Photosensor arrangements
A photosensor arrangement may include an amplifier configured to receive charge from a photosensor device at a first input, and a second input configured to receive a first reference voltage. The amplifier may provide an output voltage on an output. A comparator has a first input at the output voltage, a second input at the first reference voltage and is configured to provide a compare output. A capacitor is configured to have a first plate coupled to the output of the amplifier and a second plate coupled to the first input of the comparator.
1. An electronic device comprising:
a photosensor device comprising a photodiode;
an amplifier having a first amplifier input, a second amplifier input and an amplifier output, the amplifier configured to receive a charge from the photosensor device on the first amplifier input, receive a first reference voltage on the second amplifier input, and provide an output voltage on the amplifier output;
a comparator having a first comparator input, a second comparator input and a comparator output, the comparator configured to receive the output voltage on the first comparator input, receive the first reference voltage on the second comparator input, and provide a compare output on the comparator output;
a feedback path between the comparator output and the first comparator input; and
a capacitor adjacent the photodiode and having a first plate and a second plate, with the capacitor configured to have the first plate coupled to the amplifier output and the second plate coupled to the first comparator input.
2. The electronic device according to claim 1 , further comprising reset circuitry configured to reset the amplifier and the comparator.
3. The electronic device according to claim 2 , wherein the amplifier and comparator are configured so that after reset thereof, the output voltage equals the first reference voltage plus an offset voltage, and a second voltage is at the first reference voltage.
4. The electronic device according to claim 1 , wherein the capacitor comprises a metal-dielectric-metal capacitor.
5. The electronic device according to claim 1 , further comprising reset circuitry coupled to the amplifier and comparator; and wherein the feedback path comprises a switch configured to be controlled by the reset circuitry.
6. The electronic device according to claim 1 , wherein the second comparator input is configured to receive one of the first reference voltage and a second reference voltage.
7. The electronic device according to claim 6 , wherein the second reference voltage is higher than the first reference voltage.
8. The electronic device according to claim 6 , wherein the second reference voltage is used when the photosensor device is being read.
9. The electronic device according to claim 8 , further comprising reset circuitry coupled to the amplifier and comparator; and circuitry having a first circuitry input and a second circuitry input, wherein the circuitry is configured to have the compare output received on the first circuitry input and a disable signal provided by the reset circuitry received on the second circuitry input, and wherein the circuitry is configured to prevent the compare output from being used to provide a count value when the reference voltage on the second comparator input is being changed from the first to second reference voltage.
10. The electronic device according to claim 9 , wherein the circuitry comprises a NOR gate.
11. The electronic device according to claim 1 , further comprising a feedback path between the amplifier output and the first amplifier input.
12. The electronic device according to claim 11 , further comprising reset circuitry coupled to the amplifier and comparator; and wherein the feedback path comprises a switch configured to be controlled by the reset circuitry.
13. The electronic device according to claim 1 , further comprising a semiconductor substrate; and wherein the photosensor device, amplifier, comparator and capacitor are formed on the semiconductor substrate so that the electronic device comprises an integrated circuit.
14. The electronic device according to claim 1 , wherein the photosensor device, amplifier, comparator and capacitor define a camera; and further comprising a display coupled to the camera.
15. An electronic device comprising:
a photosensor device comprising a photodiode;
an amplifier having a first amplifier input coupled to the photosensor device, a second amplifier input coupled to a first reference voltage, and an amplifier output;
a comparator having a first comparator input and a comparator output;
a feedback path between the comparator output and the first comparator input; and
a capacitor adjacent the photodiode and having a first plate coupled to the amplifier output, and a second plate coupled to the first comparator input.
16. The electronic device according to claim 15 , further comprising reset circuitry configured to reset the amplifier and the comparator.
17. The electronic device according to claim 16 , wherein the amplifier and comparator are configured so that after reset thereof, output voltage at the amplifier output equals the first reference voltage plus an offset voltage, and a second voltage is at the first reference voltage.
18. The electronic device according to claim 15 , wherein the capacitor comprises a metal-dielectric-metal capacitor.
19. The electronic device according to claim 15 , further comprising reset circuitry coupled to the amplifier and comparator; and wherein the feedback path comprises a switch configured to be controlled by the reset circuitry.
20. The electronic device according to claim 15 , wherein said comparator has a second comparator input configured to receive one of the first reference voltage and a second reference voltage.
21. The electronic device according to claim 20 , wherein the second reference voltage is higher than the first reference voltage.
22. The electronic device according to claim 20 , wherein the second reference voltage is used when the photosensor device is being read.
23. The electronic device according to claim 15 , further comprising a feedback path between the amplifier output and the first amplifier input.
24. The electronic device according to claim 23 , further comprising reset circuitry coupled to the amplifier and comparator; and wherein the feedback path comprises a switch configured to be controlled by the reset circuitry.
25. The electronic device according to claim 15 , further comprising a semiconductor substrate; and wherein the photosensor device, amplifier, comparator and capacitor are formed on the semiconductor substrate so that the electronic device comprises an integrated circuit.
26. The electronic device according to claim 15 , wherein the photosensor device, amplifier, comparator and capacitor define a camera; and further comprising a display coupled to the camera.
27. A method for making an electronic device comprising:
forming on a semiconductor substrate a photosensor device comprising a photodiode;
forming on the semiconductor substrate an amplifier having a first amplifier input coupled to the photosensor device, a second amplifier input coupled to a first reference voltage, and an amplifier output;
forming on the substrate a comparator having a first comparator input and a comparator output;
forming a feedback path between the comparator output and the first comparator input; and
forming on the substrate a capacitor adjacent the photodiode and having a first plate coupled to the amplifier output, and a second plate coupled to the first comparator input.
28. The method according to claim 27 , further comprising forming on the semiconductor substrate reset circuitry configured to reset the amplifier and the comparator.
29. The method according to claim 28 , wherein the amplifier and comparator are configured so that after reset thereof, output voltage at the amplifier output equals the first reference voltage plus an offset voltage, and a second voltage is at the first reference voltage.
30. An electronic device comprising:
a photosensor device comprising a photodiode;
an amplifier having a first amplifier input, a second amplifier input and an amplifier output, the amplifier configured to receive a charge from the photosensor device on the first amplifier input, receive a first reference voltage on the second amplifier input, and provide an output voltage on the amplifier output;
a comparator having a first comparator input, a second comparator input and a comparator output, the comparator configured to receive the output voltage on the first comparator input, receive the first reference voltage on the second comparator input, and provide a compare output on the comparator output;
a feedback path between the comparator output and the first comparator input;
a capacitor adjacent the photodiode and having a first plate and a second plate, the capacitor configured to have the first plate coupled to the amplifier output and the second plate coupled to the first comparator input;
reset circuitry coupled to the amplifier and comparator; and
circuitry having a first circuitry input and a second circuitry input, with the circuitry configured to have the comparator output received on the first circuitry input and a disable signal provided by the reset circuitry received on the second circuitry input.
31. The electronic device according to claim 30 , wherein the amplifier and comparator are configured so that after reset thereof, the output voltage equals the first reference voltage plus an offset voltage, and a second voltage is at the first reference voltage.
32. The electronic device according to claim 30 , wherein the feedback path comprises a switch configured to be controlled by the reset circuitry.
33. The electronic device according to claim 30 , wherein the second comparator input is configured to receive one of the first reference voltage and a second reference voltage, with the second reference voltage being higher than the first reference voltage.
34. The electronic device according to claim 33 , wherein the second reference voltage is used when the photosensor device is being read.
35. The electronic device according to claim 34 , wherein the circuitry is configured to prevent the compare output from being used to provide a count value when the reference voltage on the second comparator input is being changed from the first to second reference voltage.
36. The electronic device according to claim 35 , wherein the circuitry comprises a NOR gate.