Signal processing device and signal processing method

1. A signal processing device comprising:

an integrator configured to integrate an electrical charge corresponding to electromagnetic waves;

a first analog-to-digital converter configured to perform an analog-to-digital conversion operation that generates digital data of the electrical charge using an integration output from the integrator, on a parallel with an integration operation performed by the integrator; and

a histogram creator configured to create a histogram that represents an energy distribution of the electromagnetic waves, from the digital data generated by the first analog-to-digital converter.

2. The device according to claim 1 , further comprising an integration period setting unit configured to, with respect to the integrator, set a period of integration of the electrical charge, wherein

the integrator includes

an integrating capacitor configured to store therein the electrical charge, and

a discharging circuit configured to discharge the integrating capacitor, and

the first analog-to-digital converter includes

a comparator configured to compare the integration output and a predetermined threshold value, and

a counter configured to output, as digital data of the electrical charge, the number of times for which a value of the integration output becomes equal to or greater than the predetermined threshold value, and

the first analog-to-digital converter is configured to, during the period of integration, while a value of the integration value is equal to or greater than the predetermined threshold value, supply a comparison output of the comparator to the discharging circuit and discharge the integrating capacitor.

3. The device according to claim 2 , further comprising:

an output controller configured to, at the end of the integration period, output the integration output having a lower value than the predetermined threshold value; and

a second analog-to-digital converter configured to generate digital data of the integration output having a lower value than the predetermined threshold value, wherein

the histogram creator is configured to create a histogram representing an energy distribution of the electromagnetic waves from the digital data generated by the first analog-to-digital converter and the digital data generated by the second analog-to-digital converter.

4. The device according to claim 2 , wherein

the integrator includes at least two integrating capacitors configured to store the electrical charge, and at least two discharging circuits configured to store electrical charge in the integrating capacitors and discharge the integrating capacitors,

the signal processing device further comprises a discharge controller configured to connect the integrating capacitors in a discharged state to the integrator during the period of integration in a way that control of the discharging circuits is performed so as to switch the integrating capacitors in an electrical charge storing state to the discharged state and to switch the integrating capacitors in the discharged state to the electrical charge storing state every time the comparison output of the comparator becomes equal to or greater than the predetermined threshold value.

5. The device according to claim 2 , wherein

the integrator includes an integrating capacitor configured to store a positive electrical charge and an integrating capacitor configured to store a negative electrical charge,

the device further comprises

a differential converter unit configured to generate, from the electrical charge corresponding to electromagnetic waves, a positive electrical charge and a negative electrical charge having mutually different polarities, and supply the positive electrical charge and the negative electrical charge to the integrator;

a capacitor having a substantially same capacity as the integrating capacitors and configured to store a positive electrical charge and a negative electrical charge; and

an electrical charge cancellation circuit configured to cancel out the electrical charge supplied to the integrator during the period of integration in a way that the negative electrical charge stored in the capacitor is supplied to a line for supplying a positive electrical charge from the differential converter unit to the integrator and the positive electrical charge stored in the capacitor is supplied to a line for supplying a negative electrical charge from the differential converter unit to the integrator every time the comparison output of the comparator becomes equal to or greater than the predetermined threshold value.

6. The device according to claim 2 , wherein

the comparator is set with at least a first threshold value and a second threshold value that are different from each other, and

the comparator is configured to perform a comparison operation in which the first threshold value is compared with the integration output and, after a value of the integration output becomes equal to or greater than the first threshold value, the second threshold value is compared with the integration output.

7. A signal processing method comprising:

performing an analog-to-digital conversion operation that generates digital data of an electrical charge using an integration output from an integrator configured to integrate the electrical charge corresponding to electromagnetic waves, on a parallel with an integration operation performed by the integrator; and

creating a histogram that represents an energy distribution of the electromagnetic waves, from the generated digital data.