Light monitor, electronic circuit incorporating a light monitor, and method of making the same
View Patent ↗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.
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.