Light monitor, electronic circuit incorporating a light monitor, and method of making the same

• US 7,265,332 B2
• Filed: 06/16/2005
• Issued: 09/04/2007
• Est. Priority Date: 11/11/2004
• Status: Active Grant

• Current Assignee: STMicroelectronics Limited (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Limited (STMicroelectronics NV)
• Inventors: Raynor, Jeffrey, Baxter, Patrick
• Primary Examiner(s): Luu; Thanh X.
• Application Number:
  US11/154,222
• Publication Number:
  US 20060097136A1
• Time in Patent Office: 810 Days
• Field of Search: 250/214.A, 250/214.DC, 341/133, 341/164
• US Class Current: 250/214.0DC
• CPC Class Codes: G01J 1/32 adapted for automatic variation of the measured or reference value regulation of light intensity G05D25/00
• CPC Class Codes: G01J 1/46 using a capacitor

Abstract

A light monitor includes a single semiconductor substrate. A light to frequency (LTF) converter is on the single semiconductor substrate, a threshold comparator is on the single semiconductor substrate and coupled to an output of the light to frequency converter, and a light intensity calculator is on the single semiconductor substrate and coupled to an output of the threshold comparator.

Claims

1. A light monitor comprising:

a single semiconductor, substrate;

a light to frequency (LTF) converter on said single semiconductor substrate for providing a pulsed signal representing an intensity of incident light;

a light intensity calculator on said single semiconductor substrate and coupled to an output of said LTF converter, said light intensity calculator comprising

a clock signal generator for providing a clock signal, and

a counter for incrementing a measurement variable based upon the clock signal, the measurement variable being reset between each pulse received from said LTF converter; and

said light intensity calculator scaling a signal generated by said LTF converter in accordance with the clock signal, and accumulating a resulting scaled signal in said counter for calculating a scaled measurement variable; and

a threshold comparator on said single semiconductor substrate and coupled to an output of said light intensity calculator.

2. A light monitor according to claim 1, wherein said clock signal generator comprises:

a current source; and

a charge sensing amplifier circuit coupled to said current source and comprising a first feedback capacitor.

3. A light monitor according to claim 1, wherein said clock signal generator comprises a crystal oscillator;

and wherein said light intensity calculator further comprises;

a reference signal generator for generating a reference signal; and

said counter accumulating the reference signal for calculating a reference variable.

4. A light monitor according to claim 3, wherein said counter comprises a gain adjustment calculator for calculating a gain adjustment that includes deviation between the reference variable and an expected value of the reference variable.

5. A light monitor according to claim 4, wherein said counter adjusts the measurement variable in accordance with the gain adjustment.

6. A light monitor according to claim 1, wherein said threshold comparator comprises at least one register for containing a value of a first limit variable, and compares a value of the measurement variable from said light intensity calculator with a value of the first limit variable.

7. A light monitor according to claim 6, wherein said threshold comparator outputs to an external system an indicator of whether the value of the measurement variable exceeds the value of the first limit variable.

8. A light monitor according to claim 7, wherein said threshold comparator comprises a single output pin for outputting the indicator to the external system.

9. A light monitor according to claim 1, wherein said threshold comparator comprises a plurality of registers for containing a value of a first limit variable and a second limit variable, said threshold comparator comparing a value of the measurement variable with a value of the first limit variable and the second limit variable.

10. A light monitor according to claim 9, wherein said threshold comparator outputs to an external system an indicator of whether the value of the measurement variable

exceeds the value of the first limit variable;

is less than the value of the second limit variable;

or

is between the values of the first limit variable and the second limit variable.

11. A light monitor according to claim 9, wherein said threshold comparator comprises outputs coupled to a bi-directional interface.

12. A light monitor according to claim 11, wherein the bi-directional interface comprises at least one of an I2C interface, an SPI interface and a CAN interface.

13. A light monitor according to claim 11, wherein the bi-directional interface comprises a wireless interface.

14. A light monitor according to claim 13, wherein the wireless interface comprises a Zigbee interface.

15. A light monitor according to claim 11, wherein said threshold comparator outputs the values of the first and second limit variables to said plurality of registers through said bi-directional interface.

16. An electronic device comprising:

a light source for generating light;

a light monitor for receiving incident light and comprising

a single semiconductor substrate,

a light to frequency (LTF) converter on said single semiconductor substrate for providing a pulsed signal representing an intensity of the incident light,

a light intensity calculator on said single semiconductor substrate and coupled to an output of said LTV converter, said light intensity calculator comprising

a clock signal generator for providing a clock signal, and

a counter for incrementing a measurement variable based upon the clock signal, the measurement variable being reset between each pulse received from said LTF converter;

a threshold comparator on said single semiconductor substrate and coupled to an output of said light intensity calculator and comprising at least one register for containing a value of a first limit variable, and for comparing a value of the measurement variable from said light intensity calculator with a value of the first limit variable; and

a controller having an input for receiving the pulsed signal representing the intensity of the incident light from said light monitor, and providing a control signal to said light source in response thereto;

said light source altering the generated light based upon the control signal.

17. An electronic device according to claim 16, wherein said clock signal generator comprises:

a current source; and

a charge sensing amplifier circuit coupled to said current source and comprising a first feedback capacitor.

18. An electronic device according to claim 16, wherein said light intensity calculator scales a signal generated by said LTF converter in accordance with the clock signal, and accumulates a resulting scaled signal in said counter for calculating a scaled measurement variable.

19. An electronic device according to claim 16, wherein said clock signal generator comprises a crystal oscillator;

and wherein said light intensity calculator further comprises;

a reference signal generator for generating a reference signal; and

a crystal oscillator whose output provides a clock signal to said counter;

said counter accumulating the reference signal for calculating a reference variable.

20. An electronic device according to claim 16, wherein said threshold comparator comprises a plurality of registers for containing the value of the first limit variable and a value of a second limit variable, and for comparing the value of the measurement variable with the values of the first and limit variables.

21. An electronic device according to claim 16, wherein said light source, said light monitor and said controller define a lighting control system for at least one of a portable computing device back-light control system, a mobile telecommunications device back-light control system, a street lighting control system, and an automotive lighting control system.

22. A method for making a light monitor comprising;

forming on a single semiconductor substrate a light to frequency (LTF) converter for providing a pulsed signal representing an intensity of incident light, a light intensity calculator coupled to an output of the LTF converter, and a threshold comparator coupled to an output of the light intensity calculator, the light intensity calculator comprising

a clock signal generator for providing a clock signal, the clock signal generator comprising a current source, and a charge sensing amplifier circuit coupled to the current source and comprising a first feedback capacitor, and

a counter for incrementing a measurement variable based upon the clock signal, the measurement variable being reset between each pulse received from the LTF converter.

23. A method according to claim 22, wherein the light intensity calculator scales a signal generated by the LTF converter in accordance with the clock signal, and accumulates a resulting scaled signal in the counter for calculating a scaled measurement variable.

24. A method according to claim 22, wherein forming the light intensity calculator further comprises forming a reference signal generator for generating a reference signal, and wherein the counter accumulates the reference signal for calculating a reference variable.

25. A method according to claim 22, wherein forming the threshold comparator comprises forming at least one register for containing a value of a first limit variable, the threshold comparator for comparing a value of the measurement variable from the light intensity calculator with a value of the first limit variable.

26. A method according to claim 22, wherein forming the threshold comparator comprises forming a plurality of registers for containing a value of a first limit variable and a second limit variable, the threshold comparator for comparing a value of the measurement variable with a value of the first limit variable and the second limit variable.