A display device which operates appropriately independently of the manufacture variations of each element formed over a substrate is provided without increasing the number of components. The display device includes an external correction circuit and a panel, and the external correction circuit and the panel are connected to each other through a flexible printed wiring connecting portion. The panel includes a signal line driver circuit, a scan line driver circuit, a pixel portion, a monitoring element portion, a D/A converter and a constant current source. When mounting the D/A converter on a substrate, the number of external circuit components can be reduced without increasing flexible printed wiring terminals by supplying a digital signal inputted to the D/A converter from a video signal line, and controlling the sampling timing of the digital signal with a signal used in the panel.
1. A display device comprising:
an external correction circuit including a power source and a signal generator; and
a panel being connected to the external correction circuit through a flexible printed wiring, the panel including:
a signal line driver circuit, a scan line driver circuit, a pixel portion including a first thin film transistor, a second thin film transistor and a light-emitting element, a monitoring element portion including a monitoring element and a monitoring line, a D/A converter, and a constant current source circuit, which are formed over a substrate,
wherein the signal generator is configured to send a video signal to the signal line driver circuit and the D/A converter through a video signal line,
wherein the D/A converter is configured to convert the video signal into an analog signal and to send the analog signal to the constant current source circuit,
wherein the constant current source circuit is configured to supply a constant current to the monitoring element through the monitoring line, and a current value of the constant current is controlled based on a potential of the analog signal,
wherein a potential of the monitoring line, which corresponds to a potential difference of the monitoring element, is inputted into the external correction circuit,
wherein the signal line driver circuit is configured to send the video signal to one of a source and a drain of the first thin film transistor,
wherein the other of the source and the drain of the first thin film transistor is electrically connected to a gate of the second thin film transistor, and a gate of the first thin film transistor is electrically connected to the scan line driver circuit,
wherein one of a source and a drain of the second thin film transistor is electrically connected to the light-emitting element, and
wherein the external correction circuit is configured to send the potential of the monitoring line to the other of the source and the drain of the second thin film transistor.
2. The display device according to claim 1 , wherein the potential of the monitoring line is inputted to the light-emitting element through the second thin film transistor.
3. The display device according to claim 1 , wherein the video signal is sampled by the D/A converter during a fly-back period.
4. The display device according to claim 1 , wherein a timing for sampling the video signal by the D/A converter is controlled with a signal used in the panel.