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

• US 20060077169A1
• Filed: 08/08/2005
• Published: 04/13/2006
• Est. Priority Date: 10/12/2004
• Status: Active Grant

• Current Assignee: 138 East LCD Advancements Limited (Vector Capital Corporation)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Fujikawa, Shinsuke
• Granted Patent: US 7,948,483 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

A photo detection circuit includes 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 with a predetermined period. A voltage signal of the connection point is extracted as an output signal.

Claims

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 with a predetermined period,

wherein a voltage signal of the connection point is extracted as an output signal.

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 having a period shorter than the on/off period 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.

11. An electronic apparatus comprising the electro-optical device according to claim 5.

9. An electro-optical device comprising:

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;

a control circuit that generates a plurality of control signals;

a driving circuit that generates a driving signal based on the plurality of control signals to output the driving signal to at least one of the plurality of data lines and the plurality of scanning lines; and

a photo detection circuit which includes 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 and switching on and off based on a first signal, the photo detection circuit extracting a voltage signal from the connection point,

wherein the first signal serves as any one of the plurality of control signals.

10. An electro-optical device comprising:

a plurality of data lines;

a plurality of scanning lines;

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

a control circuit that generates a plurality of control signals;

a driving circuit that generates a driving signal based on the plurality of control signals to output the driving signal to at least one of the plurality of data lines and the plurality of scanning lines; and

a photo detection circuit which includes 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, a switching element provided between the connection point and the low-potential-side power supply and switching on and off based on a first signal, and a logic circuit that executes logical multiplication between the first signal and a second signal having a period shorter than a period of the first signal to output a binarization signal,

wherein the first and second signals serve as a portion of the plurality of control signals.

12. A method of controlling a photo detection circuit which includes a photodiode whose cathode is connected to a high-potential-side power supply and whose anode is connected to a connection point, and a capacitor element provided between the connection point and a low-potential-side power supply, the method comprising:

short-circuiting both terminals of the capacitor element with a predetermined period;

executing logical multiplication between a reference signal having a period shorter than the predetermined period, and a voltage signal of the connection point to generate a binarization signal; and

outputting the binarization signal as a luminance signal indicating luminance.