Organic light emitting display device, and method of generating a gamma reference voltage for the same

An organic light emitting display device, comprising:

• a display panel having a plurality of pixel circuits;
• a scan driving unit configured to provide a scan signal to the pixel circuits via a plurality of scan lines;
• a data driving unit configured to provide a data signal to the pixel circuits via a plurality of data lines;
• a power unit configured to provide a first power voltage and a second power voltage to the pixel circuits, the first power voltage being greater than the second power voltage;
• a gamma reference voltage generating unit configured to generate a gamma reference voltage corresponding to a voltage difference between the first power voltage and a subtraction reference voltage;
• a gamma voltage generating unit configured to generate a plurality of gamma voltages based on the gamma reference voltage, and to provide the gamma voltages to the data driving unit;
• and
• a timing control unit configured to control at least one of the scan driving unit, the data driving unit, the power unit, the gamma reference voltage generating unit, and the gamma voltage generating unit.