Optical sensor for use with output circuit that corrects a sensitivity difference between filter for high sensitivity and low sensitivity photodiodes

1. An optical sensor comprising:

a first photodiode;

a second photodiode having characteristics different from characteristics of the first photodiode;

first and second cut filters configured to block a specific wavelength range of the light;

a third photodiode configured to include the same configuration as the first photodiode, the third photodiode further configured to include the first cut filter formed on a light receiving surface of the third photodiode;

a fourth photodiode configured to include the same configuration as the second photodiode, the fourth photodiode further configured to include the second cut filter formed on a light receiving surface of the fourth photodiode; and

an output circuit including:

a first transistor having a collector connected to a cathode of the first photodiode;

a second transistor having a collector connected to an anode of the second photodiode;

a third transistor having a collector connected to a cathode of the third photodiode, the first and third transistors having a common base which is connected to the collector of the first transistor; and

a fourth transistor having a collector connected to an anode of the fourth photodiode, the second and fourth transistors having a common base which is connected to the collector of the second transistor,

wherein the output circuit is operable to calculate an equation of [(output of the first photodiode−output of the third photodiode)−(output of the second photodiode−output of the fourth photodiode)] using current values at the collector of the third transistor and at the collector of the fourth transistor, and

wherein a sensitivity of the second photodiode for the specific wavelength range is lower than a sensitivity of the first photodiode for the specific wavelength range.

2. The optical sensor of claim 1 , wherein the specific wavelength range is an UV wavelength range.

3. The optical sensor of claim 1 , wherein, when the equation of [(output of the first photodiode−output of the third photodiode)−(output of the second photodiode−output of the fourth photodiode)] is calculated, areas of the first to fourth photodiodes are adjusted in advance such that a value of current in a wavelength range other than the specific wavelength range becomes zero.

4. The optical sensor of claim 1 , wherein, when the equation of [(output of the first photodiode−output of the third photodiode)−(output of the second photodiode−output of the fourth photodiode)] is calculated, a calculation method in the output circuit is adjusted in advance such that a value of current in a wavelength range other than the specific wavelength range becomes zero.

5. The optical sensor of claim 1 , wherein each of the first and second cut filters is a multi-layered film including SiO 2 and TiO 2 .

6. An output circuit comprising:

an arithmetic circuit which is connected to a first photodiode, a second photodiode having characteristics different from characteristics of the first photodiode, first and second cut filters configured to block a specific wavelength range of the light, a third photodiode having the same configuration as the first photodiode and including the first cut filter formed on a light receiving surface of the third photodiode, and a fourth photodiode having the same configuration as the second photodiode and including the second cut filter formed on a light receiving surface of the fourth photodiode, and calculates an equation of [(output of the first photodiode−output of the third photodiode)−(output of the second photodiode−output of the fourth photodiode)];

a conversion circuit configured to convert an analog signal from the arithmetic circuit into a digital signal; and

a logic circuit which configured to subject the digital signal from the conversion circuit to a predetermined calculation process,

wherein a sensitivity of the second photodiode for the specific wavelength range is lower than a sensitivity of the first photodiode for the specific wavelength range,

wherein the arithmetic circuit includes:

a first transistor having a collector connected to a cathode of the first photodiode;

a second transistor having a collector connected to an anode of the second photodiode;

a third transistor having a collector connected to a cathode of the third photodiode, the first and third transistors having a common base which is connected to the collector of the first transistor; and

a fourth transistor having a collector connected to an anode of the fourth photodiode, the second and fourth transistors having a common base which is connected to the collector of the second transistor, and

wherein the arithmetic circuit calculates the equation of [(output of the first photodiode−output of the third photodiode)−(output of the second photodiode−output of the fourth photodiode)] using current values at the collector of the third transistor and at the collector of the fourth transistor.

7. The output circuit of claim 6 , wherein the specific wavelength range is an UV wavelength range.

8. The output circuit of claim 6 , wherein, when the equation of [(output of the first photodiode−output of the third photodiode)−(output of the second photodiode−output of the fourth photodiode)] is calculated, areas of the first to fourth photodiodes are adjusted in advance such that a value of current in a wavelength range other than the specific wavelength range becomes zero.

9. The output circuit of claim 6 , wherein, when the equation of [(output of the first photodiode−output of the third photodiode)−(output of the second photodiode−output of the fourth photodiode)] is calculated, a calculation method is adjusted in advance such that a value of current in a wavelength range other than the specific wavelength range becomes zero.

10. The output circuit of claim 6 , wherein each of the first and second cut filters is a multi-layered film including SiO 2 and TiO 2 .