Readout integrated circuit for infrared signal and method of reading out infrared signal

1. A readout integrated circuit for an infrared signal, the readout integrated circuit comprising:

a skimming transistor configured to allow a background current to flow through a microbolometer according to a gate voltage;

a plurality of global lines each configured to supply a voltage of a different level;

a global line selecting unit configured to select a global line to be connected to the skimming transistor; and

a signal detecting unit configured to output a digital signal corresponding to a signal current flowing through the microbolometer.

2. The readout integrated circuit of claim 1 , wherein the global line selecting unit comprises:

an analog-to-digital converter configured to convert a voltage corresponding to the background current flowing through the skimming transistor in a calibration mode to digital data;

a first memory configured to store the digital data;

a decoder configured to decode the digital data stored in the first memory and output a decoded signal in an operation mode; and

a switch part configured to select a global line from among the plurality of global lines according to the decoded signal to connect the selected global line to a gate of the skimming transistor.

3. The readout integrated circuit of claim 2 , wherein the global line selecting unit further comprises a plurality of switches configured to allow the skimming transistor to perform a diode connected operation in the calibration mode and to end the diode connected operation in the operation mode.

4. The readout integrated circuit of claim 1 , wherein the signal detecting unit comprises:

an integration capacitor configured to supply the signal current flowing through the microbolometer;

a comparator configured to compare a voltage corresponding to the signal current with a reference voltage and output a comparison result;

a refresh transistor configured to control charging of the integration capacitor to have a voltage corresponding to an output of the comparator;

a counter configured to count the output of the comparator; and

a second memory configured to store an output of the counter.

5. A method of detecting an infrared signal, the method comprising:

storing, during a calibration mode, first digital data corresponding to a voltage corresponding to a background current flowing through a microbolometer;

selecting, during operation mode, a voltage corresponding to the first digital data; and

producing, during operation mode, second digital data corresponding to a signal current, wherein the background current and the signal current flow through the microbolometer.

6. The method of claim 5 , wherein the operating of the calibration mode comprises:

performing, by a skimming transistor connected to the microbolometer, a diode connected operation;

producing the first digital data corresponding to the background current flowing through the microbolometer; and

storing the first digital data.

7. The method of claim 5 , wherein the selecting of the global line comprises:

reading out the first digital data; and

decoding the read-out first digital data to select a global line from among a plurality of global lines.

8. The method of claim 5 , wherein the producing of the second digital data comprises:

comparing a voltage corresponding to the signal current with a predetermined reference voltage and outputting a comparison result;

counting the comparison result; and

storing the counted data.

9. The method of claim 8 , wherein the outputting of the comparison result refreshes the signal current voltage to allow further comparison with the predetermined reference voltage.

10. The method of claim 5 , wherein the voltage corresponding to the first digital data is selected from among a plurality of global lines each providing a voltage of a different level.

11. The method of claim 5 , wherein the signal current changes as temperature of an object to be imaged changes.