LIGHT SENSOR

• US 20140224961A1
• Filed: 02/12/2013
• Published: 08/14/2014
• Est. Priority Date: 02/12/2013
• Status: Active Grant

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Bechtel, Jon H., McMillan, Daniel G., Reese, Spencer D., Nelson, Barry K
• Granted Patent: US 9,207,116 B2
• Time in Patent Office: Days
• US Class Current: 250/206
• CPC Class Codes: G01J 1/0403 Mechanical elements; Supports for optical elements; Scanning arrangements
• CPC Class Codes: G01J 1/26 adapted for automatic variation of the measured or reference value regulation of light intensity G05D25/00
• CPC Class Codes: G01J 1/4228 arrangements with two or more detectors, e.g. for sensitivity compensation
• CPC Class Codes: G01J 1/46 using a capacitor
• CPC Class Codes: G01J 2001/0276 Protection
• CPC Class Codes: H05B 47/11 by determining the brightness or colour temperature of ambient light
• CPC Class Codes: Y02B 20/40 Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

A light sensor is provided that includes an exposed light transducer for accumulating charge in proportion to light incident thereon over an integration period; and a light-to-pulse circuit in communication with the exposed light transducer, the light-to-pulse circuit operative to output a pulse having a pulse width based on the charge accumulated by the exposed light transducer. The light-to-pulse circuit may include a one shot logic circuit that contributes to generation of the pulse. The light sensor may include an input/output pad, a capacitor provided at the input/output pad for blocking static electricity, an input low pass filter provided at the input/output pad for blocking electromagnetic interference, and/or a bandgap voltage reference circuit connected to a power source having a supply voltage level in a range of about 3.3V to about 5.0V, and for generating a set of stable reference voltages throughout the supply voltage level range.

Claims

1. A light sensor comprising:

an exposed light transducer operative to accumulate charge in proportion to light incident on the exposed light transducer over an integration period;

a shielded light transducer shielded from light, the shielded light transducer having substantially the same construction as the exposed light transducer, the shielded light transducer operative to accumulate charge in proportion to noise over the integration period; and

a light-to-pulse circuit in communication with the exposed light transducer and the shielded light transducer, the light-to-pulse circuit operative to output a pulse having a pulse width based on the difference between the charges accumulated by the exposed and shielded light transducers, wherein the light-to-pulse circuit includes a one shot logic circuit that contributes to a generation of the pulse.

2. The light sensor of claim 1 and further comprising:

a light storage capacitor coupled to the exposed light transducer for outputting a light storage capacitor voltage corresponding to the accumulated charge of the exposed light transducer;

a noise storage capacitor coupled to the shielded light transducer for outputting a noise storage capacitor voltage corresponding to the accumulated charge of the shielded light transducer;

a ramp generator for generating a ramp voltage;

a first comparator for receiving the light storage capacitor voltage and the ramp voltage and for generating a light level output when the light storage capacitor voltage reaches the ramp voltage; and

a second comparator for receiving the noise storage capacitor voltage and the ramp voltage and for generating a noise level output when the noise storage capacitor voltage reaches the ramp voltage,

wherein the one shot logic circuit is coupled to receive the light level output and the noise level output and to generate the pulse responsive to the light level output and the noise level output.

3. The light sensor of claim 2, wherein the one shot logic circuit outputs the pulse any time either or both of the light storage capacitor voltage and the noise storage capacitor voltage reaches the ramp voltage.

4. The light sensor of claim 3, wherein the one shot logic circuit outputs a pulse of known length when either or both of the light storage capacitor voltage and the noise storage capacitor voltage reaches the ramp voltage.

5. The light sensor of claim 1 and further comprising an input/output pad and a capacitor provided at the input/output pad and connected between the input/output pad and ground for blocking static electricity.

6. The light sensor of claim 1 and further comprising an input/output pad and an input low pass filter provided at an input side of the input/output pad for blocking electromagnetic interference.

7. The light sensor of claim 1 and further comprising a bandgap reference circuit for receiving power from a power source having a supply voltage level in a range of about 3.3V to about 5.0V, and for generating a set of stable reference voltages throughout the supply voltage level range to the light-to-pulse circuit.

8. The light sensor of claim 1 and further comprising a bandgap voltage reference circuit for receiving power from a power source and for generating a set of stable reference voltages to the light-to-pulse circuit, wherein the bandgap voltage reference circuit generates constant currents from the supply voltage supplied by the power supply and wherein the bandgap voltage reference circuit comprises resistive ladders through which the constant currents are passed to generate the set of stable reference voltages.

9. A rearview assembly for a vehicle comprising:

a rearview device for providing a rearward view to a driver of the vehicle;

the light sensor of claim 1; and

a mounting mechanism adapted for mounting the rearview device and the light sensor to the vehicle.

10. The rearview assembly of claim 9 and further comprising a display carried by the mounting mechanism, and a display brightness control circuit coupled to the display and the light sensor package for controlling a brightness of the display in response to light levels sensed by the light sensor package.

11. The rearview assembly of claim 9 and further comprising an electro-optic mirror element carried by the mounting mechanism, and a mirror reflectivity control circuit coupled to the electro-optic mirror element and the light sensor package for controlling a reflectivity of the electro-optic mirror element in response to light levels sensed by the light sensor package.

12. A light sensor package comprising:

an enclosure having a window for receiving light, the enclosure admitting at least a power connection pad, a ground connection pad, and an input/output pad;

an input low pass filter provided at the input/output pad for blocking electromagnetic interference;

an exposed light transducer disposed within the enclosure, the exposed light transducer operative to accumulate charge in proportion to light received through the window incident on the exposed light transducer over an integration period; and

a light-to-pulse circuit in communication with the exposed light transducer, the light-to-pulse circuit operative to output a pulse on the output pin, the pulse width based on the charge accumulated by the exposed light transducer.

13. The light sensor package of claim 12, wherein the input low pass filter comprises a resistance at the input/output pad and a capacitor coupled between the resistance and ground.

14. The light sensor package of claim 13, wherein the capacitor is configured such that the light sensor package is rated for at least 2 kV static protection.

15. The light sensor package of claim 13, wherein the resistance is an integral part of the input/output pad.

16. The light sensor package of claim 12 and further comprising a nonvolatile memory within the enclosure for storing data from which calibration data may be obtained for the light sensor.

17. A light sensor comprising:

an exposed light transducer operative to accumulate charge in proportion to light incident on the exposed light transducer over an integration period;

a light-to-pulse circuit in communication with the exposed light transducer, the light-to-pulse circuit operative to output a pulse having a pulse width based on the charge accumulated by the exposed light transducer; and

a bandgap voltage reference circuit for receiving power from a power source and for generating a set of stable reference voltages to the light-to-pulse circuit, wherein the bandgap voltage reference circuit generates a constant current from the supply voltage supplied by the power supply and wherein the bandgap voltage reference circuit comprises a resistive ladder through which the constant current is passed to generate the set of stable reference voltages.

18. The light sensor of claim 17, wherein the bandgap voltage reference circuit generates a plurality of constant currents from the supply voltage supplied by the power supply and wherein the bandgap voltage reference circuit comprises a plurality of resistive ladders through which the constant currents are passed to generate the set of stable reference voltages.

19. A light sensor comprising:

an exposed light transducer operative to accumulate charge in proportion to light incident on the exposed light transducer over an integration period;

a light-to-pulse circuit in communication with the exposed light transducer, the light-to-pulse circuit operative to output a pulse having a pulse width based on the charge accumulated by the exposed light transducer; and

a bandgap voltage reference circuit for receiving power from a power source having a supply voltage level in a range of about 3.3V to about 5.0V, and for generating a set of stable reference voltages throughout the supply voltage level range to the light-to-pulse circuit.

20. The light sensor of claim 19, wherein the bandgap voltage reference circuit generates constant currents from the supply voltage supplied by the power supply and wherein the bandgap voltage reference circuit comprises resistive ladders through which the constant currents are passed to generate the set of stable reference voltages.