^N−

1, and an M-bit word of M least significant bits having a value m, each of said pulse width modulation and pulse code modulation having a pulse cycle; and

modulate a pulse width for each pulse cycle based on the N+M input control signal for increasing control resolution of the one or more light-emitting elements from 2^N to 2^N+m states when n<

2^N−

1 and n>

0, where N and M are integers greater that zero and N is greater than M, the modulator including an N-bit controller.

2. The apparatus according to claim 1, wherein said modulator for modulating the pulse width comprises a N-bit adder operatively coupled to the N-bit controller, said N-bit adder providing the N-bit controller with N-bit control signals for controlling the electrical current to the one or more light-emitting elements, the modulator further comprising an M-bit programmable counter coupled to the N-bit adder, said M-bit programmable counter being configured to extent the control resolution to the 2^N+M states when the value n the N-bit word is greater than zero and less than the maximum value.

3. The apparatus according to claim 2, wherein said modulator for modulating the pulse width further comprises an exception handling circuit operatively connected to the M-bit programmable counter and the N-bit adder.

4. The apparatus according to claim 3, wherein said modulator for modulating the pulse width further comprises a divide by N counter operatively connected to the M-bit programmable counter, said divide by N counter for resetting the M-bit programmable counter.

5. The apparatus according to claim 1, wherein said modulator for modulating the pulse width comprises an incrementer operatively coupled to the N-bit controller, said incrementer providing the N-bit controller with control signals for controlling the electrical current to the one or more light-emitting elements, the modulator for modulating the pulse width further comprising a M-bit programmable counter coupled to the N-bit adder.

6. The apparatus according to claim 1, wherein said apparatus operates at a cycle frequency greater than or equal to about 20 kHz.

7. The apparatus according to claim 6, wherein said apparatus operates at a cycle frequency of about 30 kHz.

8. An extended pulse width modulation method for transforming a (N+M)-bit signal into a stream of 2^M words of N-bit width for a total of 2^M pulse cycles, the method comprising the acts of:

a) receiving the (N+M)-bit signal that includes an N-bit word of N most significant bits having a value n represented by a first binary coded number, the value n having a maximum value of 2^N−

1, and an M-bit word of M least significant bits having a value m represented by a second binary coded number;

b) splitting the (N+M)-bit signal into an N-bit portion and an M-bit portion;

c) interpreting the N-bit portion as the first binary coded number having the value n;

d) interpreting the M-bit portion as the second binary coded number having the value m;

e) encoding a third binary coded number having a value n+1 in a form of a first binary N-bit word and feeding the first binary N-bit word for m pulse cycles into the stream; and

f) encoding the first binary coded number having the value n in a form of a second binary N-bit word for (2^M−

m) pulse cycles and feeding the second binary N-bit word into the stream when n<

2^N−

1 and n>

0;

thereby forming the stream of 2^M words of N-bit width for a total of 2^M pulse cycles, where N and M are integers greater than zero and N is greater than M.

9. An extended pulse width modulation apparatus for transforming a (N+M)-bit signal into a stream of 2^M words of N-bit width for a total of 2^M pulse cycles, the apparatus comprising:

an interface for receiving the (N+M)-bit signal that includes an N-bit word of N most significant bits having a value n represented by a first binary coded number, the value n having a maximum value of 2^N−

1, and an M-bit word of M least significant bits having a value m represented by a second binary coded number;

an interface for splitting the (N+M)-bit signal into an N-bit portion and an M-bit portion, for interpreting the N-bit portion as the first binary coded number having the value n and for interpreting the M-bit portion as the second binary coded number having the value m; and

a modulator for encoding a third binary coded number having a value n+1 in a form of a first binary N-bit word and feeding the first binary N-bit word for m pulse cycles into the stream, and for encoding the first binary coded number having the value n in a form of a second binary N-bit word for (2^M−

m) pulse cycles and feeding the second binary N-bit word into the stream when n<

2^N−

1 and n>

0;

thereby forming the stream of 2^M words of N-bit width for a total of 2^M pulse cycles, where N and M are integers greater than zero and N is greater than M.

10. An apparatus for controlling a light source comprising:

a pulse modulator configured to increase control resolution of the light source from 2^N to 2^N+M states, using an N+M input control signal to generate an N-bit pulse modulation signal; and

an N-bit controller configured to receive the N-bit pulse modulation signal for controlling the light source;

wherein the pulse modulator comprises;

an M-bit counter configured to receive an M-bit word of M least significant bits of the N+M input control signal, and to provide a counter output;

an N-bit adder configured to receive at a first input port an N-bit word of N most significant bits of the N+M input control signal, to receive at a second input port a logic bit, and to provide the N-bit pulse modulation signal to the N-bit controller;

a logic unit configured to receive the counter output and a combination of the N-bit word, and to provide the logic bit to the N-bit adder, where N and M are integers greater than zero and N is greater than M, wherein the logic unit sets the logic bit to zero when the N-bit word has a maximum value.

11. The apparatus of claim 10, further comprising an N-bit pulse width modulation for receiving the N-bit output from the N-bit adder for controlling the light source with a control resolution which is increased from 2^N to 2^N+M states based on the logic bit when a value n of the N-bit word is greater than zero and less than the maximum value.

12. The apparatus of claim 10, wherein remaining N−

1 lines of the second port are set to zero.

13. The apparatus of claim 10, wherein the M-bit word comprises least significant bits of the N+M input control signal.

14. The apparatus of claim 10, wherein the logic unit comprises an AND gate that outputs the logic bit, the AND gate having a first input and a second input, the first input of the AND gate being connected to an output of eight-input NAND gate that receives the N-bit word, and the second input receiving the counter output.

15. The apparatus of claim 14, wherein the counter output changes from a logical one to a logical zero when a value of the counter exceeds a number encoded in the M-bit word.