Photo detection circuit, method of controlling the same, electro-optical panel, electro-optical device, and electronic apparatus

1. A photo detection circuit comprising:

a photodiode whose cathode is connected to a high-potential-side power supply and whose anode is connected to a connection point;

a capacitor element provided between the connection point and a low-potential-side power supply; and

a switching element, provided between the connection point and the low-potential-side power supply, that switches on and off based on a repeating reset pulse signal, the repeating reset pulse signal repeating with a first predetermined frequency, and

an output circuit converting a voltage signal of the connection point into a plurality of pulse signals having a second predetermined frequency and outputting the plurality of pulse signals only while the voltage signal of the connection point is substantially equal to a voltage of the high-potential-side power supply and until the switching element is turned on,

the switching on and off of the switching element corresponding with the repeating reset pulse signal supplied to the photo detection circuit, the repeating reset pulse signal having a pulse width equal to one full cycle of one pulse signal of the plurality of pulse signals that includes a high pulse and an adjacent low pulse.

2. The photo detection circuit according to claim 1 , further comprising:

a voltage-to-frequency converting circuit that converts the voltage signal into a frequency signal,

wherein the frequency signal is output instead of the voltage signal as the output signal.

3. The photo detection circuit according to claim 2 ,

wherein the voltage-to-frequency converting circuit has a logic circuit that executes logical multiplication between the voltage signal and a reference signal, the voltage-to-frequency converting circuit having a frequency greater than the on/off frequency of the switching element to output a binarization signal, and

the binarization signal is output as the frequency signal.

4. The photo detection circuit according to claim 3 , further comprising:

a counting unit that counts the binarization signal to output a count data signal indicating a result of counts per unit time,

wherein the count data signal is output as the output signal.

5. An electro-optical panel comprising:

the photo detection circuit according to claim 1 ;

a plurality of data lines;

a plurality of scanning lines;

a plurality of pixel circuits provided to correspond to intersections of the data lines and the scanning lines, and each having an electro-optical element having an optical characteristic changed by an electrical effect; and

a driving circuit that outputs a signal to at least one of the plurality of data lines and the plurality of scanning lines to drive the electro-optical element.

6. An electro-optical device comprising:

an electro-optical panel according to claim 5 ;

a light source that radiates light from one surface of the electro-optical panel toward the other surface; and

a dimmer circuit that adjusts an amount of light emitted from the light source based on the output signal of the photo detection circuit,

wherein the electro-optical element is a liquid crystal element whose transmittance is changed according to an applied voltage.

7. An electro-optical device comprising:

the electro-optical panel according to claim 5 ; and

an image processing circuit that outputs an image signal whose level is adjusted based on the output signal of the photo detection circuit,

wherein the electro-optical element is composed of a light-emitting element that emits light with a luminance according to a driving current, and

the driving circuit controls the driving current based on the image signal output from the image processing circuit.

8. An electro-optical device comprising:

an electro-optical panel according to claim 5 ; and

a power supply circuit that outputs a power supply voltage whose level is adjusted based on the output signal of the photo detection circuit,

wherein the driving circuit outputs to the data line a data signal according to a gray-scale level to be displayed,

the electro-optical element is composed of a light-emitting element for emitting light with a luminance according to a driving current,

the pixel circuit has a driving transistor for supplying the driving current to the light-emitting element, and

the driving transistor supplies to the light-emitting element a driving current having a level based on the power supply voltage and the data signal.

9. An electronic apparatus comprising the electro-optical panel according to claim 5 .

10. The photo detection circuit according to claim 1 , wherein each of the photodiode, capacitor element and switching element are directly connected to the connection point.