Dual conversion gain imagers

• US 20040251394A1
• Filed: 06/11/2003
• Published: 12/16/2004
• Est. Priority Date: 06/11/2003
• Status: Active Grant

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Hong, Sungkwon, Rhodes, Howard E.
• Granted Patent: US 7,075,049 B2
• Time in Patent Office: Days
• US Class Current: 250/208.1
• CPC Class Codes: H01L 27/14603 Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
• CPC Class Codes: H04N 25/587 acquired sequentially, e.g. using the combination of odd and even image fields
• CPC Class Codes: H04N 25/59 by controlling the amount of charge storable in the pixel, e.g. modification of the charge conversion ratio of the floating node capacitance
• CPC Class Codes: H04N 25/771 comprising storage means other than floating diffusion

Abstract

An imager with dual conversion gain floating diffusion regions. The dual conversion gain regions yield (1) high conversion gain and sensitivity to achieve excellent low light performance and (2) high full well capacity and conversion gain to achieve high dynamic range. A dual conversion gain element is coupled between each floating diffusion node and a respective capacitor. The dual conversion gain element switches in the capacitance of the capacitor to change the conversion gain of the floating diffusion node from a first conversion gain to a second conversion gain. The imager may be a CMOS or CCD type imager.

Claims

1. An imager device, comprising:

a diffusion region, connected to receive stored charge from a photosensitive device; and

a circuit connected to said diffusion region, said circuit providing said diffusion region with at least a dual conversion gain switchable between first and second conversion gains.

2. The imager device of claim 1 wherein said circuit is controlled to change the first conversion gain to the second conversion gain and to change the second conversion gain to the first conversion gain.

3. The imager device of claim 2, wherein said circuit comprises:

a capacitive element; and

a dual conversion gain element, said dual conversion gain element being controlled to connect said capacitive element to said diffusion region such that said diffusion region obtains the second conversion gain.

4. The imager device of claim 3, wherein said diffusion region has a first capacitance associated with the first conversion gain, said capacitive element has a second capacitance, and a combination of the first and second capacitances is associated with the second conversion gain.

5. The imager device of claim 4, wherein the photosensitive device has a capacitance greater than the first capacitance and less than the combination of the first and second capacitances.

6. The imager device of claim 3, wherein said dual conversion gain element is a transistor having a gate connected to receive a dual conversion gain control signal.

7. The imager device of claim 3, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said transistor is connected between said floating diffusion region and a first terminal of said capacitor, and a second terminal of said capacitor is connected to a supply voltage.

8. The imager device of claim 3, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said transistor is connected between said floating diffusion region and a first terminal of said capacitor, and a second terminal of said capacitor is connected to a ground potential.

9. The imager device of claim 3, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said capacitor is connected between said floating diffusion region and a first source/drain terminal of said transistor, and a second source/drain terminal of said transistor is connected to a supply voltage.

10. The imager device of claim 3, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said capacitor is connected between said floating diffusion region and a first source/drain terminal of said transistor, and a second source/drain terminal of said transistor is connected to a ground potential.

11. The imager device of claim 1, wherein said circuit is controlled based on an amount of stored charge detected in said device.

12. The imager device of claim 1, wherein said imager device is a complementary metal oxide semiconductor imager.

13. The imager device of claim 1, wherein said imager device is a charge coupled device imager.

14. The imager device of claim 1, wherein said circuit is connected to a supply voltage of an imager pixel array.

15. The imager device of claim 1, wherein said circuit is connected to a ground potential.

16. The imager device of claim 1, wherein said circuit provides said diffusion region with more than two conversion gains.

17. The imager device of claim 1, further comprising sample and hold circuitry for sampling and holding a reference output and multiple pixel signal outputs from said diffusion region.

18. A CMOS imager pixel, comprising:

a photosensor for accumulating stored charge;

a diffusion region, connected to receive the charge from the photosensor, said diffusion region having a first conversion gain; and

a conversion gain altering circuit connected to said diffusion region, said conversion gain altering circuit being controlled to change the first conversion gain to the second conversion gain and to change the second conversion gain to the first conversion gain.

19. The CMOS imager pixel of claim 18, wherein said photosensor has a first capacitance and said diffusion region has a second capacitance that is less than the first capacitance.

20. The CMOS imager pixel of claim 18, wherein said photosensor is a photodiode.

21. The CMOS imager pixel of claim 18, wherein said photosensor is a photodiode connected to a capacitor.

22. The CMOS imager pixel of claim 18, wherein said photosensor is a photogate.

23. The CMOS imager pixel of claim 18, wherein said photosensor is a photoconductor.

24. The CMOS imager pixel of claim 18, wherein said conversion gain altering circuit comprises:

a capacitive clement; and

a dual conversion gain element, said dual conversion gain element being controlled to connect said capacitive element to said diffusion region such that said diffusion region obtains the second conversion gain.

25. The CMOS imager pixel of claim 24, wherein said diffusion region has a first capacitance associated with the first conversion gain, said capacitive element has a second capacitance, and a combination of the first and second capacitances is associated with the second conversion gain.

26. The CMOS imager pixel of claim 24, wherein said photosensor has a capacitance greater than the first capacitance and less than the combination of the first and second capacitances.

27. The CMOS imager pixel of claim 24, wherein said dual conversion gain element is a transistor having a gate connected to receive a dual conversion gain control signal.

28. The CMOS imager pixel of claim 24, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said transistor is connected between said floating diffusion region and a first terminal of said capacitor, and a second terminal of said capacitor is connected to a supply voltage.

29. The CMOS imager pixel of claim 24, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said transistor is connected between said floating diffusion region and a first terminal of said capacitor, and a second terminal of said capacitor is connected to a ground potential.

30. The CMOS imager pixel of claim 24, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said capacitor is connected between said floating diffusion region and a first source/drain terminal of said transistor, and a second source/drain terminal of said transistor is connected to a supply voltage.

31. The CMOS imager pixel of claim 24, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said capacitor is connected between said floating diffusion region and a first source/drain terminal of said transistor, and a second source/drain terminal of said transistor is connected to a ground potential.

32. The CMOS imager pixel of claim 18, wherein the first conversion gain is used during low light conditions and the second conversion gain is used during bright light conditions.

33. The CMOS imager pixel of claim 18, wherein said conversion gain altering circuit is connected to a supply voltage of an imager pixel array.

34. The CMOS imager pixel of claim 18, wherein said conversion gain altering circuit is connected to a ground potential.

35. The CMOS imager pixel of claim 18, further comprising sample and hold circuitry for sampling and holding a reference output and multiple pixel signal outputs from said diffusion region.

36. A CMOS imager pixel, comprising:

a photosensor for accumulating stored charge;

a first transistor being controlled to reset said pixel;

a second transistor being controlled to transfer the stored charge from the photosensor;

a diffusion region, connected to receive the charge from said second transistor, said diffusion region having a first conversion gain;

a capacitive element; and

a third transistor coupled between said diffusion region and said capacitive element, said third transistor being controlled to connect said capacitive element to said diffusion region such that said diffusion region obtains at least a second conversion gain.

37. The CMOS imager pixel of claim 36, wherein said capacitive element is further coupled to a supply voltage.

38. The CMOS imager pixel of claim 36, wherein said capacitive element is further coupled to a ground potential.

39. The CMOS imager pixel of claim 36, further comprising:

a second capacitive element; and

a fourth transistor coupled between said diffusion region and said second capacitive element, said fourth transistor being controlled to connect said second capacitive element to said diffusion region such that said diffusion region obtains at least a third conversion gain.

40. A CMOS imager pixel, comprising:

a photosensor for accumulating stored charge;

a first transistor being controlled to reset said pixel;

a second transistor being controlled to transfer the stored charge from the photosensor;

a diffusion region, connected to receive the charge from said second transistor, said diffusion region having a first conversion gain;

a third transistor; and

a capacitive element coupled between said diffusion region and said third transistor, said third transistor being controlled to connect said capacitive element to said diffusion region such that said diffusion region obtains at least a second conversion gain.

41. The CMOS imager pixel of claim 40, wherein said third transistor is further coupled to a supply voltage.

42. The CMOS imager pixel of claim 40, wherein said third transistor is further coupled to a ground potential.

43. The CMOS imager pixel of claim 40, further comprising:

a fourth transistor; and

a second capacitive element coupled between said diffusion region and said fourth transistor, said fourth transistor being controlled to connect said second capacitive element to said diffusion region such that said diffusion region obtains at least a third conversion gain.

44. A CMOS imager pixel, comprising:

a photosensor for accumulating stored charge;

a first transistor being controlled to reset said pixel;

a diffusion region, connected to receive the charge from said photosensor, said diffusion region having a first conversion gain;

a capacitive element; and

a second transistor coupled between said diffusion region and said capacitive element, said second transistor being controlled to connect said capacitive element to said diffusion region such that said diffusion region obtains a second conversion gain.

45. The CMOS imager pixel of claim 44, wherein said capacitive element is further coupled to a supply voltage.

46. The CMOS imager pixel of claim 44, wherein said capacitive element is further coupled to a ground potential.

47. The CMOS imager pixel of claim 44 further comprising:

a second capacitive element; and

a third transistor coupled between said diffusion region and said second capacitive element, said third transistor being controlled to connect said second capacitive element to said diffusion region such that said diffusion region obtains at least a third conversion gain.

48. A CMOS imager pixel, comprising:

a photosensor for accumulating stored charge;

a first transistor being controlled to reset said pixel;

a diffusion region, connected to receive the charge from said photosensor, said diffusion region having a first conversion gain;

a second transistor; and

a capacitive element coupled between said diffusion region and said second transistor, said second transistor being controlled to connect said capacitive element to said diffusion region such that said diffusion region obtains a second conversion gain.

49. The CMOS imager pixel of claim 48, wherein said second transistor is further coupled to a supply voltage.

50. The CMOS imager pixel of claim 48, wherein said second transistor is further coupled to a ground potential.

51. The CMOS imager pixel of claim 48 further comprising:

a third transistor; and

a second capacitive element coupled between said diffusion region and said third transistor, said third transistor being controlled to connect said second capacitive element to said diffusion region such that said diffusion region obtains at least a third conversion gain.

52. A CCD imager comprising:

a register for inputting and outputting photo-generated charge;

a diffusion region, connected to receive the photo-generated charge from

said register, said diffusion region having a first conversion gain; and

a conversion gain altering circuit connected to said diffusion region, said conversion gain altering circuit being controlled to change the first conversion gain to the second conversion gain and to change the second conversion gain to the first conversion gain.

53. The imager of claim 52, wherein the first conversion gain is used during low light conditions and the second conversion gain is used during bright light conditions.

54. The imager of claim 52, wherein said conversion gain altering circuit comprises:

a capacitive element; and

a dual conversion gain element, said dual conversion gain element being controlled to connect said capacitive element to said diffusion region such that said diffusion region obtains the second conversion gain.

55. The imager of claim 54, wherein said diffusion region has a first capacitance associated with the first conversion gain, said capacitive element has a second capacitance, and a combination of the first and second capacitances is associated with the second conversion gain.

56. The imager of claim 55, wherein a register charge storing capacitance is greater than the first capacitance and less than the combination of the first and second capacitances.

57. The imager of claim 54, wherein said dual conversion gain element is a transistor having a gate connected to receive a dual conversion gain control signal.

58. The imager of claim 54, wherein said conversion gain altering circuit is controlled based on an amount of stored charge detected in said device.

59. The imager of claim 54, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said transistor is connected between said floating diffusion region and a first terminal of said capacitor, and a second terminal of said capacitor is connected to a supply voltage.

60. The imager of claim 54, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said transistor is connected between said floating diffusion region and a first terminal of said capacitor, and a second terminal of said capacitor is connected to a ground potential.

61. The imager of claim 54, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said capacitor is connected between said floating diffusion region and a first source/drain terminal of said transistor, and a second source/drain terminal of said transistor is connected to a supply voltage.

62. The imager of claim 54, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said capacitor is connected between said floating diffusion region and a first source/drain terminal of said transistor, and a second source/drain terminal of said transistor is connected to a ground potential.

63. The imager of claim 52, wherein said circuit is connected to a supply voltage.

64. The imager of claim 52, wherein said circuit is connected to a ground potential.

65. The imager of claim 52, wherein said circuit provides said diffusion region with more than two conversion gains.

66. An imager system, comprising:

a processor; and

an imaging device electrically coupled to said processor, said imaging device comprising a pixel array, at least one pixel of said array comprising;

a photosensor for accumulating stored charge,

a diffusion region, connected to receive the charge from the photosensor, said diffusion region having a first conversion gain, and

a conversion gain altering circuit connected to said diffusion region, said conversion gain altering circuit being controlled to change the first conversion gain to the second conversion gain and to change the second conversion gain to the first conversion gain.

67. The system of claim 66, wherein said photosensor has a first capacitance and said diffusion region has a second capacitance that is less than the first capacitance.

68. The system of claim 66, wherein said photosensor is a photodiode.

69. The system of claim 66, wherein said photosensor is a photodiode connected to a capacitor.

70. The system of claim 66, wherein said photosensor is a photogate.

71. The system of claim 66, wherein said photosensor is a photoconductor.

72. The system of claim 66, wherein said array is a CMOS array.

73. The system of claim 66, wherein said array is a CCD array.

74. The system of claim 66, wherein said conversion gain altering circuit comprises:

a capacitive element; and

a dual conversion gain element, said dual conversion gain element being controlled to connect said capacitive element to said diffusion region such that said diffusion region obtains the second conversion gain.

75. The system of claim 74, wherein said diffusion region has a first capacitance associated with the first conversion gain, said capacitive element has a second capacitance, and a combination of the first and second capacitances is associated with the second conversion gain.

76. The system of claim 75, wherein said photosensor has a capacitance greater than the first capacitance and less than the combination of the first and second capacitances.

77. The system of claim 74, wherein said capacitive element is a capacitor.

78. The system of claim 74, wherein said capacitive element is a polysilicon capacitor.

79. The system of claim 74, wherein said dual conversion gain element is a transistor having a gate connected to receive a dual conversion gain control signal.

80. The system of claim 74, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said transistor is connected between said floating diffusion region and a first terminal of said capacitor, and a second terminal of said capacitor is connected to a supply voltage.

81. The system of claim 74, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said transistor is connected between said floating diffusion region and a first terminal of said capacitor, and a second terminal of said capacitor is connected to a ground potential.

82. The system of claim 74, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said capacitor is connected between said floating diffusion region and a first source/drain terminal of said transistor, and a second source/drain terminal of said transistor is connected to a supply voltage.

83. The system of claim 74, wherein said dual conversion gain element is a transistor and said capacitive element is a capacitor, said capacitor is connected between said floating diffusion region and a first source/drain terminal of said transistor, and a second source/drain terminal of said transistor is connected to a ground potential.

84. The system of claim 66, wherein said circuit is connected to a supply voltage.

85. The system of claim 66, wherein said circuit is connected to a ground potential.

86. The system of claim 66, wherein said circuit provides said diffusion region with more than two conversion gains.

87. The system of claim 66, wherein the first conversion gain is used during low light conditions and the second conversion gain is used during bright light conditions.

88. The system of claim 66, further comprising sample and hold circuitry for sampling and holding a reference output and multiple pixel signal outputs from said diffusion region.

89. An imager system, comprising:

a processor; and

an imaging device electrically coupled to said processor, said imaging device comprising;

a diffusion region, connected to receive stored charge from a photosensitive device; and

a circuit connected to said diffusion region, said circuit providing said diffusion region with multiple conversion gains.

90. An imager system, comprising:

a processor; and

an imaging device electrically coupled to said processor, said imaging device comprising;

a register for inputting and outputting photo-generated charge;

a diffusion region, connected to receive the photo-generated charge from said register, said diffusion region having a first conversion gain, and

a conversion gain altering circuit connected to said diffusion region, said conversion gain altering circuit being controlled to change the first conversion gain to one of multiple conversion gains and to change said one of multiple conversion gains to said first conversion gain.

91. A method of operating an imager device, said method comprising:

storing photo-generated charge in a diffusion region;

outputting a first signal representing the stored photo-generated charge;

changing a conversion gain of the diffusion region; and

outputting a second signal representing the stored photo-generated charge in the diffusion region having the changed conversion gain.

92. The method of claim 91, wherein said changing step comprises:

changing a capacitance of the diffusion region.

93. The method of claim 91, wherein said changing step comprises:

increasing a capacitance of the diffusion region.

94. The method of claim 91 further comprising:

resetting the diffusion region to an array supply voltage prior to storing the photo-generated charge; and

outputting a third signal representing the reset diffusion region.

95. The method of claim 94 further comprising the acts of:

sampling and holding the first, second and third signals; and

using the sampled and held first, second and third signals to obtain a correlated output value.

96. The method of claim 91 further comprising:

simultaneously resetting the diffusion region and a photosensor providing the photo-generated charge prior to storing the photo-generated charge in the diffusion region; and

outputting a third signal representing the reset diffusion region.

97. The method of claim 96 further comprising the acts of:

sampling and holding the first, second and third signals; and

using the sampled and held first, second and third signals to obtain a correlated output value.

98. The method of claim 91 further comprising:

simultaneously resetting the diffusion region, a photosensor providing the photo generated charge and a capacitive region used to change the conversion gain.

99. The method of claim 98, wherein said resetting step substantially eliminates shared charges.

100. The method of claim 98, wherein said resetting step substantially eliminates lag for a subsequent readout operation.

101. A method of operating an imager device, said method comprising:

transferring photo-generated charge to a diffusion region;

determining an amount of the stored charge;

comparing the amount to a predetermined threshold;

changing a conversion gain of the diffusion region if it is determined that the amount of stored charge exceeds the threshold; and

outputting a signal indicative of the charge in the floating diffusion region.

102. The method of claim 101, wherein said changing step comprises:

changing a capacitance of the diffusion region.

103. The method of claim 101, wherein said changing step comprises:

increasing a capacitance of the diffusion region.

104. The method of claim 101 further comprising:

resetting the diffusion region to an array supply voltage prior to storing the photo-generated charge; and

outputting a third signal representing the reset diffusion region.

105. The method of claim 104 further comprising the acts of:

sampling and holding the first, second and third signals; and

using the sampled and held first, second and third signals to obtain a correlated output value.

106. The method of claim 101 further comprising:

simultaneously resetting the diffusion region and a photosensor providing the photo-generated charge prior to storing the photo-generated charge in the diffusion region; and

outputting a third signal representing the reset diffusion region.

107. The method of claim 106 further comprising the acts of:

sampling and holding the first, second and third signals; and

using the sampled and held first, second and third signals to obtain a correlated output value.

108. The method of claim 101 further comprising:

simultaneously resetting the diffusion region, a photosensor providing the photo-generated charge and a capacitive region used to change the conversion gain.

109. The method of claim 108, wherein said resetting step substantially eliminates shared charges.

110. The method of claim 108, wherein said resetting step substantially eliminates lag for a subsequent readout operation.

111. A method of operating a CMOS imager device, said method comprising:

providing a photosensor having a first capacitance;

providing a diffusion region having a second capacitance that is less than the first capacitance;

storing photo-generated charge from the photosensor in the diffusion region;

determining an amount of the stored charge;

comparing the amount to a predetermined threshold; and

adding a third capacitance to the diffusion region such that the combination of the second and third capacitances is greater than the first capacitance if it is determined that the amount of stored charge exceeds the threshold.

112. The method of claim 111, wherein said adding step changes a conversion gain of the diffusion region.

113. The method of claim 111 further comprising:

resetting the diffusion region to an array supply voltage prior to storing the photo-generated charge; and

outputting a third signal representing the reset diffusion region.

114. The method of claim 113 further comprising the acts of:

sampling and holding the first, second and third signals; and

using the sampled and held first, second and third signals to obtain a correlated output value.

115. The method of claim 111 further comprising:

simultaneously resetting the diffusion region and the photosensor prior to storing the photo-generated charge in the diffusion region; and

outputting a third signal representing the reset diffusion region.

116. The method of claim 115 further comprising the acts of:

sampling and holding the first, second and third signals; and

using the sampled and held first, second and third signals to obtain a correlated output value.

117. The method of claim 111 further comprising:

simultaneously resetting the diffusion region, the photosensor and a capacitive region used to change the conversion gain.

118. The method of claim 117, wherein said resetting step substantially eliminates shared charges.

119. The method of claim 117, wherein said resetting step substantially eliminates lag for a subsequent readout operation.

120. A method of fabricating a dual conversion gain pixel, said method comprising the steps of:

providing a substrate;

providing a photosensitive region within the substrate;

providing a floating diffusion region within said substrate, the floating diffusion region having a first capacitance; and

providing a conversion gain altering circuit within the substrate, wherein the conversion gain altering circuit is controllable to add a second capacitance to the capacitance of the diffusion region.

121. The method of claim 120 wherein said step of providing a photosensitive region within the substrate comprises providing a photodiode with a high pinning voltage within the substrate.

122. The method of claim 120 wherein said step of providing a photosensitive region within the substrate comprises:

providing a photodiode within the substrate; and

connecting the photodiode to a capacitor.

123. The method of claim 120 wherein said step of providing a photosensitive region within the substrate comprises providing a photogate within the substrate.

124. The method of claim 120 wherein said step of providing a conversion gain altering circuit comprises:

forming a capacitive element within the substrate; and

forming a transistor within the substrate, wherein the transistor is connected between the diffusion region and the capacitive element such that when the transistor is activated, a capacitance of the capacitive element is added to the first capacitance.

125. A method of fabricating a dual conversion gain pixel, said method comprising the steps of:

providing a substrate;

providing a photosensitive region within the substrate;

forming a first transistor within the substrate for resetting the pixel;

providing a floating diffusion region within said substrate, the floating diffusion region having a first capacitance;

providing a second transistor between the photosensitive region and the floating diffusion region, the second transistor being controllable to transfer charge from tie photosensitive region to the floating diffusion region;

forming a capacitive element within the substrate; and

forming a third transistor within the substrate, wherein the third transistor is connected between the diffusion region and the capacitive element such that when the third transistor is activated, a capacitance of the capacitive element is added to the first capacitance.

126. A method of fabricating a dual conversion gain pixel, said method comprising the steps of:

providing a substrate;

providing a photosensitive region within the substrate;

forming a first transistor within the substrate for resetting the pixel;

providing a floating diffusion region within said substrate, the floating diffusion region having a first capacitance and being connected to the photosensitive region;

forming a capacitive element within the substrate; and

forming a second transistor within the substrate, wherein the second transistor is connected between the diffusion region and the capacitive element such that when the second transistor is activated, a capacitance of the capacitive element is added to the first capacitance.