Infrared imaging element detecting temperature change, and infrared camera using the same element
An infrared imaging element includes a photosensitive pixel array and a driving line for each photosensitive pixel. The infrared imaging element includes a vertical scanning circuit, a signal line, a bias line, a differential integration circuit that time-integrates a difference between a voltage across the first constant current source and a voltage across the second constant current source; a horizontal scanning circuit; a reference pixel array that outputs a reference signal changing in accordance with a change in a temperature of photosensitive pixels; a bias generating circuit that generates a bias voltage for applying the bias voltage to the bias line, the bias voltage corresponding to a difference between a reference voltage and a differential signal between the reference signal and a voltage on the bias line; and a voltage generating circuit that generates a temperature signal generation voltage based on the bias voltage.
1. An infrared imaging element comprising:
a photosensitive pixel array having a heat insulating layer and an infrared ray absorption member, the photosensitive pixel array including a plurality of photosensitive pixels arranged in a two-dimensional shape;
a driving line commonly connected with one pole of each of the photosensitive pixels for each of rows;
a vertical scanning circuit that sequentially selects the driving line to connect the driving line to a power supply;
a signal line commonly connected with another pole of each of the photosensitive pixels for each of columns, the signal line having an end part connected with first constant current source;
a bias line that is connected in parallel with second constant current source provided for each of the columns of the photosensitive pixel array, the bias line generating a voltage drop substantially identical to that of the driving line;
a differential integration circuit provided for each of the columns of the photosensitive pixel array, the differential integration circuit time-integrating and outputting a difference between a voltage across the first constant current source and a voltage across the second constant current source with a predetermined integration time; and
a horizontal scanning circuit that selects an output signal of the differential integration circuit for each of the columns to guide the output signal to an image signal output terminal as an image signal,
wherein the infrared imaging element further comprises:
a reference pixel array that outputs a reference signal that changes substantially in accordance with a change in a temperature of a whole of the plurality of photosensitive pixels;
a bias generating circuit that generates a bias voltage for applying the bias voltage to the bias line, the bias voltage corresponding to a difference between a predetermined reference voltage and a differential signal between the reference signal and a voltage at a predetermined position on the bias line, and the bias voltage including a voltage component of an output level stabilized voltage; and
a voltage generating circuit that generates a predetermined temperature signal generation voltage based on the bias voltage, and adds the predetermined temperature signal generation voltage to the image signal output terminal,
wherein the temperature signal generation voltage is adjusted to become a predetermined voltage together with a voltage level of the image signal, and is configured to be added to the image signal at a timing different from that of the image signal.
2. The infrared imaging element as claimed in claim 1 ,
wherein the voltage generating circuit generates the temperature signal generation voltage based on the bias voltage and an input voltage from a power supply terminal, and adds the temperature signal generation voltage to the image signal output terminal, and
wherein the voltage generating circuit also generates an output level stabilized voltage, and applies the output level stabilized voltage to the bias line.
3. The infrared imaging element as claimed in claim 2 ,
wherein the output level stabilized voltage includes a noise component synchronized with a driving power supply voltage that drives the photosensitive pixels.
4. The infrared imaging element as claimed in claim 2 ,
wherein a circuit gain of the output level stabilized voltage with respect to an input voltage in the voltage generating circuit is set to be more than 0 and 1 or less.
5. The infrared imaging element as claimed in claim 2 , further comprising a low-pass filter that low-pass filters the bias voltage, and outputs the bias voltage to the voltage generating circuit.
6. The infrared imaging element as claimed in claim 1 ,
wherein the reference pixel array is formed to remove either one or both of the heat insulating layer and the infrared ray absorption member, or is configured to have an infrared ray shielding layer.
7. The infrared imaging element as claimed in claim 1 ,
wherein the photosensitive pixel array is formed to remove either one or both of the heat insulating layer and the infrared ray absorption member.
8. The infrared imaging element as claimed in claim 1 ,
wherein the reference pixel array is formed to be adjacent to at least one side in a vertical direction or a horizontal direction of the photosensitive pixel array.
9. The infrared imaging element as claimed in claim 1 ,
wherein the reference pixel array includes a plurality of reference pixels, and
wherein the infrared imaging element further comprises a sample-and-hold circuit that is provided in a preceding stage of the bias generating circuit, samples and holds pixel signals from the plurality of reference pixels after averaging the pixel signals, and outputs sampled and held pixel signals to the bias generating circuit.
10. The infrared imaging element as claimed in claim 1 ,
wherein the first constant current source and the second constant current source are provided to sandwich the photosensitive pixel array.
11. The infrared imaging element as claimed in claim 1 ,
wherein the voltage generating circuit is configured to be driven during an integration interval of the differential integration circuit.
12. An infrared camera comprising:
an infrared imaging element; and
an image correction circuit that corrects an output image signal to be constant based on an image signal, the image signal being outputted from the infrared imaging element and including the temperature signal generation voltage,
wherein the infrared imaging element comprises:
a photosensitive pixel array having a heat insulating layer and an infrared ray absorption member, the photosensitive pixel array including a plurality of photosensitive pixels arranged in a two-dimensional shape;
a driving line commonly connected with one pole of each of the photosensitive pixels for each of rows;
a vertical scanning circuit that sequentially selects the driving line to connect the driving line to a power supply;
a signal line commonly connected with another pole of each of the photosensitive pixels for each of columns, the signal line having an end part connected with first constant current source;
a bias line that is connected in parallel with second constant current source provided for each of the columns of the photosensitive pixel array, the bias line generating a voltage drop substantially identical to that of the driving line;
a differential integration circuit provided for each of the columns of the photosensitive pixel array, the differential integration circuit time-integrating and outputting a difference between a voltage across the first constant current source and a voltage across the second constant current source with a predetermined integration time; and
a horizontal scanning circuit that selects an output signal of the differential integration circuit for each of the columns to guide the output signal to an image signal output terminal as an image signal, and
wherein the infrared imaging element further comprises:
a reference pixel array that outputs a reference signal changing substantially in accordance with a change in a temperature of a whole of the plurality of photosensitive pixels;
a bias generating circuit that generates a bias voltage for applying the bias voltage to the bias line, the bias voltage corresponding to a difference between a predetermined reference voltage and a differential signal between the reference signal and a voltage at a predetermined position on the bias line, and the bias voltage including a voltage component of an output level stabilized voltage; and
a voltage generating circuit that generates a predetermined temperature signal generation voltage based on the bias voltage, and adds the predetermined temperature signal generation voltage to the image signal output terminal,
wherein the temperature signal generation voltage is adjusted to become a predetermined voltage together with a voltage level of the image signal, and is configured to be added to the image signal at a timing different from that of the image signal.