Pixel circuit, electro-optical device, and electronic apparatus
To accurately display a predetermined gray level. A first transistor T 1 and a second transistor T 2 are arranged in a first path 501 from a power line 41 to a constant-current circuit 301 . A driving transistor Tdr and a current supply transistor Tc are arranged in a second path 502 from the power line 41 to an OLED element 51 . A capacitor C 1 connected to the gate of the driving transistor and a capacitor C 2 connected to the gate of the current supply transistor Tc hold a voltage corresponding to a data current Idata-j flowing in the first path 501 . The driving transistor Tdr controls a driving current flowing in the second path 502 in accordance with the voltage held in the capacitor C 1 . The current supply transistor Tc controls the driving current flowing in the second path 502 in accordance with the voltage held in the capacitor C 2.
1. A pixel circuit comprising:
a first path from a power supply to a current source;
a second path from the power supply to an electro-optical element;
a first transistor arranged in the first path:
a third transistor for diode-connecting the first transistor:
a first voltage holding element for holding a voltage corresponding to a data current flowing in the first path;
a driving transistor for controlling a driving current flowing in the second path in accordance with the voltage held in the first voltage holding element connected to a gate of the driving transistor, the driving transistor being arranged in the second path, the gate of the driving transistor also being connected to a gate of the first transistor;
a second transistor arranged in the first path;
a fourth transistor for diode-connecting the second transistor;
a second voltage holding element for holding a voltage corresponding to the data current flowing in the first path; and
a current supply transistor for controlling the driving current flowing in the second path in accordance with the voltage held in the second voltage holding element connected to a gate of the current supply transistor, the current supply transistor being arranged in the second path, the gate of the current supply transistor also being connected to a gate of the second transistor,
the first transistor and the driving transistor constituting a first current mirror circuit, the second transistor and the current supply transistor constituting a second current mirror circuit, and
the first current mirror circuit and the second current mirror circuit being cascade-connected.
2. The pixel circuit according to claim 1 ,
the second current mirror circuit functioning as maintaining means for maintaining a ratio between the data current and the driving current substantially constant, irrespective of a voltage of the electro-optical element.
3. The pixel circuit according to claim 2 , further comprising:
means for causing the gate of the driving transistor to be in a floating state; and
means for causing the gate of the current supply transistor to be in the floating state.
4. An electro-optical device comprising a plurality of pixel circuits as set forth in claim 1 arranged in a planar fashion.
5. An electronic apparatus comprising the electro-optical device as set forth in claim 4 as a display device.