Stochastic signal density modulation for optical transducer control

• US 8,476,846 B1
• Filed: 02/23/2012
• Issued: 07/02/2013
• 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: Ess, David Van, Prendergast, Patrick N.
• Primary Examiner(s): A, Minh D
• Application Number:
  US13/403,242
• Time in Patent Office: 495 Days
• Field of Search: 315/224, 315/291, 315/307, 315/308, 315/312, 362/800, 362/611, 362/612, 362/555, 345/82, 345/204
• US Class Current: 315/308
• 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 controller for optical transducers uses stochastic signal density modulation to reduce electromagnetic interference.

Claims

1. A method of controlling one or more light emitting diodes (LEDs), comprising:

generating a stochastic signal density modulation signal;

controlling a light intensity output from the one or more LEDs by modulating a controllable current with the stochastic signal density modulation signal having a frequency greater than a uniform frequency modulation and free of spectral peaks, wherein the stochastic signal density modulation signal has a reduced electromagnetic interference content relative to the uniform frequency modulation; and

comparing a stochastic value to a programmed number to generate the stochastic signal density modulation signal.

2. The method of claim 1, comprising:

comparing a plurality of stochastic values with a stored number representing a signal density of the stochastic signal density modulation signal.

3. The method of claim 2, comprising:

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

4. The method of claim 2, wherein the plurality of stochastic values comprises a plurality of random numbers.

5. The method of claim 2, wherein the plurality of stochastic values comprises a plurality of pseudorandom numbers.

6. The method of claim 2, comprising:

programming the stored number representing the signal density of the stochastic signal density modulation signal.

7. An apparatus, comprising:

a stochastic signal density modulation circuit adapted to generate a stochastic signal density modulation signal;

a current control circuit adapted to control a light intensity output from one or more light emitting diodes by modulating a controllable current with the stochastic signal density modulation signal having a frequency greater than a uniform frequency modulation and free of spectral peaks, wherein the stochastic signal density modulation signal has a reduced electromagnetic interference content relative to the uniform frequency modulation; and

a comparator adapted to compare a state of a stochastic state machine to a programmed number to generate the stochastic signal density modulation signal.

8. The apparatus of claim 7, comprising:

a comparator adapted to compare a plurality of stochastic values from a stochastic state machine with a stored number representing a signal density of the stochastic signal density modulation signal.

9. The apparatus of claim 8, comprising

a pulse train generation circuit adapted to generate a pulse train to control the controllable current, wherein the pulse train includes one of a first pulse amplitude if a stochastic value of the plurality of stochastic values is greater than the programmed number and a second pulse amplitude if the stochastic value of the plurality of stochastic values is less than or equal to the programmed number.

10. The apparatus of claim 8, wherein the stochastic state machine comprises:

a random number generator, wherein the plurality of stochastic values comprises a plurality of random numbers.

11. The apparatus of claim 8, wherein the stochastic state machine comprises:

a pseudorandom number generator, wherein the plurality of stochastic values comprises a plurality of pseudorandom numbers.

12. The apparatus of claim 8, comprising:

a signal density register adapted to store the stored number.

13. The apparatus of claim 12, wherein the signal density register comprises a programmable register, and wherein the stored number comprises a programmed number.

14. A processing device, comprising:

a controllable current supply coupled to a light-emitting diode; and

a stochastic signal density modulator (SSDM) circuit coupled to the controllable current supply, wherein the SSDM circuit is configured to provide a stochastic control signal to the controllable current supply to control a light intensity output of the light-emitting diode and to reduce electromagnetic interference, and wherein the stochastic control signal comprises a signal density corresponding to a stored signal density value; and

a comparator adapted to compare a state of a stochastic state machine to a programmed number to provide the stochastic control signal.

15. The processing device of claim 14, comprising:

a signal density register adapted to store the stored signal density value.

16. The processing device of claim 15, wherein the signal density register comprises a programmable register, and wherein the stored signal density value comprises a programmed signal density value.