THERMAL INFRARED SOLID STATE IMAGING DEVICE AND INFRARED CAMERA

• US 20080251721A1
• Filed: 04/04/2008
• Published: 10/16/2008
• Est. Priority Date: 04/05/2007
• Status: Active Grant

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Electric Corporation
• Inventors: UENO, Masashi
• Granted Patent: US 7,718,966 B2
• Time in Patent Office: Days
• US Class Current: 250/332
• CPC Class Codes: G01J 5/08 Optical arrangements
• CPC Class Codes: G01J 5/0853 having infrared absorbers other than the usual absorber layers deposited on infrared detectors like bolometers, wherein the heat propagation between the absorber and the detecting element occurs within a solid
• CPC Class Codes: G01J 5/20 using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

An infrared solid state imaging device includes a pixel area with arranged infrared detection pixels and a integration circuit for modulating output current based on the output of the pixel. The integration circuit contains an integrating transistor that modulates a current based on the difference in potential between first and second constant current devices, a integration capacitor for storing the modulated current and being reset periodically, a bias current supply transistor, a switch for connecting the drain with the gate of the bias current supply transistor, a capacitor providing AC coupling between the output of the integrating transistor and the integrating capacitor, a gate bias switch for providing the integrating transistor with a bias voltage, a switch for selecting, as input to the integrating transistor, either one of outputs from the first and second constant current devices, and a capacitor for providing AC coupling between the switch and the gate of the integrating transistor.

Claims

1. A thermal infrared solid state imaging device comprising:

a pixel area having a two-dimensional array of infrared detection pixels, the infrared detection pixel including at least one or more serially connected temperature detection devices having a heat insulation structure and an infrared absorption structure;

a plurality of drive lines, each drive line connecting the anodes of the pixels in common by row;

a plurality of signal lines, each signal line connecting the cathodes of the pixels in common by column and connected to a first constant current device at the end of each column;

a vertical scanning circuit that sequentially selects the drive line and connects the selected drive line to a power supply;

a second constant current device that is disposed to each signal line near the first constant current device, and supplies a current substantially equal to a current by the first constant current device;

an integration circuit that outputs a current modulated by the difference in potential between the first constant current device and the second constant current device;

a sample-and-hold circuit that samples and holds the output of the integration circuit; and

a horizontal scanning circuit that selects the output of the sample-and-hold circuit by column,

wherein the integration circuit includes

an integrating transistor that modulates the output current based on the difference in potential between the first constant current device and the second constant current device,

an integrating capacitor that stores the modulated current and is periodically reset to a reference voltage,

a bias current supply transistor that has a gate connected to a holding capacitor and is connected in series to the integrating transistor,

a gate connection switch that connects and disconnects a node between the bias current supply transistor and the integrating transistor with the gate of the bias current supply transistor,

an output coupling capacitor that provides AC coupling between the node and the integrating capacitor,

a gate bias switch that is connected to the gate of the integrating transistor and can supply a bias voltage,

an input selector switch that is connected to the gate of the integrating transistor, and selects, as input to the integration circuit, either one of the potential of the first constant current device and the potential of the second constant current device, and

an input coupling capacitor that provides AC coupling between the input selector switch and the gate of the integrating transistor.

2. The thermal infrared solid state imaging device according to claim 1, wherein:

during a reset period of the integrating capacitor, the input selector switch is connected to the potential of the second constant current device, and the gate connection switch and gate bias switch are closed; and

during an integration period of the integrating capacitor, the input selector switch is connected to the potential of the first constant current device, and the gate connection switch and the gate bias switch are open.

3. The thermal infrared solid state imaging device according to claim 2, wherein

the reset period of the integrating capacitor is set in a horizontal blanking period, and substantially all of the remaining horizontal scanning period is set as the integration period;

and

the timing at which the gate bias switch opens is set before the timing at which the gate connection switch opens.

4. The thermal infrared solid state imaging device according to claim 1, further comprising:

a bias line that commonly connects the input nodes of the second constant current device in parallel to the drive line, and has resistance substantially equal to the drive line;

a reference pixel that is disposed outside the pixel area and is structurally identical to the infrared detection pixel except for not having a heat insulation structure and/or infrared absorption structure;

a third constant current device that is connected to the reference pixel and supplies a current equal to a current from the first constant current device; and

a buffer amplifier and low-pass filter connected between the output of the reference pixel output and the bias line.

5. The thermal infrared solid state imaging device according to claim 1, further comprising:

a bias line that commonly connects the input nodes of the second constant current devices in parallel to the drive line, and has resistance substantially equal to the drive line;

a reference pixel that is disposed inside the pixel area and is structurally identical to the infrared detection pixel except for not having a heat insulation structure and/or infrared absorption structure;

a second sample-and-hold circuit that samples and holds the output of a device relating to the reference pixel; and

a bias generating circuit that generates a bias voltage according to the difference between the output of the second sample-and-hold circuit and a reference voltage to apply the bias voltage to the bias line.

6. The thermal infrared solid state imaging device according to claim 1, further comprising:

a bias line that commonly connects the input nodes of the second constant current device in parallel to the drive line, and has resistance substantially equal to the drive line;

a bias generating circuit that generates a bias voltage according to the difference between a reference voltage and the average output of all or part of the devices in the pixel area, to apply the bias voltage to the bias line.

7. The thermal infrared solid state imaging device according to claim 1, wherein the temperature detection device is a PN junction diode or a resistance bolometer.

11. An infrared camera comprising:

a thermal infrared solid state imaging device according to claim 1;

an optical system for focusing an infrared image on the thermal infrared solid state imaging device; and

an amplifier circuit for amplifying and outputting an image signal output from the thermal infrared solid state imaging device.

8. A thermal infrared solid state imaging device comprising:

a pixel area having a one-dimensional or two-dimensional array of infrared detection pixels having a heat insulation structure and infrared absorption structure;

a reference pixel that is structurally identical to the infrared detection pixels except for not having a heat insulation structure and/or infrared absorption structure;

integration circuits each of which modulates a current of an integrating transistor according to difference in output of the infrared detection pixel and the reference pixel, and stores the modulated current in an integrating capacitor that is periodically reset to a reference voltage;

sample-and-hold circuits each of which samples and holds the output of the corresponding integration circuit; and

a horizontal scanning circuit that selects the output of the sample-and-hold circuit by column;

wherein the integration circuit includes

an integrating transistor that modulates the output current based on the difference in potential between the first constant current device and the second constant current device,

an integrating capacitor that stores the modulated current and is periodically reset to a reference voltage,

a bias current supply transistor that has a gate connected to a holding capacitor and is connected in series to the integrating transistor,

a gate connection switch that connects and disconnects a node between the bias current supply transistor and the integrating transistor with the gate of the bias current supply transistor,

an output coupling capacitor that provides AC coupling between the node and the integrating capacitor,

a gate bias switch that is connected to the gate of the integrating transistor and can supply a bias voltage,

an input selector switch that is connected to the gate of the integrating transistor, and selects, as input to the integration circuit, either one of the potential of the first constant current device and the potential of the second constant current device, and

an input coupling capacitor that provides AC coupling between the input selector switch and the gate of the integrating transistor.

9. The thermal infrared solid state imaging device according to claim 8, wherein

during a reset period of the integrating capacitor, the input selector switch is connected to the potential of the second constant current device, and the gate connection switch and gate bias switch are closed;

and

during an integration period of the integrating capacitor, the input selector switch is connected to the potential of the first constant current device, and the gate connection switch and the gate bias switch are open.

10. The thermal infrared solid state imaging device according to claim 9, wherein

the reset period of the integrating capacitor is set in a horizontal blanking period, and substantially all of the remaining horizontal scanning period is set as the integration period;

and

the timing at which the gate bias switch opens is set before the timing at which the gate connection switch opens.

12. An infrared camera comprising:

a thermal infrared solid state imaging device according to claim 8;

an optical system for focusing an infrared image on the thermal infrared solid state imaging device; and

an amplifier circuit for amplifying and outputting an image signal output from the thermal infrared solid state imaging device.