Compensation of threshold voltage in driving transistor of organic light emitting diode display device

An organic light emitting diode display device comprising a plurality of pixels arranged in a matrix form, each of the pixels comprising:

• a driving thin film transistor (TFT) including a gate electrode coupled to a first node, a source electrode coupled to a second node, and a drain electrode coupled to a high-potential voltage line;
• an organic light emitting diode between the second node and a low-potential voltage line;
• a first TFT configured to connect a data line to the first node during a data voltage supply period of a frame period;
• an initialization control circuit coupled between the first node and a first reference voltage line supplying a first reference voltage, the initialization control circuit further connected to a second node, a third node and a second reference voltage line supplying a second reference voltage, the initialization control circuit configured to initialize the first node to the first reference voltage, and the second and third nodes to a second reference voltage during an initialization period of the frame period preceding the data voltage supply period, the initialization control circuit comprising:
• a second TFT including a gate electrode coupled to an emission line, a source electrode coupled to the third node, and a drain electrode coupled to the second node,
• a third TFT including a gate electrode coupled to an initialization line for carrying an initialization signal to indicate the initialization period, a source electrode coupled to the first reference voltage line supplying the first reference voltage, and a drain electrode coupled to the first node, and
• a fourth TFT including a gate electrode coupled to the initialization line, a source electrode coupled to the second reference voltage line supplying the second reference voltage, and a drain electrode coupled to the third node;
• and
• a first capacitor coupled between the first node and the third node, the first capacitor configured to store a voltage difference between the first node and the third node during the initialization period, and change a voltage level of the first node based on a voltage level of the third node in a threshold voltage sensing period between the initialization period and the data voltage supply period.