Stochastic signal density modulation for optical transducer control

• US 9,226,355 B1
• Filed: 07/02/2013
• Issued: 12/29/2015
• Est. Priority Date: 11/13/2006
• Status: Active Grant

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Van Ess, David, Prendergast, Patrick
• Primary Examiner(s): A, Minh D
• Application Number:
  US13/934,032
• Time in Patent Office: 910 Days
• Field of Search: 315/224, 315/291, 315/307, 315/317, 315/318, 315/299
• US Class Current: 1/1
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/18 using temperature feedback
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/30 Driver circuits
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines

Abstract

A current supply is coupled to a light source. The current supply is further coupled to a controller. The controller is configured to provide a stochastic control signal to the current supply, wherein the stochastic control signal controls a light intensity output of the light source.

Claims

1. An apparatus, comprising:

a current supply coupled to a light source; and

a controller coupled to the current supply including;

a comparator comprising a first input, a second input and an output,

a stochastic state machine, coupled to the first input of the comparator, to generate a plurality of stochastic values, and

a signal density register, coupled to the second input of the comparator, to hold a signal density value,

wherein the output of the comparator is based on a stochastic value of the plurality of stochastic values and the signal density value,

wherein the controller is configured to provide a stochastic control signal to the current supply, the stochastic control signal to control a light intensity output of the light source.

2. The apparatus of claim 1, wherein the stochastic state machine comprises a stochastic counter.

3. The apparatus of claim 1, wherein the stochastic state machine includes a machine-readable medium containing data that causes the stochastic state machine to perform operations comprising generating a sequence of pseudorandom numbers.

4. The apparatus of claim 1, wherein the current supply is configured to provide a first current level when the output of the comparator is a first output value and to provide a second current level when the output of the comparator is a second output value, wherein the output of the comparator is the first output value if a stochastic value of the plurality of stochastic values is greater than the signal density value and wherein the output of the comparator is the second output value if the stochastic value of the plurality of stochastic values is less than or equal to the signal density value.

5. The apparatus of claim 4, wherein the first current level comprises a non-zero current level and the second current level is approximately zero.

6. The apparatus of claim 4, wherein the second current level comprises a non-zero current level and the first current level is approximately zero.

7. The apparatus of claim 1, wherein the light source comprises an anode and a cathode, wherein a first terminal of the current supply is coupled to the anode, and wherein the current supply is configured to source current to the light source.

8. The apparatus of claim 1, wherein the light source comprises an anode and a cathode, wherein a first terminal of the current supply is coupled to the cathode, and wherein the current supply is configured to sink current from the light source.

9. A method, comprising:

providing a current for a light source; and

stochastically controlling the current to select a light intensity output from the light source, wherein stochastically controlling the current comprises;

comparing a state of a stochastic state machine to a signal density value to generate a stochastic signal density modulation signal;

generating the stochastic signal density modulation signal; and

modulating the current with the stochastic signal density modulation signal.

10. The method of claim 9, wherein generating the stochastic signal density modulation signal comprises:

comparing a plurality of stochastic values from the stochastic state machine with a programmed number representing a signal density of the stochastic signal density modulation signal; and

generating a pulse train to control the current, the pulse train having a first pulse amplitude if a stochastic value of the plurality of stochastic values is greater than the programmed number and having a second pulse amplitude if the stochastic value of the plurality of stochastic values is less than or equal to the programmed number.

11. The method of claim 10, wherein the stochastic state machine comprises a random number generator, wherein the plurality of stochastic values comprises a plurality of random numbers.

12. The method of claim 10, wherein the stochastic state machine comprises a pseudorandom number generator, wherein the plurality of stochastic values comprises a plurality of pseudorandom numbers.

13. The method of claim 12, further comprising programming the number representing the signal density of the stochastic signal density modulation signal in a programmable register.

14. The method of claim 10, further comprising:

providing a first current level to the light source when the pulse train has the first pulse amplitude; and

providing a second current level to the light source when the pulse train has the second pulse amplitude.

15. A system, comprising:

a plurality of current supplies coupled to a plurality of optical transducers; and

a plurality of controllers coupled to the plurality of current supplies, wherein each controller of the plurality of controllers is configured to provide a stochastic control signal to one of the current supplies, the stochastic control signal to control a light intensity output of one of the plurality of optical transducers.

16. The system of claim 15, wherein the plurality of optical transducers comprises a set of primary color optical transducers and wherein the plurality of controllers is configured to control a color mix of the plurality of optical transducers.

17. The system of claim 15, wherein the plurality of optical transducers comprises a set of secondary color optical transducers and wherein the plurality of controllers is configured to control a color mix of the plurality of optical transducers.

18. The system of claim 15, wherein the plurality of optical transducers comprises a set of complementary color optical transducers and wherein the plurality of controllers is configured to control a color mix of the plurality of optical transducers.