Color display device with pixel circuits including two capacitors
In a pixel circuit ( 10 ), TFTs ( 12 ) to ( 16 ) are connected and driven such that a threshold voltage Vth of a TFT ( 11 ), which is a drive transistor, can be held in a threshold holding capacitor ( 19 ) having a capacitance value c 1 , voltages, including a data potential Vdata representing an image to be displayed, can be held in a data holding capacitor ( 18 ) having a capacitance value c 2 , and charges in the data holding capacitor ( 18 ) and the threshold holding capacitor ( 19 ) are redistributed at the time of light emission. As a result, a potential obtained by multiplying the data potential Vdata by c 1 /(c 1 +c 2 ) is provided to a gate potential of the TFT ( 11 ).
1. An active-matrix color display device comprising:
a plurality of video signal lines configured to transmit signals representing an image to be displayed;
a plurality of scanning signal lines and control lines crossing the video signal lines;
pixel circuits arranged in a matrix corresponding to respective intersections of the video signal lines and the scanning signal lines, each pixel circuit configured to display a pixel in one of a plurality of primary colors for forming the image to be displayed;
a plurality of power lines configured to supply a power-supply voltage to the pixel circuits;
a scanning signal line driver circuit configured to selectively or collectively drive the scanning signal lines and the control lines;
a video signal line driver circuit configured to drive the video signal lines by applying the signals representing the image to be displayed; and
a power control circuit configured to drive the power lines, wherein,
the pixel circuit includes:
an electro-optic element configured to be driven by a current provided by the power line being supplied with the power-supply voltage;
a drive transistor provided in a path of the current flowing through the electro-optic element, the transistor configured to determine the current to be flowed through the path;
a data holding capacitor connected at one terminal to a control terminal of the drive transistor and at the other terminal to the power line or a connecting point provided with a predetermined voltage;
a write control transistor connected to the data holding capacitor such that a voltage is provided to the data holding capacitor when the write control transistor is on after an initialization operation and in a writing operation before a light emission period, and the provided voltage is held in the data holding capacitor when the write control transistor is off, the provided voltage having a value changed by a predetermined value from a voltage obtained by adding or subtracting a voltage corresponding to a video signal representing an image to be displayed to or from a threshold voltage of the drive transistor; and
a threshold holding capacitor connected at one terminal to the control terminal of the drive transistor and at the other terminal to a conductive terminal of the drive transistor or a connecting point provided with a predetermined constant voltage,
the write control transistor connected to the data holding capacitor such that a voltage is provided to the threshold holding capacitor when the write control transistor is on after the initialization operation and in the writing operation before the light emission period, and the provided voltage is held in the threshold holding capacitor when the write control transistor is off, the provided voltage being the threshold voltage or having a value changed by a predetermined value from the threshold voltage,
the pixel circuits include a first pixel circuit configured to display a first primary color, a second pixel circuit configured to display a second primary color, and a third pixel circuit configured to display a third primary color, and
among the first to third pixel circuits, as a service life of the electro-optic element becomes shorter, combined capacitance of the data holding capacitor and the threshold holding capacitor increases and a layout area of the electro-optic element increases.
2. The color display device according to claim 1 , wherein the first primary color is blue, the second primary color is green, and the third primary color is red.
3. The color display device according to claim 1 , wherein,
the first primary color is red, the second primary color is green, and the third primary color is blue,
the pixel circuits include a fourth pixel circuit configured to display a fourth primary color, the fourth primary color being white, and
a capacitance ratio d of the threshold holding capacitor to the data holding capacitor in the fourth pixel circuit is lower than a capacitance ratio a of the threshold holding capacitor to the data holding capacitor in the first pixel circuit.
4. The color display device according to claim 1 , wherein,
the first primary color is red, the second primary color is green, and the third primary color is blue,
the pixel circuits include a fourth pixel circuit configured to display a fourth primary color, the fourth primary color being yellow, and
a capacitance ratio d of the threshold holding capacitor to the data holding capacitor in the fourth pixel circuit is higher than a capacitance ratio a of the threshold holding capacitor to the data holding capacitor in the first pixel circuit.