Photodiode light sensor

• US 6,359,274 B1
• Filed: 05/07/1999
• Issued: 03/19/2002
• Est. Priority Date: 01/25/1999
• Status: Expired due to Term

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Fossum, Eric R., Bechtel, Jon H., Nixon, Robert H.
• Primary Examiner(s): EVANS, FANNIE L
• Application Number:
  US09/307,191
• Time in Patent Office: 1,047 Days
• Field of Search: 250/214.R, 250/214.C, 250/214.1, 250/215, 359/601, 359/602, 359/603, 359/604, 359/605, 359/606, 359/607, 359/608, 327/514
• US Class Current: 250/214.00C
• CPC Class Codes: B60R 1/088 using a cell of electrically changeable optical characteristic, e.g. liquid-crystal or electrochromic mirrors
• CPC Class Codes: G01J 1/0488 with spectral filtering
• CPC Class Codes: G01J 1/4228 arrangements with two or more detectors, e.g. for sensitivity compensation
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01J 1/46 using a capacitor
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 31/101 Devices sensitive to infrared, visible or ultraviolet radiation
• CPC Class Codes: H01L 33/54 having a particular shape

Abstract

Light sensors having a wide dynamic range are used in a variety of applications. A wide dynamic range light sensor includes an exposed photodiode light transducer accumulating charge in proportion to light incident over an integration period. Sensor logic determines a light integration period prior to the beginning of integration and the charge is reset. Charge accumulated by the exposed light transducer over the light integration period is measured and a pulse having a width based on the accumulated charge is determined.

Claims

1. A light sensor comprising:

a photodiode light transducer exposed to light, the exposed light transducer operative to accumulate charge in proportion to light incident over an integration period; and

a sensor logic in communication with the exposed light transducer, the sensor logic operative to

(a) determine a light integration period prior to the beginning of integration,

(b) reset the charge accumulated in the exposed light transducer at the beginning of the determined light integration period,

(c) measure the charge accumulated by the exposed light transducer over the determined light integration period, and

(d) determine a pulse having a width based on the measured accumulated exposed light transducer charge.

2. A light sensor as in claim 1 further comprising a comparator with one input connected to the exposed light transducer and the other input connected to a switched capacitor circuit, the switched capacitor circuit operable to charge a capacitor to a fixed voltage when the switch is closed and to discharge the capacitor at a constant rate when the switch is open, wherein the sensor logic is further operative to close the switch during the determined light integration period and open the switch after the determined light integration period, thereby creating the pulse at the comparator output.

3. A light sensor as in claim 2 further comprising a second comparator with one input connected to a fixed voltage and the other input connected to the switched capacitor circuit, the second comparator output operative to inhibit output of the determined pulse if the ramp voltage is less than the fixed voltage.

4. A light sensor as in claim 1 further comprising a photodiode light transducer shielded from light, the shielded light transducer operative to accumulate charge in proportion to noise over the integration period, wherein the sensor logic is further operative to:

reset the charge accumulated in the shielded light transducer at the beginning of the determined light integration period;

measure the charge accumulated by the shielded light transducer over the determined light integration period; and

determine an output pulse having a width based on the difference between the measured accumulated exposed light transducer charge and the measured accumulated shielded light transducer charge.

5. A light sensor as in claim 4 wherein the light sensor has an input for receiving an integration signal and wherein the noise is dependent on the light sensor temperature, the sensor logic further operable to:

determine an integration period based on the integration signal; and

output the output pulse after a time length following the end of the integration signal, the time length based on the noise level, the time length thereby indicating the light sensor temperature.

6. A light sensor as in claim 1 wherein the light integration period is determined from the asserted portion of a control signal received by the sensor logic.

7. A light sensor as in claim 1 wherein the sensor control is operative to determine each light integration period by cycling through a sequence of predetermined time periods.

8. A light sensor as in claim 1 further comprising at least one additional exposed photodiode light transducer, each additional exposed light transducer operative to accumulate charge in proportion to light incident over an integration period at a rate different than the rate of any other exposed light transducer, the sensor logic further operative to:

reset the charge accumulated in each of the at least one additional exposed light transducer at the beginning of the determined light integration period;

measure the charge accumulated by each of the at least one additional exposed light transducer over the determined light integration period; and

output a pulse having a width based on the measured accumulated charge for each of the at least one additional exposed light transducer.

9. A light sensor as in claim 8 wherein each exposed light transducer has a different collector area thereby having a different charge accumulation rate.

10. A light sensor as in claim 8 wherein each exposed light transducer has an aperture for admitting light incident on the sensor, each sensor aperture having a different admitting area thereby giving each exposed light transducer a different charge accumulation rate.

11. A light sensor as in claim 1 wherein the light transducer comprises:

a photodiode overlaying a substrate, the photodiode operative to accumulate incident charge in a photodiode well formed in a region of the substrate underlying the photodiode, the photodiode having an intrinsic photodiode capacitance;

a floating diffusion formed in the substrate, the floating diffusion having a diffusion well formed in a region of the substrate underlying the floating diffusion when the charge is reset, the floating diffusion operative to eliminate charge in the diffusion well when the charge is reset, the floating diffusion charge determining an output potential, the floating diffusion having an intrinsic floating diffusion capacitance; and

a transmission gate between the photodiode and the floating diffusion, the trasmission gate defining a transmission well formed in a region of the substrate between the region of the substrate underlying the photodiode and the region of the substrate underlying the floating diffusion, the transmission well having a depth shallower than the photodiode well and the diffusion well, the transmission gate having an intrinsic transmission gate capacitance;

wherein, when the charge is reset, charge in the photodiode well above the depth of the transmission well flows through the transmission well, through the floating diffusion, and is eliminated; and

wherein, during the determined light integration period, charge produced by light incident on the photodiode flows through the transmission well and into the diffusion well, producing output voltage inversely proportional to the floating diffusion capacitance, until the diffusion well is filled to the depth of the transmission well wherein charge produced by light incident on the photodiode fills the photodiode well, the transmission well, and the diffusion well, producing output voltage inversely proportional to the sum of the floating diffusion capacitance, the photodiode capacitance, and the transmission gate capacitance;

thereby providing a first sensitivity during charge accumulation in the diffusion well only and a second sensitivity during charge accumulation in the diffusion well, the transmission well, and the photodiode well, the first sensitivity greater than the second sensitivity.

12. A light sensor as in claim 11 further comprising an anti-bloom gate between the photodiode and a source voltage diffusion, the anti-bloom gate defining an anti-blooming well formed in a region of the substrate between the region of the substrate underlying the photodiode and the source voltage diffusion, the anti-blooming well having a depth shallower than the transmission well.

13. A light sensor package comprising:

an enclosure having a window for receiving light, the enclosure admitting a power pin, a ground pin, and an output pin;

an exposed photodiode 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;

a light-to-voltage circuit disposed within the enclosure and in communication with the exposed light transducer, the light-to-voltage circuit operative to output a light voltage signal based on charge accumulated by the exposed light transducer; and

a voltage-to-pulse circuit disposed within the enclosure and in communication with the light-to-voltage circuit, the voltage-to-pulse circuit operative to output a pulse on the output pin, the pulse width based on the light voltage signal.

14. A light sensor package as in claim 13 further comprising:

a photodiode light transducer shielded from light, the shielded light transducer having 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 noise-to-voltage circuit disposed within the enclosure and in communication with the shielded light transducer, the noise-to-voltage circuit operative to output a noise voltage signal based on charge accumulated by the shielded light transducer;

wherein the voltage-to-pulse circuit is operative to output a pulse on the output pin having a pulse width based on the difference between the light voltage signal and the noise voltage signal.

15. A light sensor package as in claim 13 further comprising a sensor logic disposed within the enclosure and in communication with exposed light transducer and the light-to-voltage circuit, the sensor logic operative to:

determine a light integration period;

reset the charge accumulated in the exposed light transducer at the beginning of the determined light integration period; and

control the accumulation of charge by the exposed light transducer during the determined light integration period.

16. A light sensor package as in claim 15 wherein the sensor logic is operative to determine the light integration period from the asserted portion of a control signal received on the output pin.

17. A light sensor package as in claim 15 wherein the sensor logic is operative to determine each light integration period by cycling through a sequence of predetermined time periods.

18. A light sensor package as in claim 15 further comprising at least one additional exposed photodiode light transducer, each additional exposed light transducer operative to accumulate charge in proportion to light incident over an integration period at a rate different than the rate of any other exposed light transducer, the sensor logic further operative to:

reset the charge accumulated in the at least one additional exposed light transducer at the beginning of the determined light integration period;

measure the charge accumulated by the at least one additional exposed light transducer over the determined light integration period; and

output a pulse having a width based on the measured accumulated charge for each of the at least one additional exposed light transducer.

19. A light sensor package as in claim 18 wherein each exposed light transducer has a different collector area thereby having a different charge accumulation rate.

20. A light sensor package as in claim 18 wherein each exposed light transducer has an aperture for admitting light incident on the sensor, each sensor aperture having a different admitting area thereby giving each exposed light transducer a different charge accumulation rate.

21. A light sensor comprising:

a photodiode overlaying a substrate, the photodiode operative to accumulate charge generated by light incident on the photodiode in a photodiode well formed in a region of the substrate underlying the photodiode, the photodiode having an intrinsic photodiode capacitance;

a floating diffusion formed in the substrate, the floating diffusion having a diffusion well formed in a region of the substrate underlying the floating diffusion when the charge is reset, the floating diffusion operative to eliminate charge in the diffusion well when the charge is reset, the floating diffusion charge determining an output potential, the floating diffusion having an intrinsic floating diffusion capacitance; and

a transmission gate between the photodiode and the floating diffusion, a transmission well formed in a region of the substrate between the region of the substrate underlying the photodiode and the region of the substrate underlying the floating diffusion, the transmission well having a depth shallower than the photodiode well and the diffusion well, the transmission gate having an intrinsic transmission gate capacitance;

wherein, when the charge is reset, charge in the photodiode well above the depth of the transmission well flows through the transmission well, through the floating diffusion, and is eliminated; and

wherein, during a light integration period, charge produced by light incident on the photodiode flows through the transmission well and into the diffusion well, producing output voltage inversely proportional to the floating diffusion capacitance, until the diffusion well is filled to the depth of the transmission well wherein charge produced by light incident on the photodiode fills the photodiode well, the transmission well, and the diffusion well, producing output voltage inversely proportional to the sum of the floating diffusion capacitance, the photodiode capacitance, and the transmission gate capacitance;

thereby providing a first sensitivity during charge accumulation in the diffusion well only and a second sensitivity during charge accumulation in the diffusion well, the transmission well, and the photodiode well, the first sensitivity greater than the second sensitivity.

22. A light sensor as in claim 21 further comprising an anti-bloom gate between the photodiode and a source voltage diffusion, the anti-bloom gate defining an anti-blooming well formed in a region of the substrate between the region of the substrate underlying the photodiode and the source voltage diffusion, the anti-blooming well having a depth shallower than the transmission well.