Display apparatus

1. A display apparatus comprising:

an image display unit having a plurality of arrayed pixel circuits; and

an image signal compensation circuit coupled to the image display unit, wherein:

each of the pixel circuits includes:

a current light emitting device;

a driving transistor supplying a current to the current light emitting device; and

a compensating capacitor which is disposed between a gate and a source of the driving transistor, and compensates a threshold voltage of the driving transistor,

the image signal compensation circuit includes:

a compensation memory storing compensation data for compensating mobility dispersion among driving transistors of the plurality of arrayed pixel circuits, the compensation data being for all of the plurality of arrayed pixel, the compensation memory being configured by a frame memory;

a comparison circuit which compares an image signal with a threshold value of luminance; and

an arithmetic circuit which outputs a compensated image signal being compensated by using the compensation data read from the compensation memory,

the comparison circuit outputs an enabling signal to the compensation memory and the arithmetic circuit when the image signal has a luminance larger than the threshold value,

the compensation data is output from the compensation memory to the arithmetic circuit according to the enabling signal, and

the image signal compensation circuit outputs the compensated image signal to the image display unit when the image signal has the luminance larger than the threshold value, and outputs the image signal to the image display unit when the image signal has a luminance smaller than the threshold value.

2. The display apparatus of claim 1 , wherein:

the compensation memory stores compensation data for compensating variation of current in the driving transistors,

the image signal compensation circuit further comprises

a lighting ratio calculation circuit calculating a lighting ratio of the plurality of arrayed pixel circuits for every frame of the image signal,

the comparison circuit comprises:

a first comparison circuit comparing the image signal and a first threshold of luminance; and

a second comparison circuit comparing the lighting ratio calculated by the lighting ratio calculation circuit and a second threshold which is different from the first threshold,

wherein the image signal compensation circuit compensates the image signal when the image signal is larger than the first threshold and the lighting ratio is larger than the second threshold.

3. The display apparatus of claim 1 , wherein:

each of the pixel circuits further comprises:

a first capacitor having a first terminal connected to a gate of the driving transistor;

a second capacitor connected between a second terminal of the first capacitor and a source of the driving transistor;

a first switch applying a reference voltage to a node to which the first and the second capacitors are connected;

a second switch supplying an image signal voltage to the gate of the driving transistor;

a third switch supplying an initialization voltage to drain of the driving transistor; and

a fourth switch supplying current to the drain of the driving transistor for emitting light from the current light emitting device, and

the second capacitor is the compensating capacitor.

4. The display apparatus of claim 1 , wherein the comparison circuit further comprises a logic AND circuit for receiving output signals from the first comparison circuit and the second comparison circuit.

5. The display apparatus of claim 4 , wherein:

the logic AND circuit outputs an enabling signal to the compensation memory and the arithmetic circuit, and

the compensation data is output from the compensation memory to the arithmetic circuit according to the enabling signal.

6. The display apparatus of claim 1 , wherein each of the compensation data for a given driving transistor is calculated from a ratio between a mobility of the given driving transistor and a mobility of a standard driving transistor.